API Documentation

Overview

The AsyncSSH API is modeled after the new Python asyncio framework, with a create_connection() coroutine to create an SSH client and a create_server() coroutine to create an SSH server. Like the asyncio framework, these calls take a parameter of a factory which creates protocol objects to manage the connections once they are open. For AsyncSSH, create_connection() should be passed a client_factory which returns objects derived from SSHClient and create_server() should be passed a server_factory which returns objects derived from SSHServer. In addition, each connection will have an associated SSHClientConnection or SSHServerConnection object passed to the protocol objects which can be used to perform actions on the connection.

For client connections, authentication can be performed by passing in a username and password or SSH keys as arguments to create_connection() or by implementing handler methods on the SSHClient object which return credentials when the server requests them. If no credentials are provided, AsyncSSH automatically attempts to send the username of the local user and the keys found in their .ssh subdirectory. A list of expected server host keys can also be specified, with AsyncSSH defaulting to looking for matching lines in the user’s .ssh/known_hosts file.

For server connections, handlers can be implemented on the SSHServer object to return which authentication methods are supported and to validate credentials provided by clients.

Once an SSH client connection is established and authentication is successful, multiple simultaneous channels can be opened on it. This is accomplished calling methods such as create_session(), create_connection(), and create_unix_connection() on the SSHClientConnection object. The client can also set up listeners on remote TCP ports and UNIX domain sockets by calling create_server() and create_unix_server(). All of these methods take session_factory arguments that return SSHClientSession, SSHTCPSession, or SSHUNIXSession objects used to manage the channels once they are open. Alternately, channels can be opened using open_session(), open_connection(), or open_unix_connection(), which return SSHReader and SSHWriter objects that can be used to perform I/O on the channel. The methods start_server() and start_unix_server() can be used to set up listeners on remote TCP ports or UNIX domain sockets and get back these SSHReader and SSHWriter objects in a callback when new connections are opened.

SSH client sessions can also be opened by calling create_process(). This returns a SSHClientProcess object which has members stdin, stdout, and stderr which are SSHReader and SSHWriter objects. This API also makes it very easy to redirect input and output from the remote process to local files, pipes, sockets, or other SSHReader and SSHWriter objects. In cases where you just want to run a remote process to completion and get back an object containing captured output and exit status, the run() method can be used. It returns an SSHCompletedProcess with the results of the run, or can be set up to raise ProcessError if the process exits with a non-zero exit status.

The client can also set up TCP port forwarding by calling forward_local_port() or forward_remote_port() and UNIX domain socket forwarding by calling forward_local_path() or forward_remote_path(). In these cases, data transfer on the channels is managed automatically by AsyncSSH whenever new connections are opened, so custom session objects are not required.

When an SSH server receives a new connection and authentication is successful, handlers such as session_requested(), connection_requested(), unix_connection_requested(), server_requested(), and unix_server_requested() on the associated SSHServer object will be called when clients attempt to open channels or set up listeners. These methods return coroutines which can set up the requested sessions or connections, returning SSHServerSession or SSHTCPSession objects or handler functions that accept SSHReader and SSHWriter objects as arguments which manage the channels once they are open.

To better support interactive server applications, AsyncSSH defaults to providing echoing of input and basic line editing capabilities when an inbound SSH session requests a pseudo-terminal. This behavior can be disabled by setting the line_editor argument to False when starting up an SSH server. When this feature is enabled, server sessions can enable or disable line mode using the set_line_mode() method of SSHLineEditorChannel. They can also enable or disable input echoing using the set_echo() method.

Each session object also has an associated SSHClientChannel, SSHServerChannel, or SSHTCPChannel object passed to it which can be used to perform actions on the channel. These channel objects provide a superset of the functionality found in asyncio transport objects.

In addition to the above functions and classes, helper functions for importing public and private keys can be found below under Public Key Support, exceptions can be found under Exceptions, supported algorithms can be found under Supported Algorithms, and some useful constants can be found under Constants.

Main Functions

create_connection

asyncssh.create_connection(client_factory, host, port=22, *, loop=None, tunnel=None, family=0, flags=0, local_addr=None, known_hosts=(), username=None, password=None, client_keys=(), passphrase=None, agent_path=(), agent_forwarding=False, client_version=(), kex_algs=(), encryption_algs=(), mac_algs=(), compression_algs=(), signature_algs=(), rekey_bytes=1073741824, rekey_seconds=3600)

Create an SSH client connection

This function is a coroutine which can be run to create an outbound SSH client connection to the specified host and port.

When successful, the following steps occur:

1. The connection is established and an SSHClientConnection object is created to represent it.
2. The client_factory is called without arguments and should return an SSHClient object.
3. The client object is tied to the connection and its connection_made() method is called.
4. The SSH handshake and authentication process is initiated, calling methods on the client object if needed.
5. When authentication completes successfully, the client’s auth_completed() method is called.
6. The coroutine returns the (connection, client) pair. At this point, the connection is ready for sessions to be opened or port forwarding to be set up.

If an error occurs, it will be raised as an exception and the partially open connection and client objects will be cleaned up.

Note

Unlike socket.create_connection(), asyncio calls to create a connection do not support a timeout parameter. However, asyncio calls can be wrapped in a call to asyncio.wait_for() or asyncio.wait() which takes a timeout and provides equivalent functionality.

Parameters:

• client_factory (callable) – A callable which returns an SSHClient object that will be tied to the connection
• host (str) – The hostname or address to connect to
• port (int) – (optional) The port number to connect to. If not specified, the default SSH port is used.
• loop – (optional) The event loop to use when creating the connection. If not specified, the default event loop is used.
• tunnel (SSHClientConnection) – (optional) An existing SSH client connection that this new connection should be tunneled over. If set, a direct TCP/IP tunnel will be opened over this connection to the requested host and port rather than connecting directly via TCP.
• family (socket.AF_UNSPEC, socket.AF_INET, or socket.AF_INET6) – (optional) The address family to use when creating the socket. By default, the address family is automatically selected based on the host.
• flags (flags to pass to getaddrinfo()) – (optional) The flags to pass to getaddrinfo() when looking up the host address
• local_addr (tuple of str and int) – (optional) The host and port to bind the socket to before connecting
• known_hosts (see Specifying known hosts) – (optional) The list of keys which will be used to validate the server host key presented during the SSH handshake. If this is not specified, the keys will be looked up in the file .ssh/known_hosts. If this is explicitly set to None, server host key validation will be disabled.
• username (str) – (optional) Username to authenticate as on the server. If not specified, the currently logged in user on the local machine will be used.
• password (str) – (optional) The password to use for client password authentication or keyboard-interactive authentication which prompts for a password. If this is not specified, client password authentication will not be performed.
• client_keys (see Specifying private keys) – (optional) A list of keys which will be used to authenticate this client via public key authentication. If no client keys are specified, an attempt will be made to get them from an ssh-agent process. If that is not available, an attempt will be made to load them from the files .ssh/id_ed25519, .ssh/id_ecdsa, .ssh/id_rsa, and .ssh/id_dsa in the user’s home directory, with optional certificates loaded from the files .ssh/id_ed25519-cert.pub, .ssh/id_ecdsa-cert.pub, .ssh/id_rsa-cert.pub, and .ssh/id_dsa-cert.pub. If this argument is explicitly set to None, client public key authentication will not be performed.
• passphrase (str) – (optional) The passphrase to use to decrypt client keys when loading them, if they are encrypted. If this is not specified, only unencrypted client keys can be loaded. If the keys passed into client_keys are already loaded, this argument is ignored.
• agent_path (str or SSHServerConnection) – (optional) The path of a UNIX domain socket to use to contact an ssh-agent process which will perform the operations needed for client public key authentication, or the SSHServerConnection to use to forward ssh-agent requests over. If this is not specified and the environment variable SSH_AUTH_SOCK is set, its value will be used as the path. If client_keys is specified or this argument is explicitly set to None, an ssh-agent will not be used.
• agent_forwarding (bool) – (optional) Whether or not to allow forwarding of ssh-agent requests from processes running on the server. By default, ssh-agent forwarding requests from the server are not allowed.
• client_version (str) – (optional) An ASCII string to advertise to the SSH server as the version of this client, defaulting to AsyncSSH and its version number.
• kex_algs (list of str) – (optional) A list of allowed key exchange algorithms in the SSH handshake, taken from key exchange algorithms
• encryption_algs (list of str) – (optional) A list of encryption algorithms to use during the SSH handshake, taken from encryption algorithms
• mac_algs (list of str) – (optional) A list of MAC algorithms to use during the SSH handshake, taken from MAC algorithms
• compression_algs (list of str) – (optional) A list of compression algorithms to use during the SSH handshake, taken from compression algorithms, or None to disable compression
• signature_algs (list of str) – (optional) A list of public key signature algorithms to use during the SSH handshake, taken from signature algorithms
• rekey_bytes (int) – (optional) The number of bytes which can be sent before the SSH session key is renegotiated. This defaults to 1 GB.
• rekey_seconds (int) – (optional) The maximum time in seconds before the SSH session key is renegotiated. This defaults to 1 hour.

Returns:

An SSHClientConnection and SSHClient

create_server

asyncssh.create_server(server_factory, host=None, port=22, *, loop=None, family=0, flags=1, backlog=100, reuse_address=None, server_host_keys, passphrase=None, authorized_client_keys=None, server_version=(), kex_algs=(), encryption_algs=(), mac_algs=(), compression_algs=(), signature_algs=(), allow_pty=True, line_editor=True, line_history=1000, x11_forwarding=False, x11_auth_path=None, agent_forwarding=True, session_factory=None, session_encoding='utf-8', sftp_factory=None, window=2097152, max_pktsize=32768, rekey_bytes=1073741824, rekey_seconds=3600, login_timeout=120)

Create an SSH server

This function is a coroutine which can be run to create an SSH server bound to the specified host and port. The return value is an object derived from asyncio.AbstractServer which can be used to later shut down the server.

Parameters:

• server_factory (callable) – A callable which returns an SSHServer object that will be created for each new inbound connection
• host (str) – (optional) The hostname or address to listen on. If not specified, listeners are created for all addresses.
• port (int) – (optional) The port number to listen on. If not specified, the default SSH port is used.
• loop – (optional) The event loop to use when creating the server. If not specified, the default event loop is used.
• family (socket.AF_UNSPEC, socket.AF_INET, or socket.AF_INET6) – (optional) The address family to use when creating the server. By default, the address families are automatically selected based on the host.
• flags (flags to pass to getaddrinfo()) – (optional) The flags to pass to getaddrinfo() when looking up the host
• backlog (int) – (optional) The maximum number of queued connections allowed on listeners
• reuse_address (bool) – (optional) Whether or not to reuse a local socket in the TIME_WAIT state without waiting for its natural timeout to expire. If not specified, this will be automatically set to True on UNIX.
• server_host_keys (see Specifying private keys) – A list of private keys and optional certificates which can be used by the server as a host key. This argument must be specified.
• passphrase (str) – (optional) The passphrase to use to decrypt server host keys when loading them, if they are encrypted. If this is not specified, only unencrypted server host keys can be loaded. If the keys passed into server_host_keys are already loaded, this argument is ignored.
• authorized_client_keys (see Specifying authorized keys) – (optional) A list of authorized user and CA public keys which should be trusted for certifcate-based client public key authentication.
• server_version (str) – (optional) An ASCII string to advertise to SSH clients as the version of this server, defaulting to AsyncSSH and its version number.
• kex_algs (list of str) – (optional) A list of allowed key exchange algorithms in the SSH handshake, taken from key exchange algorithms
• encryption_algs (list of str) – (optional) A list of encryption algorithms to use during the SSH handshake, taken from encryption algorithms
• mac_algs (list of str) – (optional) A list of MAC algorithms to use during the SSH handshake, taken from MAC algorithms
• compression_algs (list of str) – (optional) A list of compression algorithms to use during the SSH handshake, taken from compression algorithms, or None to disable compression
• signature_algs (list of str) – (optional) A list of public key signature algorithms to use during the SSH handshake, taken from signature algorithms
• allow_pty (bool) – (optional) Whether or not to allow allocation of a pseudo-tty in sessions, defaulting to True
• line_editor (bool) – (optional) Whether or not to enable input line editing on sessions which have a pseudo-tty allocated, defaulting to True
• line_history (bool) – (int) The number of lines of input line history to store in the line editor when it is enabled, defaulting to 1000
• x11_forwarding (bool) – (optional) Whether or not to allow forwarding of X11 connections back to the client when the client supports it, defaulting to False
• x11_auth_path (str) – (optional) The path to the Xauthority file to write X11 authentication data to, defaulting to the value in the environment variable XAUTHORITY or the file .Xauthority in the user’s home directory if that’s not set
• agent_forwarding (bool) – (optional) Whether or not to allow forwarding of ssh-agent requests back to the client when the client supports it, defaulting to True
• session_factory (callable) – (optional) A callable or coroutine handler function which takes AsyncSSH stream objects for stdin, stdout, and stderr that will be called each time a new shell, exec, or subsystem other than SFTP is requested by the client. If not specified, sessions are rejected by default unless the session_requested() method is overridden on the SSHServer object returned by server_factory to make this decision.
• session_encoding (str) – (optional) The Unicode encoding to use for data exchanged on sessions on this server, defaulting to UTF-8 (ISO 10646) format. If None is passed in, the application can send and receive raw bytes.
• sftp_factory (callable) – (optional) A callable which returns an SFTPServer object that will be created each time an SFTP session is requested by the client, or True to use the base SFTPServer class to handle SFTP requests. If not specified, SFTP sessions are rejected by default.
• window (int) – (optional) The receive window size for sessions on this server
• max_pktsize (int) – (optional) The maximum packet size for sessions on this server
• rekey_bytes (int) – (optional) The number of bytes which can be sent before the SSH session key is renegotiated, defaulting to 1 GB
• rekey_seconds (int) – (optional) The maximum time in seconds before the SSH session key is renegotiated, defaulting to 1 hour
• login_timeout (int) – (optional) The maximum time in seconds allowed for authentication to complete, defaulting to 2 minutes

Returns:

asyncio.AbstractServer

connect

asyncssh.connect(host, port=22, **kwargs)

Make an SSH client connection

This function is a coroutine wrapper around create_connection() which can be used when a custom SSHClient instance is not needed. It takes all the same arguments as create_connection() except for client_factory and returns only the SSHClientConnection object rather than a tuple of an SSHClientConnection and SSHClient.

When using this call, the following restrictions apply:

1. No callbacks are called when the connection is successfully opened, when it is closed, or when authentication completes.
2. Any authentication information must be provided as arguments to this call, as any authentication callbacks will deny other authentication attempts. Also, authentication banner information will be ignored.
3. Any debug messages sent by the server will be ignored.

listen

asyncssh.listen(host=None, port=22, *, server_host_keys, **kwargs)

Start an SSH server

This function is a coroutine wrapper around create_server() which can be used when a custom SSHServer instance is not needed. It takes all the same arguments as create_server() except for server_factory.

When using this call, the following restrictions apply:

1. No callbacks are called when a new connection arrives, when a connection is closed, or when authentication completes.
2. Any authentication information must be provided as arguments to this call, as any authentication callbacks will deny other authentication attempts. Currently, this allows only public key authentication to be used, by passing in the authorized_client_keys argument.
3. Only handlers using the streams API are supported and the same handlers must be used for all clients. These handlers must be provided in the session_factory and/or sftp_factory arguments to this call.
4. Any debug messages sent by the client will be ignored.

Main Classes

SSHClient

class asyncssh.SSHClient

SSH client protocol handler

Applications should subclass this when implementing an SSH client. The functions listed below should be overridden to define application-specific behavior. In particular, the method auth_completed() should be defined to open the desired SSH channels on this connection once authentication has been completed.

For simple password or public key based authentication, nothing needs to be defined here if the password or client keys are passed in when the connection is created. However, to prompt interactively or otherwise dynamically select these values, the methods password_auth_requested() and/or public_key_auth_requested() can be defined. Keyboard-interactive authentication is also supported via kbdint_auth_requested() and kbdint_challenge_received().

If the server sends an authentication banner, the method auth_banner_received() will be called.

If the server requires a password change, the method password_change_requested() will be called, followed by either password_changed() or password_change_failed() depending on whether the password change is successful.

General connection handlers
connection_made(connection) Called when a connection is made This method is called as soon as the TCP connection completes. The connection parameter should be stored if needed for later use. Parameters:connection (SSHClientConnection) – The connection which was successfully opened
connection_lost(exc) Called when a connection is lost or closed This method is called when a connection is closed. If the connection is shut down cleanly, exc will be None. Otherwise, it will be an exception explaining the reason for the disconnect. Parameters:exc (Exception) – The exception which caused the connection to close, or None if the connection closed cleanly
debug_msg_received(msg, lang, always_display) A debug message was received on this connection This method is called when the other end of the connection sends a debug message. Applications should implement this method if they wish to process these debug messages. Parameters: msg (str) – The debug message sent lang (str) – The language the message is in always_display (bool) – Whether or not to display the message

General authentication handlers
auth_banner_received(msg, lang) An incoming authentication banner was received This method is called when the server sends a banner to display during authentication. Applications should implement this method if they wish to do something with the banner. Parameters: msg (str) – The message the server wanted to display lang (str) – The language the message is in
auth_completed() Authentication was completed successfully This method is called when authentication has completed succesfully. Applications may use this method to create whatever client sessions and direct TCP/IP or UNIX domain connections are needed and/or set up listeners for incoming TCP/IP or UNIX domain connections coming from the server.

Public key authentication handlers

public_key_auth_requested() Public key authentication has been requested This method should return a private key corresponding to the user that authentication is being attempted for. This method may be called multiple times and can return a different key to try each time it is called. When there are no keys left to try, it should return None to indicate that some other authentication method should be tried. If client keys were provided when the connection was opened, they will be tried before this method is called. If blocking operations need to be performed to determine the key to authenticate with, this method may be defined as a coroutine. Returns:A key as described in Specifying private keys or None to move on to another authentication method

Password authentication handlers
password_auth_requested() Password authentication has been requested This method should return a string containing the password corresponding to the user that authentication is being attempted for. It may be called multiple times and can return a different password to try each time, but most servers have a limit on the number of attempts allowed. When there’s no password left to try, this method should return None to indicate that some other authentication method should be tried. If a password was provided when the connection was opened, it will be tried before this method is called. If blocking operations need to be performed to determine the password to authenticate with, this method may be defined as a coroutine. Returns:A string containing the password to authenticate with or None to move on to another authentication method
password_change_requested(prompt, lang) A password change has been requested This method is called when password authentication was attempted and the user’s password was expired on the server. To request a password change, this method should return a tuple or two strings containing the old and new passwords. Otherwise, it should return NotImplemented. If blocking operations need to be performed to determine the passwords to authenticate with, this method may be defined as a coroutine. By default, this method returns NotImplemented. Parameters: prompt (str) – The prompt requesting that the user enter a new password lang (str) – The language that the prompt is in Returns: A tuple of two strings containing the old and new passwords or NotImplemented if password changes aren’t supported
password_changed() The requested password change was successful This method is called to indicate that a requested password change was successful. It is generally followed by a call to auth_completed() since this means authentication was also successful.
password_change_failed() The requested password change has failed This method is called to indicate that a requested password change failed, generally because the requested new password doesn’t meet the password criteria on the remote system. After this method is called, other forms of authentication will automatically be attempted.

Keyboard-interactive authentication handlers
kbdint_auth_requested() Keyboard-interactive authentication has been requested This method should return a string containing a comma-separated list of submethods that the server should use for keyboard-interactive authentication. An empty string can be returned to let the server pick the type of keyboard-interactive authentication to perform. If keyboard-interactive authentication is not supported, None should be returned. By default, keyboard-interactive authentication is supported if a password was provided when the SSHClient was created and it hasn’t been sent yet. If the challenge is not a password challenge, this authentication will fail. This method and the kbdint_challenge_received() method can be overridden if other forms of challenge should be supported. If blocking operations need to be performed to determine the submethods to request, this method may be defined as a coroutine. Returns:A string containing the submethods the server should use for authentication or None to move on to another authentication method
kbdint_challenge_received(name, instruction, lang, prompts) A keyboard-interactive auth challenge has been received This method is called when the server sends a keyboard-interactive authentication challenge. The return value should be a list of strings of the same length as the number of prompts provided if the challenge can be answered, or None to indicate that some other form of authentication should be attempted. If blocking operations need to be performed to determine the responses to authenticate with, this method may be defined as a coroutine. By default, this method will look for a challenge consisting of a single ‘Password:’ prompt, and call the method password_auth_requested() to provide the response. It will also ignore challenges with no prompts (generally used to provide instructions). Any other form of challenge will cause this method to return None to move on to another authentication method. Parameters: name (str) – The name of the challenge instruction (str) – Instructions to the user about how to respond to the challenge lang (str) – The language the challenge is in prompts (list of tuples of str and bool) – The challenges the user should respond to and whether or not the responses should be echoed when they are entered Returns: List of string responses to the challenge or None to move on to another authentication method

SSHServer

class asyncssh.SSHServer

SSH server protocol handler

Applications should subclass this when implementing an SSH server. At a minimum, one or more of the authentication handlers will need to be overridden to perform authentication, or begin_auth() should be overridden to return False to indicate that no authentication is required.

In addition, one or more of the session_requested(), connection_requested(), server_requested(), unix_connection_requested(), or unix_server_requested() methods will need to be overridden to handle requests to open sessions or direct connections or set up listeners for forwarded connections.

General connection handlers
connection_made(connection) Called when a connection is made This method is called when a new TCP connection is accepted. The connection parameter should be stored if needed for later use.
connection_lost(exc) Called when a connection is lost or closed This method is called when a connection is closed. If the connection is shut down cleanly, exc will be None. Otherwise, it will be an exception explaining the reason for the disconnect.
debug_msg_received(msg, lang, always_display) A debug message was received on this connection This method is called when the other end of the connection sends a debug message. Applications should implement this method if they wish to process these debug messages. Parameters: msg (str) – The debug message sent lang (str) – The language the message is in always_display (bool) – Whether or not to display the message

General authentication handlers

begin_auth(username) Authentication has been requested by the client This method will be called when authentication is attempted for the specified user. Applications should use this method to prepare whatever state they need to complete the authentication, such as loading in the set of authorized keys for that user. If no authentication is required for this user, this method should return False to cause the authentication to immediately succeed. Otherwise, it should return True to indicate that authentication should proceed. Parameters:username (str) – The name of the user being authenticated Returns:A bool indicating whether authentication is required

Public key authentication handlers
public_key_auth_supported() Return whether or not public key authentication is supported This method should return True if client public key authentication is supported. Applications wishing to support it must have this method return True and implement validate_public_key() to return whether or not the key provided by the client is valid for the user being authenticated. By default, it returns False indicating the client public key authentication is not supported. Returns:A bool indicating if public key authentication is supported or not
validate_public_key(username, key) Return whether key is an authorized client key for this user Basic key-based client authentication can be supported by passing authorized keys in the authorized_client_keys argument of create_server(), or by calling set_authorized_keys on the server connection from the begin_auth() method. However, for more flexibility in matching on the allowed set of keys, this method can be implemented by the application to do the matching itself. It should return True if the specified key is a valid client key for the user being authenticated. This method may be called multiple times with different keys provided by the client. Applications should precompute as much as possible in the begin_auth() method so that this function can quickly return whether the key provided is in the list. If blocking operations need to be performed to determine the validity of the key, this method may be defined as a coroutine. By default, this method returns False for all client keys. Note This function only needs to report whether the public key provided is a valid client key for this user. If it is, AsyncSSH will verify that the client possesses the corresponding private key before allowing the authentication to succeed. Parameters: username (str) – The user being authenticated key (SSHKey public key) – The public key sent by the client Returns: A bool indicating if the specified key is a valid client key for the user being authenticated
validate_ca_key(username, key) Return whether key is an authorized CA key for this user Basic key-based client authentication can be supported by passing authorized keys in the authorized_client_keys argument of create_server(), or by calling set_authorized_keys on the server connection from the begin_auth() method. However, for more flexibility in matching on the allowed set of keys, this method can be implemented by the application to do the matching itself. It should return True if the specified key is a valid certificate authority key for the user being authenticated. This method may be called multiple times with different keys provided by the client. Applications should precompute as much as possible in the begin_auth() method so that this function can quickly return whether the key provided is in the list. If blocking operations need to be performed to determine the validity of the key, this method may be defined as a coroutine. By default, this method returns False for all CA keys. Note This function only needs to report whether the public key provided is a valid CA key for this user. If it is, AsyncSSH will verify that the certificate is valid, that the user is one of the valid principals for the certificate, and that the client possesses the private key corresponding to the public key in the certificate before allowing the authentication to succeed. Parameters: username (str) – The user being authenticated key (SSHKey public key) – The public key which signed the certificate sent by the client Returns: A bool indicating if the specified key is a valid CA key for the user being authenticated

Password authentication handlers
password_auth_supported() Return whether or not password authentication is supported This method should return True if password authentication is supported. Applications wishing to support it must have this method return True and implement validate_password() to return whether or not the password provided by the client is valid for the user being authenticated. By default, this method returns False indicating that password authentication is not supported. Returns:A bool indicating if password authentication is supported or not
validate_password(username, password) Return whether password is valid for this user This method should return True if the specified password is a valid password for the user being authenticated. It must be overridden by applications wishing to support password authentication. If the password provided is valid but expired, this method may raise PasswordChangeRequired to request that the client provide a new password before authentication is allowed to complete. In this case, the application must override change_password() to handle the password change request. This method may be called multiple times with different passwords provided by the client. Applications may wish to limit the number of attempts which are allowed. This can be done by having password_auth_supported() begin returning False after the maximum number of attempts is exceeded. If blocking operations need to be performed to determine the validity of the password, this method may be defined as a coroutine. By default, this method returns False for all passwords. Parameters: username (str) – The user being authenticated password (str) – The password sent by the client Returns: A bool indicating if the specified password is valid for the user being authenticated Raises: PasswordChangeRequired if the password provided is expired and needs to be changed
change_password(username, old_password, new_password) Handle a request to change a user’s password This method is called when a user makes a request to change their password. It should first validate that the old password provided is correct and then attempt to change the user’s password to the new value. If the old password provided is valid and the change to the new password is successful, this method should return True. If the old password is not valid or password changes are not supported, it should return False. It may also raise PasswordChangeRequired to request that the client try again if the new password is not acceptable for some reason. If blocking operations need to be performed to determine the validity of the old password or to change to the new password, this method may be defined as a coroutine. By default, this method returns False, rejecting all password changes. Parameters: username (str) – The user whose password should be changed old_password (str) – The user’s current password new_password (str) – The new password being requested Returns: A bool indicating if the password change is successful or not Raises: PasswordChangeRequired if the new password is not acceptable and the client should be asked to provide another

Keyboard-interactive authentication handlers
kbdint_auth_supported() Return whether or not keyboard-interactive authentication is supported This method should return True if keyboard-interactive authentication is supported. Applications wishing to support it must have this method return True and implement get_kbdint_challenge() and validate_kbdint_response() to generate the apporiate challenges and validate the responses for the user being authenticated. By default, this method returns NotImplemented tying this authentication to password authentication. If the application implements password authentication and this method is not overridden, keyboard-interactive authentication will be supported by prompting for a password and passing that to the password authentication callbacks. Returns:A bool indicating if keyboard-interactive authentication is supported or not
get_kbdint_challenge(username, lang, submethods) Return a keyboard-interactive auth challenge This method should return True if authentication should succeed without any challenge, False if authentication should fail without any challenge, or an auth challenge consisting of a challenge name, instructions, a language tag, and a list of tuples containing prompt strings and booleans indicating whether input should be echoed when a value is entered for that prompt. If blocking operations need to be performed to determine the challenge to issue, this method may be defined as a coroutine. Parameters: username (str) – The user being authenticated lang (str) – The language requested by the client for the challenge submethods (str) – A comma-separated list of the types of challenges the client can support, or the empty string if the server should choose Returns: An authentication challenge as described above
validate_kbdint_response(username, responses) Return whether the keyboard-interactive response is valid for this user This method should validate the keyboard-interactive responses provided and return True if authentication should succeed with no further challenge, False if authentication should fail, or an additional auth challenge in the same format returned by get_kbdint_challenge(). Any series of challenges can be returned this way. To print a message in the middle of a sequence of challenges without prompting for additional data, a challenge can be returned with an empty list of prompts. After the client acknowledges this message, this function will be called again with an empty list of responses to continue the authentication. If blocking operations need to be performed to determine the validity of the response or the next challenge to issue, this method may be defined as a coroutine. Parameters: username (str) – The user being authenticated responses (list of str) – A list of responses to the last challenge Returns: True, False, or the next challenge

Channel session open handlers
session_requested() Handle an incoming session request This method is called when a session open request is received from the client, indicating it wishes to open a channel to be used for running a shell, executing a command, or connecting to a subsystem. If the application wishes to accept the session, it must override this method to return either an SSHServerSession object to use to process the data received on the channel or a tuple consisting of an SSHServerChannel object created with create_server_channel and an SSHServerSession, if the application wishes to pass non-default arguments when creating the channel. If blocking operations need to be performed before the session can be created, a coroutine which returns an SSHServerSession object can be returned instead of the session iself. This can be either returned directly or as a part of a tuple with an SSHServerChannel object. To reject this request, this method should return False to send back a “Session refused” response or raise a ChannelOpenError exception with the reason for the failure. The details of what type of session the client wants to start will be delivered to methods on the SSHServerSession object which is returned, along with other information such as environment variables, terminal type, size, and modes. By default, all session requests are rejected. Returns:One of the following: An SSHServerSession object or a coroutine which returns an SSHServerSession A tuple consisting of an SSHServerChannel and the above A callable or coroutine handler function which takes AsyncSSH stream objects for stdin, stdout, and stderr as arguments A tuple consisting of an SSHServerChannel and the above False to refuse the request Raises:ChannelOpenError if the session shouldn’t be accepted
connection_requested(dest_host, dest_port, orig_host, orig_port) Handle a direct TCP/IP connection request This method is called when a direct TCP/IP connection request is received by the server. Applications wishing to accept such connections must override this method. To allow standard port forwarding of data on the connection to the requested destination host and port, this method should return True. To reject this request, this method should return False to send back a “Connection refused” response or raise an ChannelOpenError exception with the reason for the failure. If the application wishes to process the data on the connection itself, this method should return either an SSHTCPSession object which can be used to process the data received on the channel or a tuple consisting of of an SSHTCPChannel object created with create_tcp_channel() and an SSHTCPSession, if the application wishes to pass non-default arguments when creating the channel. If blocking operations need to be performed before the session can be created, a coroutine which returns an SSHTCPSession object can be returned instead of the session iself. This can be either returned directly or as a part of a tuple with an SSHTCPChannel object. By default, all connection requests are rejected. Parameters: dest_host (str) – The address the client wishes to connect to dest_port (int) – The port the client wishes to connect to orig_host (str) – The address the connection was originated from orig_port (int) – The port the connection was originated from Returns: One of the following: An SSHTCPSession object or a coroutine which returns an SSHTCPSession A tuple consisting of an SSHTCPChannel and the above A callable or coroutine handler function which takes AsyncSSH stream objects for reading from and writing to the connection A tuple consisting of an SSHTCPChannel and the above True to request standard port forwarding False to refuse the connection Raises: ChannelOpenError if the connection shouldn’t be accepted
unix_connection_requested(dest_path) Handle a direct UNIX domain socket connection request This method is called when a direct UNIX domain socket connection request is received by the server. Applications wishing to accept such connections must override this method. To allow standard path forwarding of data on the connection to the requested destination path, this method should return True. To reject this request, this method should return False to send back a “Connection refused” response or raise an ChannelOpenError exception with the reason for the failure. If the application wishes to process the data on the connection itself, this method should return either an SSHUNIXSession object which can be used to process the data received on the channel or a tuple consisting of of an SSHUNIXChannel object created with create_unix_channel() and an SSHUNIXSession, if the application wishes to pass non-default arguments when creating the channel. If blocking operations need to be performed before the session can be created, a coroutine which returns an SSHUNIXSession object can be returned instead of the session iself. This can be either returned directly or as a part of a tuple with an SSHUNIXChannel object. By default, all connection requests are rejected. Parameters:dest_path (str) – The path the client wishes to connect to Returns:One of the following: An SSHUNIXSession object or a coroutine which returns an SSHUNIXSession A tuple consisting of an SSHUNIXChannel and the above A callable or coroutine handler function which takes AsyncSSH stream objects for reading from and writing to the connection A tuple consisting of an SSHUNIXChannel and the above True to request standard path forwarding False to refuse the connection Raises:ChannelOpenError if the connection shouldn’t be accepted
server_requested(listen_host, listen_port) Handle a request to listen on a TCP/IP address and port This method is called when a client makes a request to listen on an address and port for incoming TCP connections. The port to listen on may be 0 to request a dynamically allocated port. Applications wishing to allow TCP/IP connection forwarding must override this method. To set up standard port forwarding of connections received on this address and port, this method should return True. If the application wishes to manage listening for incoming connections itself, this method should return an SSHListener object that listens for new connections and calls create_connection on each of them to forward them back to the client or return None if the listener can’t be set up. If blocking operations need to be performed to set up the listener, a coroutine which returns an SSHListener can be returned instead of the listener itself. To reject this request, this method should return False. By default, this method rejects all server requests. Parameters: listen_host (str) – The address the server should listen on listen_port (int) – The port the server should listen on, or the value 0 to request that the server dynamically allocate a port Returns: One of the following: An SSHListener object or a coroutine which returns an SSHListener or False if the listener can’t be opened True to set up standard port forwarding False to reject the request
unix_server_requested(listen_path) Handle a request to listen on a UNIX domain socket This method is called when a client makes a request to listen on a path for incoming UNIX domain socket connections. Applications wishing to allow UNIX domain socket forwarding must override this method. To set up standard path forwarding of connections received on this path, this method should return True. If the application wishes to manage listening for incoming connections itself, this method should return an SSHListener object that listens for new connections and calls create_unix_connection on each of them to forward them back to the client or return None if the listener can’t be set up. If blocking operations need to be performed to set up the listener, a coroutine which returns an SSHListener can be returned instead of the listener itself. To reject this request, this method should return False. By default, this method rejects all server requests. Parameters:listen_path (str) – The path the server should listen on Returns:One of the following: An SSHListener object or a coroutine which returns an SSHListener or False if the listener can’t be opened True to set up standard path forwarding False to reject the request

Connection Classes

SSHClientConnection

class asyncssh.SSHClientConnection

SSH client connection

This class represents an SSH client connection.

Once authentication is successful on a connection, new client sessions can be opened by calling create_session().

Direct TCP connections can be opened by calling create_connection().

Remote listeners for forwarded TCP connections can be opened by calling create_server().

Direct UNIX domain socket connections can be opened by calling create_unix_connection().

Remote listeners for forwarded UNIX domain socket connections can be opened by calling create_unix_server().

TCP port forwarding can be set up by calling forward_local_port() or forward_remote_port().

UNIX domain socket forwarding can be set up by calling forward_local_path() or forward_remote_path().

General connection methods
get_extra_info(name, default=None) Get additional information about the connection This method returns extra information about the connection once it is established. Supported values include everything supported by a socket transport plus: username client_version server_version send_cipher send_mac send_compression recv_cipher recv_mac recv_compression See get_extra_info() in asyncio.BaseTransport for more information.
send_debug(msg, lang='en-US', always_display=False) Send a debug message on this connection This method can be called to send a debug message to the other end of the connection. Parameters: msg (str) – The debug message to send lang (str) – The language the message is in always_display (bool) – Whether or not to display the message

Client session open methods
create_session(session_factory, command=None, *, subsystem=None, env={}, term_type=None, term_size=None, term_modes={}, x11_forwarding=False, x11_display=None, x11_auth_path=None, x11_single_connection=False, encoding='utf-8', window=2097152, max_pktsize=32768) Create an SSH client session This method is a coroutine which can be called to create an SSH client session used to execute a command, start a subsystem such as sftp, or if no command or subsystem is specified run an interactive shell. Optional arguments allow terminal and environment information to be provided. By default, this class expects string data in its send and receive functions, which it encodes on the SSH connection in UTF-8 (ISO 10646) format. An optional encoding argument can be passed in to select a different encoding, or None can be passed in if the application wishes to send and receive raw bytes. Other optional arguments include the SSH receive window size and max packet size which default to 2 MB and 32 KB, respectively. Parameters: session_factory (callable) – A callable which returns an SSHClientSession object that will be created to handle activity on this session command (str) – (optional) The remote command to execute. By default, an interactive shell is started if no command or subsystem is provided. subsystem (str) – (optional) The name of a remote subsystem to start up env (dictionary) – (optional) The set of environment variables to set for this session. Keys and values passed in here will be converted to Unicode strings encoded as UTF-8 (ISO 10646) for transmission. Note Many SSH servers restrict which environment variables a client is allowed to set. The server’s configuration may need to be edited before environment variables can be successfully set in the remote environment. term_type (str) – (optional) The terminal type to set for this session. If this is not set, a pseudo-terminal will not be requested for this session. term_size (tuple of 2 or 4 integers) – (optional) The terminal width and height in characters and optionally the width and height in pixels term_modes – (optional) POSIX terminal modes to set for this session, where keys are taken from POSIX terminal modes with values defined in section 8 of RFC 4254#section-8. x11_forwarding (bool) – (optional) Whether or not to request X11 forwarding for this session, defaulting to False x11_display (str) – (optional) The display that X11 connections should be forwarded to, defaulting to the value in the environment variable DISPLAY x11_auth_path (str) – (optional) The path to the Xauthority file to read X11 authentication data from, defaulting to the value in the environment variable XAUTHORITY or the file .Xauthority in the user’s home directory if that’s not set x11_single_connection (bool) – (optional) Whether or not to limit X11 forwarding to a single connection, defaulting to False encoding (str) – (optional) The Unicode encoding to use for data exchanged on the connection window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: an SSHClientChannel and SSHClientSession Raises: ChannelOpenError if the session can’t be opened
open_session(*args, **kwargs) Open an SSH client session This method is a coroutine wrapper around create_session() designed to provide a “high-level” stream interface for creating an SSH client session. Instead of taking a session_factory argument for constructing an object which will handle activity on the session via callbacks, it returns an SSHWriter and two SSHReader objects representing stdin, stdout, and stderr which can be used to perform I/O on the session. With the exception of session_factory, all of the arguments to create_session() are supported and have the same meaning.
create_process(*args, bufsize=io.DEFAULT_BUFFER_SIZE, input=None, stdin=PIPE, stdout=PIPE, stderr=PIPE, **kwargs) Create a process on the remote system This method is a coroutine wrapper around create_session() which can be used to execute a command, start a subsystem, or start an interactive shell, optionally redirecting stdin, stdout, and stderr to and from files or pipes attached to other local and remote processes. By default, stdin, stdout, and stderr can be read and written interactively via stream objects which are members of the SSHClientProcess object this method returns. However, if other file-like objects are provided as arguments here, input or output will automatically be redirected to them. The special value DEVNULL can be used to provide no input or discard all output, and the special value STDOUT can be provided as stderr to send its output to the same stream as stdout. In addition to the arguments below, all arguments to create_session() except for session_factory are supported and have the same meaning. Parameters: bufsize (int) – (optional) Buffer size to use when feeding data from a file to stdin input (str or bytes) – (optional) Input data to feed to standard input of the remote process. If specified, this argument takes precedence over stdin. Data should be a str if encoding is set, or bytes if not. stdin – (optional) A filename, file-like object, file descriptor, socket, or SSHReader to feed to standard input of the remote process, or DEVNULL to provide no input. stdout – (optional) A filename, file-like object, file descriptor, socket, or SSHWriter to feed standard output of the remote process to, or DEVNULL to discard this output. stderr – (optional) A filename, file-like object, file descriptor, socket, or SSHWriter to feed standard error of the remote process to, DEVNULL to discard this output, or STDOUT to feed standard error to the same place as stdout. Returns: SSHClientProcess Raises: ChannelOpenError if the channel can’t be opened
run(*args, check=False, **kwargs) Run a command on the remote system and collect its output This method is a coroutine wrapper around create_process() which can be used to run a process to completion when no interactivity is needed. All of the arguments to create_process() can be passed in to provide input or redirect stdin, stdout, and stderr, but this method waits until the process exits and returns an SSHCompletedProcess object with the exit status or signal information and the output to stdout and stderr (if not redirected). If the check argument is set to True, a non-zero exit status from the remote process will trigger the ProcessError exception to be raised. In addition to the argument below, all arguments to create_process() are supported and have the same meaning. Parameters:check (bool) – (optional) Whether or not to raise ProcessError when a non-zero exit status is returned Returns:SSHCompletedProcess Raises: ChannelOpenError if the session can’t be opened ProcessError if checking non-zero exit status
start_sftp_client(path_encoding='utf-8', path_errors='strict') Start an SFTP client This method is a coroutine which attempts to start a secure file transfer session. If it succeeds, it returns an SFTPClient object which can be used to copy and access files on the remote host. An optional Unicode encoding can be specified for sending and receiving pathnames, defaulting to UTF-8 with strict error checking. If an encoding of None is specified, pathnames will be left as bytes rather than being converted to & from strings. Parameters: path_encoding (str) – The Unicode encoding to apply when sending and receiving remote pathnames path_errors (str) – The error handling strategy to apply on encode/decode errors Returns: SFTPClient Raises: SFTPError if the session can’t be opened
create_ssh_connection(client_factory, host, port=22, *args, **kwargs) Create a tunneled SSH client connection This method is a coroutine which can be called to open an SSH client connection to the requested host and port tunneled inside this already established connection. It takes all the same arguments as create_connection() but requests that the upstream SSH server open the connection rather than connecting directly.
connect_ssh(host, port=22, *args, **kwargs) Make a tunneled SSH client connection This method is a coroutine which can be called to open an SSH client connection to the requested host and port tunneled inside this already established connection. It takes all the same arguments as connect() but requests that the upstream SSH server open the connection rather than connecting directly.

Client connection open methods
create_connection(session_factory, remote_host, remote_port, orig_host='', orig_port=0, *, encoding=None, window=2097152, max_pktsize=32768) Create an SSH TCP direct connection This method is a coroutine which can be called to request that the server open a new outbound TCP connection to the specified destination host and port. If the connection is successfully opened, a new SSH channel will be opened with data being handled by a SSHTCPSession object created by session_factory. Optional arguments include the host and port of the original client opening the connection when performing TCP port forwarding. By default, this class expects data to be sent and received as raw bytes. However, an optional encoding argument can be passed in to select the encoding to use, allowing the application send and receive string data. Other optional arguments include the SSH receive window size and max packet size which default to 2 MB and 32 KB, respectively. Parameters: session_factory (callable) – A callable which returns an SSHClientSession object that will be created to handle activity on this session remote_host (str) – The remote hostname or address to connect to remote_port (int) – The remote port number to connect to orig_host (str) – (optional) The hostname or address of the client requesting the connection orig_port (int) – (optional) The port number of the client requesting the connection encoding (str) – (optional) The Unicode encoding to use for data exchanged on the connection window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: an SSHTCPChannel and SSHTCPSession Raises: ChannelOpenError if the connection can’t be opened
open_connection(*args, **kwargs) Open an SSH TCP direct connection This method is a coroutine wrapper around create_connection() designed to provide a “high-level” stream interface for creating an SSH TCP direct connection. Instead of taking a session_factory argument for constructing an object which will handle activity on the session via callbacks, it returns SSHReader and SSHWriter objects which can be used to perform I/O on the connection. With the exception of session_factory, all of the arguments to create_connection() are supported and have the same meaning here. Returns:an SSHReader and SSHWriter Raises:ChannelOpenError if the connection can’t be opened
create_server(session_factory, listen_host, listen_port, *, encoding=None, window=2097152, max_pktsize=32768) Create a remote SSH TCP listener This method is a coroutine which can be called to request that the server listen on the specified remote address and port for incoming TCP connections. If the request is successful, the return value is an SSHListener object which can be used later to shut down the listener. If the request fails, None is returned. Parameters: session_factory (callable or coroutine) – A callable or coroutine which takes arguments of the original host and port of the client and decides whether to accept the connection or not, either returning an SSHTCPSession object used to handle activity on that connection or raising ChannelOpenError to indicate that the connection should not be accepted listen_host (str) – The hostname or address on the remote host to listen on listen_port (int) – The port number on the remote host to listen on encoding (str) – (optional) The Unicode encoding to use for data exchanged on the connection window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: SSHListener or None if the listener can’t be opened
start_server(handler_factory, *args, **kwargs) Start a remote SSH TCP listener This method is a coroutine wrapper around create_server() designed to provide a “high-level” stream interface for creating remote SSH TCP listeners. Instead of taking a session_factory argument for constructing an object which will handle activity on the session via callbacks, it takes a handler_factory which returns a callable or coroutine that will be passed SSHReader and SSHWriter objects which can be used to perform I/O on each new connection which arrives. Like create_server(), handler_factory can also raise ChannelOpenError if the connection should not be accepted. With the exception of handler_factory replacing session_factory, all of the arguments to create_server() are supported and have the same meaning here. Parameters:handler_factory (callable or coroutine) – A callable or coroutine which takes arguments of the original host and port of the client and decides whether to accept the connection or not, either returning a callback or coroutine used to handle activity on that connection or raising ChannelOpenError to indicate that the connection should not be accepted Returns:SSHListener or None if the listener can’t be opened
create_unix_connection(session_factory, remote_path, *, encoding=None, window=2097152, max_pktsize=32768) Create an SSH UNIX domain socket direct connection This method is a coroutine which can be called to request that the server open a new outbound UNIX domain socket connection to the specified destination path. If the connection is successfully opened, a new SSH channel will be opened with data being handled by a SSHUNIXSession object created by session_factory. By default, this class expects data to be sent and received as raw bytes. However, an optional encoding argument can be passed in to select the encoding to use, allowing the application send and receive string data. Other optional arguments include the SSH receive window size and max packet size which default to 2 MB and 32 KB, respectively. Parameters: session_factory (callable) – A callable which returns an SSHClientSession object that will be created to handle activity on this session remote_path (str) – The remote path to connect to encoding (str) – (optional) The Unicode encoding to use for data exchanged on the connection window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: an SSHUNIXChannel and SSHUNIXSession Raises: ChannelOpenError if the connection can’t be opened
open_unix_connection(*args, **kwargs) Open an SSH UNIX domain socket direct connection This method is a coroutine wrapper around create_unix_connection() designed to provide a “high-level” stream interface for creating an SSH UNIX domain socket direct connection. Instead of taking a session_factory argument for constructing an object which will handle activity on the session via callbacks, it returns SSHReader and SSHWriter objects which can be used to perform I/O on the connection. With the exception of session_factory, all of the arguments to create_unix_connection() are supported and have the same meaning here. Returns:an SSHReader and SSHWriter Raises:ChannelOpenError if the connection can’t be opened
create_unix_server(session_factory, listen_path, *, encoding=None, window=2097152, max_pktsize=32768) Create a remote SSH UNIX domain socket listener This method is a coroutine which can be called to request that the server listen on the specified remote path for incoming UNIX domain socket connections. If the request is successful, the return value is an SSHListener object which can be used later to shut down the listener. If the request fails, None is returned. Parameters: session_factory (callable or coroutine) – A callable or coroutine which takes arguments of the original host and port of the client and decides whether to accept the connection or not, either returning an SSHUNIXSession object used to handle activity on that connection or raising ChannelOpenError to indicate that the connection should not be accepted listen_path (str) – The path on the remote host to listen on encoding (str) – (optional) The Unicode encoding to use for data exchanged on the connection window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: SSHListener or None if the listener can’t be opened
start_unix_server(handler_factory, *args, **kwargs) Start a remote SSH UNIX domain socket listener This method is a coroutine wrapper around create_unix_server() designed to provide a “high-level” stream interface for creating remote SSH UNIX domain socket listeners. Instead of taking a session_factory argument for constructing an object which will handle activity on the session via callbacks, it takes a handler_factory which returns a callable or coroutine that will be passed SSHReader and SSHWriter objects which can be used to perform I/O on each new connection which arrives. Like create_unix_server(), handler_factory can also raise ChannelOpenError if the connection should not be accepted. With the exception of handler_factory replacing session_factory, all of the arguments to create_unix_server() are supported and have the same meaning here. Parameters:handler_factory (callable or coroutine) – A callable or coroutine which takes arguments of the original host and port of the client and decides whether to accept the connection or not, either returning a callback or coroutine used to handle activity on that connection or raising ChannelOpenError to indicate that the connection should not be accepted Returns:SSHListener or None if the listener can’t be opened

Client forwarding methods
forward_connection(dest_host, dest_port) Forward a tunneled TCP connection This method is a coroutine which can be returned by a session_factory to forward connections tunneled over SSH to the specified destination host and port. Parameters: dest_host (str) – The hostname or address to forward the connections to dest_port (int) – The port number to forward the connections to Returns: SSHTCPSession
forward_local_port(listen_host, listen_port, dest_host, dest_port) Set up local port forwarding This method is a coroutine which attempts to set up port forwarding from a local listening port to a remote host and port via the SSH connection. If the request is successful, the return value is an SSHListener object which can be used later to shut down the port forwarding. Parameters: listen_host (str) – The hostname or address on the local host to listen on listen_port (int) – The port number on the local host to listen on dest_host (str) – The hostname or address to forward the connections to dest_port (int) – The port number to forward the connections to Returns: SSHListener Raises: OSError if the listener can’t be opened
forward_local_path(listen_path, dest_path) Set up local UNIX domain socket forwarding This method is a coroutine which attempts to set up UNIX domain socket forwarding from a local listening path to a remote path via the SSH connection. If the request is successful, the return value is an SSHListener object which can be used later to shut down the UNIX domain socket forwarding. Parameters: listen_path (str) – The path on the local host to listen on dest_path (str) – The path on the remote host to forward the connections to Returns: SSHListener Raises: OSError if the listener can’t be opened
forward_remote_port(listen_host, listen_port, dest_host, dest_port) Set up remote port forwarding This method is a coroutine which attempts to set up port forwarding from a remote listening port to a local host and port via the SSH connection. If the request is successful, the return value is an SSHListener object which can be used later to shut down the port forwarding. If the request fails, None is returned. Parameters: listen_host (str) – The hostname or address on the remote host to listen on listen_port (int) – The port number on the remote host to listen on dest_host (str) – The hostname or address to forward connections to dest_port (int) – The port number to forward connections to Returns: SSHListener or None if the listener can’t be opened
forward_remote_path(listen_path, dest_path) Set up remote UNIX domain socket forwarding This method is a coroutine which attempts to set up UNIX domain socket forwarding from a remote listening path to a local path via the SSH connection. If the request is successful, the return value is an SSHListener object which can be used later to shut down the port forwarding. If the request fails, None is returned. Parameters: listen_path (str) – The path on the remote host to listen on dest_path (str) – The path on the local host to forward connections to Returns: SSHListener or None if the listener can’t be opened

Connection close methods
abort() Forcibly close the SSH connection This method closes the SSH connection immediately, without waiting for pending operations to complete and wihtout sending an explicit SSH disconnect message. Buffered data waiting to be sent will be lost and no more data will be received. When the the connection is closed, connection_lost() on the associated SSHClient object will be called with the value None.
close() Cleanly close the SSH connection This method calls disconnect() with the reason set to indicate that the connection was closed explicitly by the application.
disconnect(code, reason, lang='en-US') Disconnect the SSH connection This method sends a disconnect message and closes the SSH connection after buffered data waiting to be written has been sent. No more data will be received. When the connection is fully closed, connection_lost() on the associated SSHClient or SSHServer object will be called with the value None. Parameters: code (int) – The reason for the disconnect, from disconnect reason codes reason (str) – A human readable reason for the disconnect lang (str) – The language the reason is in
wait_closed() Wait for this connection to close This method is a coroutine which can be called to block until this connection has finished closing.

SSHServerConnection

class asyncssh.SSHServerConnection

SSH server connection

This class represents an SSH server connection.

During authentication, send_auth_banner() can be called to send an authentication banner to the client.

Once authenticated, SSHServer objects wishing to create session objects with non-default channel properties can call create_server_channel() from their session_requested() method and return a tuple of the SSHServerChannel object returned from that and either an SSHServerSession object or a coroutine which returns an SSHServerSession.

Similarly, SSHServer objects wishing to create TCP connection objects with non-default channel properties can call create_tcp_channel() from their connection_requested() method and return a tuple of the SSHTCPChannel object returned from that and either an SSHTCPSession object or a coroutine which returns an SSHTCPSession.

SSHServer objects wishing to create UNIX domain socket connection objects with non-default channel properties can call create_unix_channel() from the unix_connection_requested() method and return a tuple of the SSHUNIXChannel object returned from that and either an SSHUNIXSession object or a coroutine which returns an SSHUNIXSession.

General connection methods
get_extra_info(name, default=None) Get additional information about the connection This method returns extra information about the connection once it is established. Supported values include everything supported by a socket transport plus: username client_version server_version send_cipher send_mac send_compression recv_cipher recv_mac recv_compression See get_extra_info() in asyncio.BaseTransport for more information.
send_debug(msg, lang='en-US', always_display=False) Send a debug message on this connection This method can be called to send a debug message to the other end of the connection. Parameters: msg (str) – The debug message to send lang (str) – The language the message is in always_display (bool) – Whether or not to display the message

Server authentication methods
send_auth_banner(msg, lang='en-US') Send an authentication banner to the client This method can be called to send an authentication banner to the client, displaying information while authentication is in progress. It is an error to call this method after the authentication is complete. Parameters: msg (str) – The message to display lang (str) – The language the message is in Raises: OSError if authentication is already completed
set_authorized_keys(authorized_keys) Set the keys trusted for client public key authentication This method can be called to set the trusted user and CA keys for client public key authentication. It should generally be called from the begin_auth method of SSHServer to set the appropriate keys for the user attempting to authenticate. Parameters:authorized_keys (see Specifying authorized keys) – The keys to trust for client public key authentication
get_key_option(option, default=None) Return option from authorized_keys If a client key or certificate was presented during authentication, this method returns the value of the requested option in the corresponding authorized_keys entry if it was set. Otherwise, it returns the default value provided. The following standard options are supported: command (string) environment (dictionary of name/value pairs) from (list of host patterns) permitopen (list of host/port tuples) principals (list of usernames) Non-standard options are also supported and will return the value True if the option is present without a value or return a list of strings containing the values associated with each occurrence of that option name. If the option is not present, the specified default value is returned. Parameters: option (str) – The name of the option to look up. default – The default value to return if the option is not present. Returns: The value of the option in authorized_keys, if set
check_key_permission(permission) Check permissions in authorized_keys If a client key or certificate was presented during authentication, this method returns whether the specified permission is allowed by the corresponding authorized_keys entry. By default, all permissions are granted, but they can be revoked by specifying an option starting with ‘no-‘ without a value. The following standard options are supported: X11-forwarding agent-forwarding port-forwarding pty user-rc AsyncSSH internally enforces X11-forwarding, agent-forwarding, port-forwarding and pty permissions but ignores user-rc since it does not implement that feature. Non-standard permissions can also be checked, as long as the option follows the convention of starting with ‘no-‘. Parameters:permission (str) – The name of the permission to check (without the ‘no-‘). Returns:A bool indicating if the permission is granted.
get_certificate_option(option, default=None) Return option from user certificate If a user certificate was presented during authentication, this method returns the value of the requested option in the certificate if it was set. Otherwise, it returns the default value provided. The following options are supported: force-command (string) source-address (list of CIDR-style IP network addresses) Parameters: option (str) – The name of the option to look up. default – The default value to return if the option is not present. Returns: The value of the option in the user certificate, if set
check_certificate_permission(permission) Check permissions in user certificate If a user certificate was presented during authentication, this method returns whether the specified permission was granted in the certificate. Otherwise, it acts as if all permissions are granted and returns True. The following permissions are supported: X11-forwarding agent-forwarding port-forwarding pty user-rc AsyncSSH internally enforces agent-forwarding, port-forwarding and pty permissions but ignores the other values since it does not implement those features. Parameters:permission (str) – The name of the permission to check (without the ‘permit-‘). Returns:A bool indicating if the permission is granted.

Server connection open methods
create_connection(session_factory, remote_host, remote_port, orig_host='', orig_port=0, *, encoding=None, window=2097152, max_pktsize=32768) Create an SSH TCP forwarded connection This method is a coroutine which can be called to notify the client about a new inbound TCP connection arriving on the specified remote host and port. If the connection is successfully opened, a new SSH channel will be opened with data being handled by a SSHTCPSession object created by session_factory. Optional arguments include the host and port of the original client opening the connection when performing TCP port forwarding. By default, this class expects data to be sent and received as raw bytes. However, an optional encoding argument can be passed in to select the encoding to use, allowing the application send and receive string data. Other optional arguments include the SSH receive window size and max packet size which default to 2 MB and 32 KB, respectively. Parameters: session_factory (callable) – A callable which returns an SSHClientSession object that will be created to handle activity on this session remote_host (str) – The hostname or address the connection was received on remote_port (int) – The port number the connection was received on orig_host (str) – (optional) The hostname or address of the client requesting the connection orig_port (int) – (optional) The port number of the client requesting the connection encoding (str) – (optional) The Unicode encoding to use for data exchanged on the connection window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: an SSHTCPChannel and SSHTCPSession
open_connection(*args, **kwargs) Open an SSH TCP forwarded connection This method is a coroutine wrapper around create_connection() designed to provide a “high-level” stream interface for creating an SSH TCP forwarded connection. Instead of taking a session_factory argument for constructing an object which will handle activity on the session via callbacks, it returns SSHReader and SSHWriter objects which can be used to perform I/O on the connection. With the exception of session_factory, all of the arguments to create_connection() are supported and have the same meaning here. Returns:an SSHReader and SSHWriter
create_unix_connection(session_factory, remote_path, *, encoding=None, window=2097152, max_pktsize=32768) Create an SSH UNIX domain socket forwarded connection This method is a coroutine which can be called to notify the client about a new inbound UNIX domain socket connection arriving on the specified remote path. If the connection is successfully opened, a new SSH channel will be opened with data being handled by a SSHUNIXSession object created by session_factory. By default, this class expects data to be sent and received as raw bytes. However, an optional encoding argument can be passed in to select the encoding to use, allowing the application send and receive string data. Other optional arguments include the SSH receive window size and max packet size which default to 2 MB and 32 KB, respectively. Parameters: session_factory (callable) – A callable which returns an SSHClientSession object that will be created to handle activity on this session remote_path (str) – The path the connection was received on encoding (str) – (optional) The Unicode encoding to use for data exchanged on the connection window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: an SSHTCPChannel and SSHUNIXSession
open_unix_connection(*args, **kwargs) Open an SSH UNIX domain socket forwarded connection This method is a coroutine wrapper around create_unix_connection() designed to provide a “high-level” stream interface for creating an SSH UNIX domain socket forwarded connection. Instead of taking a session_factory argument for constructing an object which will handle activity on the session via callbacks, it returns SSHReader and SSHWriter objects which can be used to perform I/O on the connection. With the exception of session_factory, all of the arguments to create_unix_connection() are supported and have the same meaning here. Returns:an SSHReader and SSHWriter

Server forwarding methods
forward_connection(dest_host, dest_port) Forward a tunneled TCP connection This method is a coroutine which can be returned by a session_factory to forward connections tunneled over SSH to the specified destination host and port. Parameters: dest_host (str) – The hostname or address to forward the connections to dest_port (int) – The port number to forward the connections to Returns: SSHTCPSession
forward_unix_connection(dest_path) Forward a tunneled UNIX domain socket connection This method is a coroutine which can be returned by a session_factory to forward connections tunneled over SSH to the specified destination path. Parameters:dest_path (str) – The path to forward the connection to Returns:SSHUNIXSession

Server channel creation methods
create_server_channel(encoding='utf-8', window=2097152, max_pktsize=32768) Create an SSH server channel for a new SSH session This method can be called by session_requested() to create an SSHServerChannel with the desired encoding, window, and max packet size for a newly created SSH server session. Parameters: encoding (str) – (optional) The Unicode encoding to use for data exchanged on the session, defaulting to UTF-8 (ISO 10646) format. If None is passed in, the application can send and receive raw bytes. window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: SSHServerChannel
create_tcp_channel(encoding=None, window=2097152, max_pktsize=32768) Create an SSH TCP channel for a new direct TCP connection This method can be called by connection_requested() to create an SSHTCPChannel with the desired encoding, window, and max packet size for a newly created SSH direct connection. Parameters: encoding (str) – (optional) The Unicode encoding to use for data exchanged on the connection. This defaults to None, allowing the application to send and receive raw bytes. window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: SSHTCPChannel
create_unix_channel(encoding=None, window=2097152, max_pktsize=32768) Create an SSH UNIX channel for a new direct UNIX domain connection This method can be called by unix_connection_requested() to create an SSHUNIXChannel with the desired encoding, window, and max packet size for a newly created SSH direct UNIX domain socket connection. Parameters: encoding (str) – (optional) The Unicode encoding to use for data exchanged on the connection. This defaults to None, allowing the application to send and receive raw bytes. window (int) – (optional) The receive window size for this session max_pktsize (int) – (optional) The maximum packet size for this session Returns: SSHUNIXChannel

Connection close methods
abort() Forcibly close the SSH connection This method closes the SSH connection immediately, without waiting for pending operations to complete and wihtout sending an explicit SSH disconnect message. Buffered data waiting to be sent will be lost and no more data will be received. When the the connection is closed, connection_lost() on the associated SSHClient object will be called with the value None.
close() Cleanly close the SSH connection This method calls disconnect() with the reason set to indicate that the connection was closed explicitly by the application.
disconnect(code, reason, lang='en-US') Disconnect the SSH connection This method sends a disconnect message and closes the SSH connection after buffered data waiting to be written has been sent. No more data will be received. When the connection is fully closed, connection_lost() on the associated SSHClient or SSHServer object will be called with the value None. Parameters: code (int) – The reason for the disconnect, from disconnect reason codes reason (str) – A human readable reason for the disconnect lang (str) – The language the reason is in
wait_closed() Wait for this connection to close This method is a coroutine which can be called to block until this connection has finished closing.

Process Classes

SSHClientProcess

class asyncssh.SSHClientProcess

SSH client process handler

Process attributes
stdin The SSHWriter to use to write to stdin of the process
stdout The SSHReader to use to read from stdout of the process
stderr The SSHReader to use to read from stderr of the process
exit_status The exit status of the process
exit_signal Exit signal information for the process

I/O redirection methods
redirect_stdin(source, bufsize=8192, send_eof=True) Redirect standard input of the process This method is a coroutine which redirects data from the requested source to standard input of the process. The source can be any of the following: An SSHReader object A file object open for read An int file descriptor open for read A connected socket object A string containing the name of a file or device to open File sources passed in can be associated with plain files, pipes, sockets, or ttys. Parameters: source – Source to feed input from bufsize (int) – Read buffer size to use when forwarding data from a file send_eof (bool) – Whether or not to send EOF to the channel when redirection is complete, defaulting to True. If set to False, multiple sources can be sequentially fed to the channel. The drain method on stdin can be used to determine when redirection is complete.
redirect_stdout(target, bufsize=8192, send_eof=True) Redirect standard output of the process This method is a coroutine which redirects data from standard output of the process to the requested target. The target can be any of the following: An SSHWriter object A file object open for write An int file descriptor open for write A connected socket object A string containing the name of a file or device to open File sources passed in can be associated with plain files, pipes, sockets, or ttys. Parameters: target – Target to feed output to bufsize (int) – Write buffer size to use when forwarding data to a file send_eof (bool) – Whether or not to forward EOF to the target when redirecting to another SSH process, defaulting to True. If set to False, multiple sources can be sequentially fed to the target channel. The drain method on the target can be used to determine when redirection is complete.
redirect_stderr(target, bufsize=8192, send_eof=True) Redirect standard error of the process This method is a coroutine which redirects data from standard error of the process to the requested target. The target can be any of the following: An SSHWriter object A file object open for write An int file descriptor open for write A connected socket object A string containing the name of a file or device to open File sources passed in can be associated with plain files, pipes, sockets, or ttys. Parameters: target – Target to feed output to bufsize (int) – Write buffer size to use when forwarding data to a file send_eof (bool) – Whether or not to forward EOF to the target when redirecting to another SSH process, defaulting to True. If set to False, multiple sources can be sequentially fed to the target channel. The drain method on the target can be used to determine when redirection is complete.

Process communication methods
communicate(input=None) Send input to and/or collect output from the process This method is a coroutine which optionally provides input to the process and then waits for the process to exit, returning a tuple of the data written to stdout and stderr. Parameters:input (str or bytes) – Input data to feed to standard input of the process. Data should be a str if encoding is set, or bytes if not. Returns:A tuple of output to stdout and stderr
change_terminal_size(width, height, pixwidth=0, pixheight=0) Change the terminal window size for this process This method changes the width and height of the terminal associated with this process. Parameters: width (int) – The width of the terminal in characters height (int) – The height of the terminal in characters pixwidth (int) – (optional) The width of the terminal in pixels pixheight (int) – (optional) The height of the terminal in pixels Raises: OSError if the SSH channel is not open
send_break(msec) Send a break to the process Parameters:msec (int) – The duration of the break in milliseconds Raises:OSError if the SSH channel is not open
send_signal(signal) Send a signal to the process Parameters:signal (str) – The signal to deliver Raises:OSError if the SSH channel is not open

Process close methods
terminate() Terminate the process Raises:OSError if the SSH channel is not open
kill() Forcibly kill the process Raises:OSError if the SSH channel is not open
close() Shut down the process
wait(check=False) Wait for process to exit This method is a coroutine which waits for the process to exit. It returns an SSHCompletedProcess object with the exit status or signal information and the output sent to stdout and stderr if those are redirected to pipes. If the check argument is set to True, a non-zero exit status from the process with trigger the ProcessError exception to be raised. Parameters:check (bool) – Whether or not to raise an error on non-zero exit status Returns:SSHCompletedProcess Raises:ProcessError if check is set to True and the process returns a non-zero exit status

SSHCompletedProcess

class asyncssh.SSHCompletedProcess

Results from running an SSH process

This object is returned by the run method on SSHClientConnection when the requested command has finished running. It contains the following fields:

Field	Description	Type
exit_status	The exit status returned, or -1 if an exit signal is sent	int
exit_signal	The exit signal sent (if any) in the form of a tuple containing the signal name, a bool for whether a core dump occurred, a message associated with the signal, and the language the message was in	tuple or None
stdout	The output sent by the process to stdout (if not redirected)	str or bytes
stderr	The output sent by the process to stderr (if not redirected)	str or bytes

Session Classes

SSHClientSession

class asyncssh.SSHClientSession

SSH client session handler

Applications should subclass this when implementing an SSH client session handler. The functions listed below should be implemented to define application-specific behavior. In particular, the standard asyncio protocol methods such as connection_made(), connection_lost(), data_received(), eof_received(), pause_writing(), and resume_writing() are all supported. In addition, session_started() is called as soon as the SSH session is fully started, xon_xoff_requested() can be used to determine if the server wants the client to support XON/XOFF flow control, and exit_status_received() and exit_signal_received() can be used to receive session exit information.

General session handlers
connection_made(chan) Called when a channel is opened successfully This method is called when a channel is opened successfully. The channel parameter should be stored if needed for later use. Parameters:chan (SSHClientChannel) – The channel which was successfully opened.
connection_lost(exc) Called when a channel is closed This method is called when a channel is closed. If the channel is shut down cleanly, exc will be None. Otherwise, it will be an exception explaining the reason for the channel close. Parameters:exc (Exception) – The exception which caused the channel to close, or None if the channel closed cleanly.
session_started() Called when the session is started This method is called when a session has started up. For client and server sessions, this will be called once a shell, exec, or subsystem request has been successfully completed. For TCP and UNIX domain socket sessions, it will be called immediately after the connection is opened.

General session read handlers
data_received(data, datatype) Called when data is received on the channel This method is called when data is received on the channel. If an encoding was specified when the channel was created, the data will be delivered as a string after decoding with the requested encoding. Otherwise, the data will be delivered as bytes. Parameters: data (str or bytes) – The data received on the channel datatype – The extended data type of the data, from extended data types
eof_received() Called when EOF is received on the channel This method is called when an end-of-file indication is received on the channel, after which no more data will be received. If this method returns True, the channel remains half open and data may still be sent. Otherwise, the channel is automatically closed after this method returns. This is the default behavior for classes derived directly from SSHSession, but not when using the higher-level streams API. Because input is buffered in that case, streaming sessions enable half-open channels to allow applications to respond to input read after an end-of-file indication is received.

General session write handlers
pause_writing() Called when the write buffer becomes full This method is called when the channel’s write buffer becomes full and no more data can be sent until the remote system adjusts its window. While data can still be buffered locally, applications may wish to stop producing new data until the write buffer has drained.
resume_writing() Called when the write buffer has sufficiently drained This method is called when the channel’s send window reopens and enough data has drained from the write buffer to allow the application to produce more data.

Other client session handlers
xon_xoff_requested(client_can_do) XON/XOFF flow control has been enabled or disabled This method is called to notify the client whether or not to enable XON/XOFF flow control. If client_can_do is True and output is being sent to an interactive terminal the application should allow input of Control-S and Control-Q to pause and resume output, respectively. If client_can_do is False, Control-S and Control-Q should be treated as normal input and passed through to the server. Non-interactive applications can ignore this request. By default, this message is ignored. Parameters:client_can_do (bool) – Whether or not to enable XON/XOFF flow control
exit_status_received(status) A remote exit status has been received for this session This method is called when the shell, command, or subsystem running on the server terminates and returns an exit status. A zero exit status generally means that the operation was successful. This call will generally be followed by a call to connection_lost(). By default, the exit status is ignored. Parameters:status (int) – The exit status returned by the remote process
exit_signal_received(signal, core_dumped, msg, lang) A remote exit signal has been received for this session This method is called when the shell, command, or subsystem running on the server terminates abnormally with a signal. A more detailed error may also be provided, along with an indication of whether the remote process dumped core. This call will generally be followed by a call to connection_lost(). By default, exit signals are ignored. Parameters: signal (str) – The signal which caused the remote process to exit core_dumped (bool) – Whether or not the remote process dumped core msg – Details about what error occurred lang – The language the error message is in

SSHServerSession

class asyncssh.SSHServerSession

SSH server session handler

Applications should subclass this when implementing an SSH server session handler. The functions listed below should be implemented to define application-specific behavior. In particular, the standard asyncio protocol methods such as connection_made(), connection_lost(), data_received(), eof_received(), pause_writing(), and resume_writing() are all supported. In addition, pty_requested() is called when the client requests a pseudo-terminal, one of shell_requested(), exec_requested(), or subsystem_requested() is called depending on what type of session the client wants to start, session_started() is called once the SSH session is fully started, terminal_size_changed() is called when the client’s terminal size changes, signal_received() is called when the client sends a signal, and break_received() is called when the client sends a break.

General session handlers
connection_made(chan) Called when a channel is opened successfully This method is called when a channel is opened successfully. The channel parameter should be stored if needed for later use. Parameters:chan (SSHClientChannel) – The channel which was successfully opened.
connection_lost(exc) Called when a channel is closed This method is called when a channel is closed. If the channel is shut down cleanly, exc will be None. Otherwise, it will be an exception explaining the reason for the channel close. Parameters:exc (Exception) – The exception which caused the channel to close, or None if the channel closed cleanly.
session_started() Called when the session is started This method is called when a session has started up. For client and server sessions, this will be called once a shell, exec, or subsystem request has been successfully completed. For TCP and UNIX domain socket sessions, it will be called immediately after the connection is opened.

Server session open handlers
pty_requested(term_type, term_size, term_modes) A psuedo-terminal has been requested This method is called when the client sends a request to allocate a pseudo-terminal with the requested terminal type, size, and POSIX terminal modes. This method should return True if the request for the pseudo-terminal is accepted. Otherwise, it should return False to reject the request. By default, requests to allocate a pseudo-terminal are accepted but nothing is done with the associated terminal information. Applications wishing to use this information should implement this method and have it return True, or call get_terminal_type(), get_terminal_size(), or get_terminal_mode() on the SSHServerChannel to get the information they need after a shell, command, or subsystem is started. Parameters: term_type (str) – Terminal type to set for this session term_size (tuple) – Terminal size to set for this session provided as a tuple of four integers: the width and height of the terminal in characters followed by the width and height of the terminal in pixels term_modes (dictionary) – POSIX terminal modes to set for this session, where keys are taken from POSIX terminal modes with values defined in section 8 of RFC 4254#section-8. Returns: A bool indicating if the request for a pseudo-terminal was allowed or not
shell_requested() The client has requested a shell This method should be implemented by the application to perform whatever processing is required when a client makes a request to open an interactive shell. It should return True to accept the request, or False to reject it. If the application returns True, the session_started() method will be called once the channel is fully open. No output should be sent until this method is called. By default this method returns False to reject all requests. Returns:A bool indicating if the shell request was allowed or not
exec_requested(command) The client has requested to execute a command This method should be implemented by the application to perform whatever processing is required when a client makes a request to execute a command. It should return True to accept the request, or False to reject it. If the application returns True, the session_started() method will be called once the channel is fully open. No output should be sent until this method is called. By default this method returns False to reject all requests. Parameters:command (str) – The command the client has requested to execute Returns:A bool indicating if the exec request was allowed or not
subsystem_requested(subsystem) The client has requested to start a subsystem This method should be implemented by the application to perform whatever processing is required when a client makes a request to start a subsystem. It should return True to accept the request, or False to reject it. If the application returns True, the session_started() method will be called once the channel is fully open. No output should be sent until this method is called. By default this method returns False to reject all requests. Parameters:subsystem (str) – The subsystem to start Returns:A bool indicating if the request to open the subsystem was allowed or not

General session read handlers
data_received(data, datatype) Called when data is received on the channel This method is called when data is received on the channel. If an encoding was specified when the channel was created, the data will be delivered as a string after decoding with the requested encoding. Otherwise, the data will be delivered as bytes. Parameters: data (str or bytes) – The data received on the channel datatype – The extended data type of the data, from extended data types
eof_received() Called when EOF is received on the channel This method is called when an end-of-file indication is received on the channel, after which no more data will be received. If this method returns True, the channel remains half open and data may still be sent. Otherwise, the channel is automatically closed after this method returns. This is the default behavior for classes derived directly from SSHSession, but not when using the higher-level streams API. Because input is buffered in that case, streaming sessions enable half-open channels to allow applications to respond to input read after an end-of-file indication is received.

General session write handlers
pause_writing() Called when the write buffer becomes full This method is called when the channel’s write buffer becomes full and no more data can be sent until the remote system adjusts its window. While data can still be buffered locally, applications may wish to stop producing new data until the write buffer has drained.
resume_writing() Called when the write buffer has sufficiently drained This method is called when the channel’s send window reopens and enough data has drained from the write buffer to allow the application to produce more data.

Other server session handlers
break_received(msec) The client has sent a break This method is called when the client requests that the server perform a break operation on the terminal. If the break is performed, this method should return True. Otherwise, it should return False. By default, this method returns False indicating that no break was performed. Parameters:msec (int) – The duration of the break in milliseconds Returns:A bool to indicate if the break operation was performed or not
signal_received(signal) The client has sent a signal This method is called when the client delivers a signal on the channel. By default, signals from the client are ignored.
terminal_size_changed(width, height, pixwidth, pixheight) The terminal size has changed This method is called when a client requests a pseudo-terminal and again whenever the the size of he client’s terminal window changes. By default, this information is ignored, but applications wishing to use the terminal size can implement this method to get notified whenever it changes. Parameters: width (int) – The width of the terminal in characters height (int) – The height of the terminal in characters pixwidth (int) – (optional) The width of the terminal in pixels pixheight (int) – (optional) The height of the terminal in pixels

SSHTCPSession

class asyncssh.SSHTCPSession

SSH TCP session handler

Applications should subclass this when implementing a handler for SSH direct or forwarded TCP connections.

SSH client applications wishing to open a direct connection should call create_connection() on their SSHClientConnection, passing in a factory which returns instances of this class.

Server applications wishing to allow direct connections should implement the coroutine connection_requested() on their SSHServer object and have it return instances of this class.

Server applications wishing to allow connection forwarding back to the client should implement the coroutine server_requested() on their SSHServer object and call create_connection() on their SSHServerConnection for each new connection, passing it a factory which returns instances of this class.

When a connection is successfully opened, session_started() will be called, after which the application can begin sending data. Received data will be passed to the data_received() method.

General session handlers
connection_made(chan) Called when a channel is opened successfully This method is called when a channel is opened successfully. The channel parameter should be stored if needed for later use. Parameters:chan (SSHClientChannel) – The channel which was successfully opened.
connection_lost(exc) Called when a channel is closed This method is called when a channel is closed. If the channel is shut down cleanly, exc will be None. Otherwise, it will be an exception explaining the reason for the channel close. Parameters:exc (Exception) – The exception which caused the channel to close, or None if the channel closed cleanly.
session_started() Called when the session is started This method is called when a session has started up. For client and server sessions, this will be called once a shell, exec, or subsystem request has been successfully completed. For TCP and UNIX domain socket sessions, it will be called immediately after the connection is opened.

General session read handlers
data_received(data, datatype) Called when data is received on the channel This method is called when data is received on the channel. If an encoding was specified when the channel was created, the data will be delivered as a string after decoding with the requested encoding. Otherwise, the data will be delivered as bytes. Parameters: data (str or bytes) – The data received on the channel datatype – The extended data type of the data, from extended data types
eof_received() Called when EOF is received on the channel This method is called when an end-of-file indication is received on the channel, after which no more data will be received. If this method returns True, the channel remains half open and data may still be sent. Otherwise, the channel is automatically closed after this method returns. This is the default behavior for classes derived directly from SSHSession, but not when using the higher-level streams API. Because input is buffered in that case, streaming sessions enable half-open channels to allow applications to respond to input read after an end-of-file indication is received.

General session write handlers
pause_writing() Called when the write buffer becomes full This method is called when the channel’s write buffer becomes full and no more data can be sent until the remote system adjusts its window. While data can still be buffered locally, applications may wish to stop producing new data until the write buffer has drained.
resume_writing() Called when the write buffer has sufficiently drained This method is called when the channel’s send window reopens and enough data has drained from the write buffer to allow the application to produce more data.

SSHUNIXSession

class asyncssh.SSHUNIXSession

SSH UNIX domain socket session handler

Applications should subclass this when implementing a handler for SSH direct or forwarded UNIX domain socket connections.

SSH client applications wishing to open a direct connection should call create_unix_connection() on their SSHClientConnection, passing in a factory which returns instances of this class.

Server applications wishing to allow direct connections should implement the coroutine unix_connection_requested() on their SSHServer object and have it return instances of this class.

Server applications wishing to allow connection forwarding back to the client should implement the coroutine unix_server_requested() on their SSHServer object and call create_unix_connection() on their SSHServerConnection for each new connection, passing it a factory which returns instances of this class.

When a connection is successfully opened, session_started() will be called, after which the application can begin sending data. Received data will be passed to the data_received() method.

General session handlers
connection_made(chan) Called when a channel is opened successfully This method is called when a channel is opened successfully. The channel parameter should be stored if needed for later use. Parameters:chan (SSHClientChannel) – The channel which was successfully opened.
connection_lost(exc) Called when a channel is closed This method is called when a channel is closed. If the channel is shut down cleanly, exc will be None. Otherwise, it will be an exception explaining the reason for the channel close. Parameters:exc (Exception) – The exception which caused the channel to close, or None if the channel closed cleanly.
session_started() Called when the session is started This method is called when a session has started up. For client and server sessions, this will be called once a shell, exec, or subsystem request has been successfully completed. For TCP and UNIX domain socket sessions, it will be called immediately after the connection is opened.

General session read handlers
data_received(data, datatype) Called when data is received on the channel This method is called when data is received on the channel. If an encoding was specified when the channel was created, the data will be delivered as a string after decoding with the requested encoding. Otherwise, the data will be delivered as bytes. Parameters: data (str or bytes) – The data received on the channel datatype – The extended data type of the data, from extended data types
eof_received() Called when EOF is received on the channel This method is called when an end-of-file indication is received on the channel, after which no more data will be received. If this method returns True, the channel remains half open and data may still be sent. Otherwise, the channel is automatically closed after this method returns. This is the default behavior for classes derived directly from SSHSession, but not when using the higher-level streams API. Because input is buffered in that case, streaming sessions enable half-open channels to allow applications to respond to input read after an end-of-file indication is received.

General session write handlers
pause_writing() Called when the write buffer becomes full This method is called when the channel’s write buffer becomes full and no more data can be sent until the remote system adjusts its window. While data can still be buffered locally, applications may wish to stop producing new data until the write buffer has drained.
resume_writing() Called when the write buffer has sufficiently drained This method is called when the channel’s send window reopens and enough data has drained from the write buffer to allow the application to produce more data.

Channel Classes

SSHClientChannel

class asyncssh.SSHClientChannel

SSH client channel

General channel methods

get_extra_info(name, default=None) Get additional information about the channel This method returns extra information about the channel once it is established. Supported values include 'connection' to return the SSH connection this channel is running over plus all of the values supported on that connection. For TCP channels, the values 'local_peername' and 'remote_peername' are added to return the local and remote host and port information for the tunneled TCP connection. For UNIX channels, the values 'local_peername' and 'remote_peername' are added to return the local and remote path information for the tunneled UNIX domain socket connection. Since UNIX domain sockets provide no “source” address, only one of these will be filled in. See get_extra_info() on SSHClientConnection for more information.

Client channel read methods
pause_reading() Pause delivery of incoming data This method is used to temporarily suspend delivery of incoming channel data. After this call, incoming data will no longer be delivered until resume_reading() is called. Data will be buffered locally up to the configured SSH channel window size, but window updates will no longer be sent, eventually causing back pressure on the remote system. Note Channel close notifications are not suspended by this call. If the remote system closes the channel while delivery is suspended, the channel will be closed even though some buffered data may not have been delivered.
resume_reading() Resume delivery of incoming data This method can be called to resume delivery of incoming data which was suspended by a call to pause_reading(). As soon as this method is called, any buffered data will be delivered immediately. A pending end-of-file notication may also be delivered if one was queued while reading was paused.

Client channel write methods
can_write_eof() Return whether the channel supports write_eof() This method always returns True.
get_write_buffer_size() Return the current size of the channel’s output buffer This method returns how many bytes are currently in the channel’s output buffer waiting to be written.
set_write_buffer_limits(high=None, low=None) Set the high- and low-water limits for write flow control This method sets the limits used when deciding when to call the pause_writing() and resume_writing() methods on SSH sessions. Writing will be paused when the write buffer size exceeds the high-water mark, and resumed when the write buffer size equals or drops below the low-water mark.
write(data, datatype=None) Write data on the channel This method can be called to send data on the channel. If an encoding was specified when the channel was created, the data should be provided as a string and will be converted using that encoding. Otherwise, the data should be provided as bytes. An extended data type can optionally be provided. For instance, this is used from a SSHServerSession to write data to stderr. Parameters: data (str or bytes) – The data to send on the channel datatype (int) – (optional) The extended data type of the data, from extended data types Raises: OSError if the channel isn’t open for sending or the extended data type is not valid for this type of channel
writelines(list_of_data, datatype=None) Write a list of data bytes on the channel This method can be called to write a list (or any iterable) of data bytes to the channel. It is functionality equivalent to calling write() on each element in the list. Parameters: list_of_data (iterable of str or bytes objects) – The data to send on the channel datatype (int) – (optional) The extended data type of the data, from extended data types Raises: OSError if the channel isn’t open for sending or the extended data type is not valid for this type of channel
write_eof() Write EOF on the channel This method sends an end-of-file indication on the channel, after which no more data can be sent. The channel remains open, though, and data may still be sent in the other direction. Raises:OSError if the channel isn’t open for sending

Other client channel methods
get_exit_status() Return the session’s exit status This method returns the exit status of the session if one has been sent. If an exit signal was received, this method returns -1 and the exit signal information can be collected by calling get_exit_signal(). If neither has been sent, this method returns None.
get_exit_signal() Return the session’s exit signal, if one was sent This method returns information about the exit signal sent on this session. If an exit signal was sent, a tuple is returned containing the signal name, a boolean for whether a core dump occurred, a message associated with the signal, and the language the message was in. If no exit signal was sent, None is returned.
change_terminal_size(width, height, pixwidth=0, pixheight=0) Change the terminal window size for this session This method changes the width and height of the terminal associated with this session. Parameters: width (int) – The width of the terminal in characters height (int) – The height of the terminal in characters pixwidth (int) – (optional) The width of the terminal in pixels pixheight (int) – (optional) The height of the terminal in pixels
send_break(msec) Send a break to the remote process This method requests that the server perform a break operation on the remote process or service as described in RFC 4335. Parameters:msec (int) – The duration of the break in milliseconds Raises:OSError if the channel is not open
send_signal(signal) Send a signal to the remote process This method can be called to deliver a signal to the remote process or service. Signal names should be as described in section 6.10 of RFC 4254#section-6.10. Parameters:signal (str) – The signal to deliver Raises:OSError if the channel is not open
kill() Forcibly kill the remote process This method can be called to forcibly stop the remote process or service by sending it a KILL signal. Raises:OSError if the channel is not open
terminate() Terminate the remote process This method can be called to terminate the remote process or service by sending it a TERM signal. Raises:OSError if the channel is not open

General channel close methods
abort() Forcibly close the channel This method can be called to forcibly close the channel, after which no more data can be sent or received. Any unsent buffered data and any incoming data in flight will be discarded.
close() Cleanly close the channel This method can be called to cleanly close the channel, after which no more data can be sent or received. Any unsent buffered data will be flushed asynchronously before the channel is closed.
wait_closed() Wait for this channel to close This method is a coroutine which can be called to block until this channel has finished closing.

SSHServerChannel

class asyncssh.SSHServerChannel

SSH server channel

General channel methods

get_extra_info(name, default=None) Get additional information about the channel This method returns extra information about the channel once it is established. Supported values include 'connection' to return the SSH connection this channel is running over plus all of the values supported on that connection. For TCP channels, the values 'local_peername' and 'remote_peername' are added to return the local and remote host and port information for the tunneled TCP connection. For UNIX channels, the values 'local_peername' and 'remote_peername' are added to return the local and remote path information for the tunneled UNIX domain socket connection. Since UNIX domain sockets provide no “source” address, only one of these will be filled in. See get_extra_info() on SSHClientConnection for more information.

Server channel info methods
get_environment() Return the environment for this session This method returns the environment set by the client when the session was opened. Calls to this method should only be made after session_started has been called on the SSHServerSession. Returns:A dictionary containing the environment variables set by the client
get_command() Return the command the client requested to execute, if any This method returns the command the client requested to execute when the session was opened, if any. If the client did not request that a command be executed, this method will return None. Calls to this method should only be made after session_started has been called on the SSHServerSession. When using the stream-based API, calls to this can be made at any time after the handler function has started up.
get_subsystem() Return the subsystem the client requested to open, if any This method returns the subsystem the client requested to open when the session was opened, if any. If the client did not request that a subsystem be opened, this method will return None. Calls to this method should only be made after session_started has been called on the SSHServerSession. When using the stream-based API, calls to this can be made at any time after the handler function has started up.
get_terminal_type() Return the terminal type for this session This method returns the terminal type set by the client when the session was opened. If the client didn’t request a pseudo-terminal, this method will return None. Calls to this method should only be made after session_started has been called on the SSHServerSession. When using the stream-based API, calls to this can be made at any time after the handler function has started up. Returns:A str containing the terminal type or None if no pseudo-terminal was requested
get_terminal_size() Return terminal size information for this session This method returns the latest terminal size information set by the client. If the client didn’t set any terminal size information, all values returned will be zero. Calls to this method should only be made after session_started has been called on the SSHServerSession. When using the stream-based API, calls to this can be made at any time after the handler function has started up. Also see terminal_size_changed() or the TerminalSizeChanged exception for how to get notified when the terminal size changes. Returns:A tuple of four integers containing the width and height of the terminal in characters and the width and height of the terminal in pixels
get_terminal_mode(mode) Return the requested TTY mode for this session This method looks up the value of a POSIX terminal mode set by the client when the session was opened. If the client didn’t request a pseudo-terminal or didn’t set the requested TTY mode opcode, this method will return None. Calls to this method should only be made after session_started has been called on the SSHServerSession. When using the stream-based API, calls to this can be made at any time after the handler function has started up. Parameters:mode (int) – POSIX terminal mode taken from POSIX terminal modes to look up Returns:An int containing the value of the requested POSIX terminal mode or None if the requested mode was not set
get_x11_display() Return the display to use for X11 forwarding When X11 forwarding has been requested by the client, this method returns the X11 display which should be used to open a forwarded connection. If the client did not request X11 forwarding, this method returns None. Returns:A str containing the X11 display or None if X11 fowarding was not requested
get_agent_path() Return the path of the ssh-agent listening socket When agent forwarding has been requested by the client, this method returns the path of the listening socket which should be used to open a forwarded agent connection. If the client did not request agent forwarding, this method returns None. Returns:A str containing the ssh-agent socket path or None if agent fowarding was not requested

Server channel read methods
pause_reading() Pause delivery of incoming data This method is used to temporarily suspend delivery of incoming channel data. After this call, incoming data will no longer be delivered until resume_reading() is called. Data will be buffered locally up to the configured SSH channel window size, but window updates will no longer be sent, eventually causing back pressure on the remote system. Note Channel close notifications are not suspended by this call. If the remote system closes the channel while delivery is suspended, the channel will be closed even though some buffered data may not have been delivered.
resume_reading() Resume delivery of incoming data This method can be called to resume delivery of incoming data which was suspended by a call to pause_reading(). As soon as this method is called, any buffered data will be delivered immediately. A pending end-of-file notication may also be delivered if one was queued while reading was paused.

Server channel write methods
can_write_eof() Return whether the channel supports write_eof() This method always returns True.
get_write_buffer_size() Return the current size of the channel’s output buffer This method returns how many bytes are currently in the channel’s output buffer waiting to be written.
set_write_buffer_limits(high=None, low=None) Set the high- and low-water limits for write flow control This method sets the limits used when deciding when to call the pause_writing() and resume_writing() methods on SSH sessions. Writing will be paused when the write buffer size exceeds the high-water mark, and resumed when the write buffer size equals or drops below the low-water mark.
write(data, datatype=None) Write data on the channel This method can be called to send data on the channel. If an encoding was specified when the channel was created, the data should be provided as a string and will be converted using that encoding. Otherwise, the data should be provided as bytes. An extended data type can optionally be provided. For instance, this is used from a SSHServerSession to write data to stderr. Parameters: data (str or bytes) – The data to send on the channel datatype (int) – (optional) The extended data type of the data, from extended data types Raises: OSError if the channel isn’t open for sending or the extended data type is not valid for this type of channel
writelines(list_of_data, datatype=None) Write a list of data bytes on the channel This method can be called to write a list (or any iterable) of data bytes to the channel. It is functionality equivalent to calling write() on each element in the list. Parameters: list_of_data (iterable of str or bytes objects) – The data to send on the channel datatype (int) – (optional) The extended data type of the data, from extended data types Raises: OSError if the channel isn’t open for sending or the extended data type is not valid for this type of channel
write_stderr(data) Write output to stderr This method can be called to send output to the client which is intended to be displayed on stderr. If an encoding was specified when the channel was created, the data should be provided as a string and will be converted using that encoding. Otherwise, the data should be provided as bytes. Parameters:data (str or bytes) – The data to send to stderr Raises:OSError if the channel isn’t open for sending
writelines_stderr(list_of_data) Write a list of data bytes to stderr This method can be called to write a list (or any iterable) of data bytes to the channel. It is functionality equivalent to calling write_stderr() on each element in the list.
write_eof() Write EOF on the channel This method sends an end-of-file indication on the channel, after which no more data can be sent. The channel remains open, though, and data may still be sent in the other direction. Raises:OSError if the channel isn’t open for sending

Other server channel methods
set_xon_xoff(client_can_do) Set whether the client should enable XON/XOFF flow control This method can be called to tell the client whether or not to enable XON/XOFF flow control, indicating that it should intercept Control-S and Control-Q coming from its local terminal to pause and resume output, respectively. Applications should set client_can_do to True to enable this functionality or to False to tell the client to forward Control-S and Control-Q through as normal input. Parameters:client_can_do (bool) – Whether or not the client should enable XON/XOFF flow control
exit(status) Send exit status and close the channel This method can be called to report an exit status for the process back to the client and close the channel. A zero exit status is generally returned when the operation was successful. After reporting the status, the channel is closed. Parameters:status (int) – The exit status to report to the client Raises:OSError if the channel isn’t open
exit_with_signal(signal, core_dumped=False, msg='', lang='en-US') Send exit signal and close the channel This method can be called to report that the process terminated abnormslly with a signal. A more detailed error message may also provided, along with an indication of whether or not the process dumped core. After reporting the signal, the channel is closed. Parameters: signal (str) – The signal which caused the process to exit core_dumped (bool) – (optional) Whether or not the process dumped core msg (str) – (optional) Details about what error occurred lang (str) – (optional) The language the error message is in Raises: OSError if the channel isn’t open

General channel close methods
abort() Forcibly close the channel This method can be called to forcibly close the channel, after which no more data can be sent or received. Any unsent buffered data and any incoming data in flight will be discarded.
close() Cleanly close the channel This method can be called to cleanly close the channel, after which no more data can be sent or received. Any unsent buffered data will be flushed asynchronously before the channel is closed.
wait_closed() Wait for this channel to close This method is a coroutine which can be called to block until this channel has finished closing.

SSHLineEditorChannel

class asyncssh.SSHLineEditorChannel

Input line editor channel wrapper

When creating server channels with line_editor set to True, this class is wrapped around the channel, providing the caller with the ability to enable and disable input line editing and echoing.

Note

Line editing is only available when a psuedo-terminal is requested on the server channel and the character encoding on the channel is not set to None.

Line editor methods
set_line_mode(line_mode) Enable/disable input line editing This method enabled or disables input line editing. When set, only full lines of input are sent to the session, and each line of input can be edited before it is sent. Parameters:line_mode (bool) – Whether or not to process input a line at a time
set_echo(echo) Enable/disable echoing of input in line mode This method enables or disables echoing of input data when input line editing is enabled. Parameters:echo (bool) – Whether or not input to echo input as it is entered

SSHTCPChannel

class asyncssh.SSHTCPChannel

SSH TCP channel

General channel methods

get_extra_info(name, default=None) Get additional information about the channel This method returns extra information about the channel once it is established. Supported values include 'connection' to return the SSH connection this channel is running over plus all of the values supported on that connection. For TCP channels, the values 'local_peername' and 'remote_peername' are added to return the local and remote host and port information for the tunneled TCP connection. For UNIX channels, the values 'local_peername' and 'remote_peername' are added to return the local and remote path information for the tunneled UNIX domain socket connection. Since UNIX domain sockets provide no “source” address, only one of these will be filled in. See get_extra_info() on SSHClientConnection for more information.

General channel read methods
pause_reading() Pause delivery of incoming data This method is used to temporarily suspend delivery of incoming channel data. After this call, incoming data will no longer be delivered until resume_reading() is called. Data will be buffered locally up to the configured SSH channel window size, but window updates will no longer be sent, eventually causing back pressure on the remote system. Note Channel close notifications are not suspended by this call. If the remote system closes the channel while delivery is suspended, the channel will be closed even though some buffered data may not have been delivered.
resume_reading() Resume delivery of incoming data This method can be called to resume delivery of incoming data which was suspended by a call to pause_reading(). As soon as this method is called, any buffered data will be delivered immediately. A pending end-of-file notication may also be delivered if one was queued while reading was paused.

General channel write methods
can_write_eof() Return whether the channel supports write_eof() This method always returns True.
get_write_buffer_size() Return the current size of the channel’s output buffer This method returns how many bytes are currently in the channel’s output buffer waiting to be written.
set_write_buffer_limits(high=None, low=None) Set the high- and low-water limits for write flow control This method sets the limits used when deciding when to call the pause_writing() and resume_writing() methods on SSH sessions. Writing will be paused when the write buffer size exceeds the high-water mark, and resumed when the write buffer size equals or drops below the low-water mark.
write(data, datatype=None) Write data on the channel This method can be called to send data on the channel. If an encoding was specified when the channel was created, the data should be provided as a string and will be converted using that encoding. Otherwise, the data should be provided as bytes. An extended data type can optionally be provided. For instance, this is used from a SSHServerSession to write data to stderr. Parameters: data (str or bytes) – The data to send on the channel datatype (int) – (optional) The extended data type of the data, from extended data types Raises: OSError if the channel isn’t open for sending or the extended data type is not valid for this type of channel
writelines(list_of_data, datatype=None) Write a list of data bytes on the channel This method can be called to write a list (or any iterable) of data bytes to the channel. It is functionality equivalent to calling write() on each element in the list. Parameters: list_of_data (iterable of str or bytes objects) – The data to send on the channel datatype (int) – (optional) The extended data type of the data, from extended data types Raises: OSError if the channel isn’t open for sending or the extended data type is not valid for this type of channel
write_eof() Write EOF on the channel This method sends an end-of-file indication on the channel, after which no more data can be sent. The channel remains open, though, and data may still be sent in the other direction. Raises:OSError if the channel isn’t open for sending

General channel close methods
abort() Forcibly close the channel This method can be called to forcibly close the channel, after which no more data can be sent or received. Any unsent buffered data and any incoming data in flight will be discarded.
close() Cleanly close the channel This method can be called to cleanly close the channel, after which no more data can be sent or received. Any unsent buffered data will be flushed asynchronously before the channel is closed.
wait_closed() Wait for this channel to close This method is a coroutine which can be called to block until this channel has finished closing.

SSHUNIXChannel

class asyncssh.SSHUNIXChannel

SSH UNIX channel

General channel methods

get_extra_info(name, default=None) Get additional information about the channel This method returns extra information about the channel once it is established. Supported values include 'connection' to return the SSH connection this channel is running over plus all of the values supported on that connection. For TCP channels, the values 'local_peername' and 'remote_peername' are added to return the local and remote host and port information for the tunneled TCP connection. For UNIX channels, the values 'local_peername' and 'remote_peername' are added to return the local and remote path information for the tunneled UNIX domain socket connection. Since UNIX domain sockets provide no “source” address, only one of these will be filled in. See get_extra_info() on SSHClientConnection for more information.

General channel read methods
pause_reading() Pause delivery of incoming data This method is used to temporarily suspend delivery of incoming channel data. After this call, incoming data will no longer be delivered until resume_reading() is called. Data will be buffered locally up to the configured SSH channel window size, but window updates will no longer be sent, eventually causing back pressure on the remote system. Note Channel close notifications are not suspended by this call. If the remote system closes the channel while delivery is suspended, the channel will be closed even though some buffered data may not have been delivered.
resume_reading() Resume delivery of incoming data This method can be called to resume delivery of incoming data which was suspended by a call to pause_reading(). As soon as this method is called, any buffered data will be delivered immediately. A pending end-of-file notication may also be delivered if one was queued while reading was paused.

General channel write methods
can_write_eof() Return whether the channel supports write_eof() This method always returns True.
get_write_buffer_size() Return the current size of the channel’s output buffer This method returns how many bytes are currently in the channel’s output buffer waiting to be written.
set_write_buffer_limits(high=None, low=None) Set the high- and low-water limits for write flow control This method sets the limits used when deciding when to call the pause_writing() and resume_writing() methods on SSH sessions. Writing will be paused when the write buffer size exceeds the high-water mark, and resumed when the write buffer size equals or drops below the low-water mark.
write(data, datatype=None) Write data on the channel This method can be called to send data on the channel. If an encoding was specified when the channel was created, the data should be provided as a string and will be converted using that encoding. Otherwise, the data should be provided as bytes. An extended data type can optionally be provided. For instance, this is used from a SSHServerSession to write data to stderr. Parameters: data (str or bytes) – The data to send on the channel datatype (int) – (optional) The extended data type of the data, from extended data types Raises: OSError if the channel isn’t open for sending or the extended data type is not valid for this type of channel
writelines(list_of_data, datatype=None) Write a list of data bytes on the channel This method can be called to write a list (or any iterable) of data bytes to the channel. It is functionality equivalent to calling write() on each element in the list. Parameters: list_of_data (iterable of str or bytes objects) – The data to send on the channel datatype (int) – (optional) The extended data type of the data, from extended data types Raises: OSError if the channel isn’t open for sending or the extended data type is not valid for this type of channel
write_eof() Write EOF on the channel This method sends an end-of-file indication on the channel, after which no more data can be sent. The channel remains open, though, and data may still be sent in the other direction. Raises:OSError if the channel isn’t open for sending

General channel close methods
abort() Forcibly close the channel This method can be called to forcibly close the channel, after which no more data can be sent or received. Any unsent buffered data and any incoming data in flight will be discarded.
close() Cleanly close the channel This method can be called to cleanly close the channel, after which no more data can be sent or received. Any unsent buffered data will be flushed asynchronously before the channel is closed.
wait_closed() Wait for this channel to close This method is a coroutine which can be called to block until this channel has finished closing.

Listener Classes

SSHListener

class asyncssh.SSHListener

SSH listener for inbound connections

get_port() Return the port number being listened on This method returns the port number that the remote listener was bound to. When the requested remote listening port is 0 to indicate a dynamic port, this method can be called to determine what listening port was selected. This function only applies to TCP listeners. Returns:The port number being listened on
close() Stop listening for new connections This method can be called to stop listening for connections. Existing connections will remain open.
wait_closed() Wait for the listener to close This method is a coroutine which waits for the associated listeners to be closed.

Stream Classes

SSHReader

class asyncssh.SSHReader

SSH read stream handler

channel The SSH channel associated with this stream
get_extra_info(name, default=None) Return additional information about this stream This method returns extra information about the channel associated with this stream. See get_extra_info() on SSHClientChannel for additional information.
at_eof() Return whether the stream is at EOF This method returns True when EOF has been received and all data in the stream has been read.
read(n=-1) Read data from the stream This method is a coroutine which reads up to n bytes or characters from the stream. If n is not provided or set to -1, it reads until EOF or a signal is received. If EOF is received and the receive buffer is empty, an empty bytes or str object is returned. If the next data in the stream is a signal, the signal is delivered as a raised exception. Note Unlike traditional asyncio stream readers, the data will be delivered as either bytes or a str depending on whether an encoding was specified when the underlying channel was opened.
readline() Read one line from the stream This method is a coroutine which reads one line, ending in '\n'. If EOF is received before '\n' is found, the partial line is returned. If EOF is received and the receive buffer is empty, an empty bytes or str object is returned. If the next data in the stream is a signal, the signal is delivered as a raised exception. Note In Python 3.5 and later, SSHReader objects can also be used as async iterators, returning input data one line at a time.
readuntil(separator) Read data from the stream until separator is seen This method is a coroutine which reads from the stream until the requested separator is seen. If a match is found, the returned data will include the separator at the end. If EOF or a signal is received before a match occurs, an IncompleteReadError is raised and its partial attribute will contain the data in the stream prior to the EOF or signal. If the next data in the stream is a signal, the signal is delivered as a raised exception.
readexactly(n) Read an exact amount of data from the stream This method is a coroutine which reads exactly n bytes or characters from the stream. If EOF or a signal is received in the stream before n bytes are read, an IncompleteReadError is raised and its partial attribute will contain the data before the EOF or signal. If the next data in the stream is a signal, the signal is delivered as a raised exception.

SSHWriter

class asyncssh.SSHWriter

SSH write stream handler

channel The SSH channel associated with this stream
get_extra_info(name, default=None) Return additional information about this stream This method returns extra information about the channel associated with this stream. See get_extra_info() on SSHClientChannel for additional information.
can_write_eof() Return whether the stream supports write_eof()
close() Close the channel Note After this is called, no data can be read or written from any of the streams associated with this channel.
drain() Wait until the write buffer on the channel is flushed This method is a coroutine which blocks the caller if the stream is currently paused for writing, returning when enough data has been sent on the channel to allow writing to resume. This can be used to avoid buffering an excessive amount of data in the channel’s send buffer.
write(data) Write data to the stream This method writes bytes or characters to the stream. Note Unlike traditional asyncio stream writers, the data must be supplied as either bytes or a str depending on whether an encoding was specified when the underlying channel was opened.
writelines(list_of_data) Write a collection of data to the stream
write_eof() Write EOF on the channel This method sends an end-of-file indication on the channel, after which no more data can be written. Note On an SSHServerChannel where multiple output streams are created, writing EOF on one stream signals EOF for all of them, since it applies to the channel as a whole.

SFTP Support

SFTPClient

class asyncssh.SFTPClient

SFTP client

This class represents the client side of an SFTP session. It is started by calling the start_sftp_client() method on the SSHClientConnection class.

File transfer methods
get(remotepaths, localpath=None, *, preserve=False, recurse=False, follow_symlinks=False, error_handler=None) Download remote files This method downloads one or more files or directories from the remote system. Either a single remote path or a sequence of remote paths to download can be provided. When downloading a single file or directory, the local path can be either the full path to download data into or the path to an existing directory where the data should be placed. In the latter case, the base file name from the remote path will be used as the local name. When downloading multiple files, the local path must refer to an existing directory. If no local path is provided, the file is downloaded into the current local working directory. If preserve is True, the access and modification times and permissions of the original file are set on the downloaded file. If recurse is True and the remote path points at a directory, the entire subtree under that directory is downloaded. If follow_symlinks is set to True, symbolic links found on the remote system will have the contents of their target downloaded rather than creating a local symbolic link. When using this option during a recursive download, one needs to watch out for links that result in loops. If error_handler is specified and an error occurs during the download, this handler will be called with the exception instead of it being raised. This is intended to primarily be used when multiple remote paths are provided or when recurse is set to True, to allow error information to be collected without aborting the download of the remaining files. The error handler can raise an exception if it wants the download to completely stop. Otherwise, after an error, the download will continue starting with the next file. Parameters: remotepaths (str or bytes, or a sequence of these) – The paths of the remote files or directories to download localpath (str) – (optional) The path of the local file or directory to download into preserve (bool) – (optional) Whether or not to preserve the original file attributes recurse (bool) – (optional) Whether or not to recursively copy directories follow_symlinks (bool) – (optional) Whether or not to follow symbolic links error_handler (callable) – (optional) The function to call when an error occurs Raises: OSError if a local file I/O error occurs SFTPError if the server returns an error
put(localpaths, remotepath=None, *, preserve=False, recurse=False, follow_symlinks=False, error_handler=None) Upload local files This method uploads one or more files or directories to the remote system. Either a single local path or a sequence of local paths to upload can be provided. When uploading a single file or directory, the remote path can be either the full path to upload data into or the path to an existing directory where the data should be placed. In the latter case, the base file name from the local path will be used as the remote name. When uploading multiple files, the remote path must refer to an existing directory. If no remote path is provided, the file is uploaded into the current remote working directory. If preserve is True, the access and modification times and permissions of the original file are set on the uploaded file. If recurse is True and the local path points at a directory, the entire subtree under that directory is uploaded. If follow_symlinks is set to True, symbolic links found on the local system will have the contents of their target uploaded rather than creating a remote symbolic link. When using this option during a recursive upload, one needs to watch out for links that result in loops. If error_handler is specified and an error occurs during the upload, this handler will be called with the exception instead of it being raised. This is intended to primarily be used when multiple local paths are provided or when recurse is set to True, to allow error information to be collected without aborting the upload of the remaining files. The error handler can raise an exception if it wants the upload to completely stop. Otherwise, after an error, the upload will continue starting with the next file. Parameters: localpaths (str or bytes, or a sequence of these) – The paths of the local files or directories to upload remotepath (str or bytes) – (optional) The path of the remote file or directory to upload into preserve (bool) – (optional) Whether or not to preserve the original file attributes recurse (bool) – (optional) Whether or not to recursively copy directories follow_symlinks (bool) – (optional) Whether or not to follow symbolic links error_handler (callable) – (optional) The function to call when an error occurs Raises: OSError if a local file I/O error occurs SFTPError if the server returns an error
copy(srcpaths, dstpath=None, *, preserve=False, recurse=False, follow_symlinks=False, error_handler=None) Copy remote files to a new location This method copies one or more files or directories on the remote system to a new location. Either a single source path or a sequence of source paths to copy can be provided. When copying a single file or directory, the destination path can be either the full path to copy data into or the path to an existing directory where the data should be placed. In the latter case, the base file name from the source path will be used as the destination name. When copying multiple files, the destination path must refer to an existing remote directory. If no destination path is provided, the file is copied into the current remote working directory. If preserve is True, the access and modification times and permissions of the original file are set on the copied file. If recurse is True and the source path points at a directory, the entire subtree under that directory is copied. If follow_symlinks is set to True, symbolic links found in the source will have the contents of their target copied rather than creating a copy of the symbolic link. When using this option during a recursive copy, one needs to watch out for links that result in loops. If error_handler is specified and an error occurs during the copy, this handler will be called with the exception instead of it being raised. This is intended to primarily be used when multiple source paths are provided or when recurse is set to True, to allow error information to be collected without aborting the copy of the remaining files. The error handler can raise an exception if it wants the copy to completely stop. Otherwise, after an error, the copy will continue starting with the next file. Parameters: srcpaths (str or bytes, or a sequence of these) – The paths of the remote files or directories to copy dstpath (str or bytes) – (optional) The path of the remote file or directory to copy into preserve (bool) – (optional) Whether or not to preserve the original file attributes recurse (bool) – (optional) Whether or not to recursively copy directories follow_symlinks (bool) – (optional) Whether or not to follow symbolic links error_handler (callable) – (optional) The function to call when an error occurs Raises: OSError if a local file I/O error occurs SFTPError if the server returns an error
mget(remotepaths, localpath=None, *, preserve=False, recurse=False, follow_symlinks=False, error_handler=None) Download remote files with glob pattern match This method downloads files and directories from the remote system matching one or more glob patterns. The arguments to this method are identical to the get() method, except that the remote paths specified can contain ‘*’ and ‘?’ wildcard characters.
mput(localpaths, remotepath=None, *, preserve=False, recurse=False, follow_symlinks=False, error_handler=None) Upload local files with glob pattern match This method uploads files and directories to the remote system matching one or more glob patterns. The arguments to this method are identical to the put() method, except that the local paths specified can contain ‘*’ and ‘?’ wildcard characters.
mcopy(srcpaths, dstpath=None, *, preserve=False, recurse=False, follow_symlinks=False, error_handler=None) Download remote files with glob pattern match This method copies files and directories on the remote system matching one or more glob patterns. The arguments to this method are identical to the copy() method, except that the source paths specified can contain ‘*’ and ‘?’ wildcard characters.

File access methods
open(path, mode='r', attrs=SFTPAttrs(), encoding='utf-8', errors='strict') Open a remote file This method opens a remote file and returns an SFTPFile object which can be used to read and write data and get and set file attributes. The path can be either a str or bytes value. If it is a str, it will be encoded using the file encoding specified when the SFTPClient was started. The following open mode flags are supported: Mode Description FXF_READ Open the file for reading. FXF_WRITE Open the file for writing. If both this and FXF_READ are set, open the file for both reading and writing. FXF_APPEND Force writes to append data to the end of the file regardless of seek position. FXF_CREAT Create the file if it doesn’t exist. Without this, attempts to open a non-existent file will fail. FXF_TRUNC Truncate the file to zero length if it already exists. FXF_EXCL Return an error when trying to open a file which already exists. By default, file data is read and written as strings in UTF-8 format with strict error checking, but this can be changed using the encoding and errors parameters. To read and write data as bytes in binary format, an encoding value of None can be used. Instead of these flags, a Python open mode string can also be provided. Python open modes map to the above flags as follows: Mode Flags r FXF_READ w FXF_WRITE | FXF_CREAT | FXF_TRUNC a FXF_WRITE | FXF_CREAT | FXF_APPEND x FXF_WRITE | FXF_CREAT | FXF_EXCL r+ FXF_READ | FXF_WRITE w+ FXF_READ | FXF_WRITE | FXF_CREAT | FXF_TRUNC a+ FXF_READ | FXF_WRITE | FXF_CREAT | FXF_APPEND x+ FXF_READ | FXF_WRITE | FXF_CREAT | FXF_EXCL Including a ‘b’ in the mode causes the encoding to be set to None, forcing all data to be read and written as bytes in binary format. The attrs argument is used to set initial attributes of the file if it needs to be created. Otherwise, this argument is ignored. Parameters: path (str or bytes) – The name of the remote file to open pflags_or_mode (int or str) – (optional) The access mode to use for the remote file (see above) attrs (SFTPAttrs) – (optional) File attributes to use if the file needs to be created encoding (str) – (optional) The Unicode encoding to use for data read and written to the remote file errors (str) – (optional) The error-handling mode if an invalid Unicode byte sequence is detected, defaulting to ‘strict’ which raises an exception Returns: An SFTPFile to use to access the file Raises: ValueError if the mode is not valid SFTPError if the server returns an error
truncate(path, size) Truncate a remote file to the specified size This method truncates a remote file to the specified size. If the path provided is a symbolic link, the target of the link will be truncated. Parameters: path (str or bytes) – The path of the remote file to be truncated size (int) – The desired size of the file, in bytes Raises: SFTPError if the server returns an error
rename(oldpath, newpath) Rename a remote file, directory, or link This method renames a remote file, directory, or link. Note This requests the standard SFTP version of rename which will not overwrite the new path if it already exists. To request POSIX behavior where the new path is removed before the rename, use posix_rename(). Parameters: oldpath (str or bytes) – The path of the remote file, directory, or link to rename newpath (str or bytes) – The new name for this file, directory, or link Raises: SFTPError if the server returns an error
posix_rename(oldpath, newpath) Rename a remote file, directory, or link with POSIX semantics This method renames a remote file, directory, or link, removing the prior instance of new path if it previously existed. This method may not be supported by all SFTP servers. Parameters: oldpath (str or bytes) – The path of the remote file, directory, or link to rename newpath (str or bytes) – The new name for this file, directory, or link Raises: SFTPError if the server doesn’t support this extension or returns an error
remove(path) Remove a remote file This method removes a remote file or symbolic link. Parameters:path (str or bytes) – The path of the remote file or link to remove Raises:SFTPError if the server returns an error
unlink(path) Remove a remote file (see remove())
readlink(path) Return the target of a remote symbolic link This method returns the target of a symbolic link. Parameters:path (str or bytes) – The path of the remote symbolic link to follow Returns:The target path of the link as a str or bytes Raises:SFTPError if the server returns an error
symlink(oldpath, newpath) Create a remote symbolic link This method creates a symbolic link. The argument order here matches the standard Python os.symlink() call. The argument order sent on the wire is automatically adapted depending on the version information sent by the server, as a number of servers (OpenSSH in particular) did not follow the SFTP standard when implementing this call. Parameters: oldpath (str or bytes) – The path the link should point to newpath (str or bytes) – The path of where to create the remote symbolic link Raises: SFTPError if the server returns an error
link(oldpath, newpath) Create a remote hard link This method creates a hard link to the remote file specified by oldpath at the location specified by newpath. This method may not be supported by all SFTP servers. Parameters: oldpath (str or bytes) – The path of the remote file the hard link should point to newpath (str or bytes) – The path of where to create the remote hard link Raises: SFTPError if the server doesn’t support this extension or returns an error
realpath(path) Return the canonical version of a remote path This method returns a canonical version of the requested path. Parameters:path (str or bytes) – (optional) The path of the remote directory to canonicalize Returns:The canonical path as a str or bytes, matching the type used to pass in the path Raises:SFTPError if the server returns an error

File attribute access methods
stat(path) Get attributes of a remote file or directory, following symlinks This method queries the attributes of a remote file or directory. If the path provided is a symbolic link, the returned attributes will correspond to the target of the link. Parameters:path (str or bytes) – The path of the remote file or directory to get attributes for Returns:An SFTPAttrs containing the file attributes Raises:SFTPError if the server returns an error
lstat(path) Get attributes of a remote file, directory, or symlink This method queries the attributes of a remote file, directory, or symlink. Unlike stat(), this method returns the attributes of a symlink itself rather than the target of that link. Parameters:path (str or bytes) – The path of the remote file, directory, or link to get attributes for Returns:An SFTPAttrs containing the file attributes Raises:SFTPError if the server returns an error
setstat(path, attrs) Set attributes of a remote file or directory This method sets attributes of a remote file or directory. If the path provided is a symbolic link, the attributes will be set on the target of the link. A subset of the fields in attrs can be initialized and only those attributes will be changed. Parameters: path (str or bytes) – The path of the remote file or directory to set attributes for attrs (SFTPAttrs) – File attributes to set Raises: SFTPError if the server returns an error
statvfs(path) Get attributes of a remote file system This method queries the attributes of the file system containing the specified path. Parameters:path (str or bytes) – The path of the remote file system to get attributes for Returns:An SFTPVFSAttrs containing the file system attributes Raises:SFTPError if the server doesn’t support this extension or returns an error
chown(path, uid, gid) Change the owner user and group id of a remote file or directory This method changes the user and group id of a remote file or directory. If the path provided is a symbolic link, the target of the link will be changed. Parameters: path (str or bytes) – The path of the remote file to change uid (int) – The new user id to assign to the file gid (int) – The new group id to assign to the file Raises: SFTPError if the server returns an error
chmod(path, mode) Change the file permissions of a remote file or directory This method changes the permissions of a remote file or directory. If the path provided is a symbolic link, the target of the link will be changed. Parameters: path (str or bytes) – The path of the remote file to change mode (int) – The new file permissions, expressed as an int Raises: SFTPError if the server returns an error
utime(path, times=None) Change the access and modify times of a remote file or directory This method changes the access and modify times of a remote file or directory. If times is not provided, the times will be changed to the current time. If the path provided is a symbolic link, the target of the link will be changed. Parameters: path (str or bytes) – The path of the remote file to change times (tuple of two int or float values) – (optional) The new access and modify times, as seconds relative to the UNIX epoch Raises: SFTPError if the server returns an error
exists(path) Return if the remote path exists and isn’t a broken symbolic link Parameters:path (str or bytes) – The remote path to check Raises:SFTPError if the server returns an error
lexists(path) Return if the remote path exists, without following symbolic links Parameters:path (str or bytes) – The remote path to check Raises:SFTPError if the server returns an error
getatime(path) Return the last access time of a remote file or directory Parameters:path (str or bytes) – The remote path to check Raises:SFTPError if the server returns an error
getmtime(path) Return the last modification time of a remote file or directory Parameters:path (str or bytes) – The remote path to check Raises:SFTPError if the server returns an error
getsize(path) Return the size of a remote file or directory Parameters:path (str or bytes) – The remote path to check Raises:SFTPError if the server returns an error
isdir(path) Return if the remote path refers to a directory Parameters:path (str or bytes) – The remote path to check Raises:SFTPError if the server returns an error
isfile(path) Return if the remote path refers to a regular file Parameters:path (str or bytes) – The remote path to check Raises:SFTPError if the server returns an error
islink(path) Return if the remote path refers to a symbolic link Parameters:path (str or bytes) – The remote path to check Raises:SFTPError if the server returns an error

Directory access methods
chdir(path) Change the current remote working directory Parameters:path (str or bytes) – The path to set as the new remote working directory Raises:SFTPError if the server returns an error
getcwd() Return the current remote working directory Returns:The current remote working directory, decoded using the specified path encoding Raises:SFTPError if the server returns an error
mkdir(path, attrs=SFTPAttrs()) Create a remote directory with the specified attributes This method creates a new remote directory at the specified path with the requested attributes. Parameters: path (str or bytes) – The path of where the new remote directory should be created attrs (SFTPAttrs) – (optional) The file attributes to use when creating the directory Raises: SFTPError if the server returns an error
rmdir(path) Remove a remote directory This method removes a remote directory. The directory must be empty for the removal to succeed. Parameters:path (str or bytes) – The path of the remote directory to remove Raises:SFTPError if the server returns an error
readdir(path='.') Read the contents of a remote directory This method reads the contents of a directory, returning the names and attributes of what is contained there. If no path is provided, it defaults to the current remote working directory. Parameters:path (str or bytes) – (optional) The path of the remote directory to read Returns:A list of SFTPName entries, with path names matching the type used to pass in the path Raises:SFTPError if the server returns an error
listdir(path='.') Read the names of the files in a remote directory This method reads the names of files and subdirectories in a remote directory. If no path is provided, it defaults to the current remote working directory. Parameters:path (str or bytes) – (optional) The path of the remote directory to read Returns:A list of file/subdirectory names, matching the type used to pass in the path Raises:SFTPError if the server returns an error
glob(patterns, error_handler=None) Match remote files against glob patterns This method matches remote files against one or more glob patterns. Either a single pattern or a sequence of patterns can be provided to match against. If error_handler is specified and an error occurs during the match, this handler will be called with the exception instead of it being raised. This is intended to primarily be used when multiple patterns are provided to allow error information to be collected without aborting the match against the remaining patterns. The error handler can raise an exception if it wants to completely abort the match. Otherwise, after an error, the match will continue starting with the next pattern. An error will be raised if any of the patterns completely fail to match, and this can either stop the match against the remaining patterns or be handled by the error_handler just like other errors. Parameters: patterns (str or bytes, or a sequence of these) – Glob patterns to try and match remote files against error_handler (callable) – (optional) The function to call when an error occurs Raises: SFTPError if the server returns an error or no match is found

Cleanup methods
exit() Exit the SFTP client session This method exits the SFTP client session, closing the corresponding channel opened on the server.
wait_closed() Wait for this SFTP client session to close

SFTPServer

class asyncssh.SFTPServer(conn, chroot=None)

SFTP server

Applications should subclass this when implementing an SFTP server. The methods listed below should be implemented to provide the desired application behavior.

Note

Any method can optionally be defined as a coroutine if that method needs to perform blocking opertions to determine its result.

The conn object provided here refers to the SSHServerConnection instance this SFTP server is associated with. It can be queried to determine which user the client authenticated as or to request key and certificate options or permissions which should be applied to this session.

If the chroot argument is specified when this object is created, the default map_path() and reverse_map_path() methods will enforce a virtual root directory starting in that location, limiting access to only files within that directory tree. This will also affect path names returned by the realpath() and readlink() methods.

Path remapping and display methods
format_longname(name) Format the long name associated with an SFTP name This method fills in the longname field of a SFTPName object. By default, it generates something similar to UNIX “ls -l” output. The filename and attrs fields of the SFTPName should already be filled in before this method is called. Parameters:name (SFTPName) – The SFTPName instance to format the long name for
map_path(path) Map the path requested by the client to a local path This method can be overridden to provide a custom mapping from path names requested by the client to paths in the local filesystem. By default, it will enforce a virtual “chroot” if one was specified when this server was created. Otherwise, path names are left unchanged, with relative paths being interpreted based on the working directory of the currently running process. Parameters:path (bytes) – The path name to map Returns:bytes containing he local path name to operate on
reverse_map_path(path) Reverse map a local path into the path reported to the client This method can be overridden to provide a custom reverse mapping for the mapping provided by map_path(). By default, it hides the portion of the local path associated with the virtual “chroot” if one was specified. Parameters:path (bytes) – The local path name to reverse map Returns:bytes containing the path name to report to the client

File access methods
open(path, pflags, attrs) Open a file to serve to a remote client This method returns a file object which can be used to read and write data and get and set file attributes. The possible open mode flags and their meanings are: Mode Description FXF_READ Open the file for reading. If neither FXF_READ nor FXF_WRITE are set, this is the default. FXF_WRITE Open the file for writing. If both this and FXF_READ are set, open the file for both reading and writing. FXF_APPEND Force writes to append data to the end of the file regardless of seek position. FXF_CREAT Create the file if it doesn’t exist. Without this, attempts to open a non-existent file will fail. FXF_TRUNC Truncate the file to zero length if it already exists. FXF_EXCL Return an error when trying to open a file which already exists. The attrs argument is used to set initial attributes of the file if it needs to be created. Otherwise, this argument is ignored. Parameters: path (bytes) – The name of the file to open pflags (int) – The access mode to use for the file (see above) attrs (SFTPAttrs) – File attributes to use if the file needs to be created Returns: A file object to use to access the file Raises: SFTPError to return an error to the client
close(file_obj) Close an open file or directory Parameters:file_obj (file) – The file or directory object to close Raises:SFTPError to return an error to the client
read(file_obj, offset, size) Read data from an open file Parameters: file_obj (file) – The file to read from offset (int) – The offset from the beginning of the file to begin reading size (int) – The number of bytes to read Returns: bytes read from the file Raises: SFTPError to return an error to the client
write(file_obj, offset, data) Write data to an open file Parameters: file_obj (file) – The file to write to offset (int) – The offset from the beginning of the file to begin writing data (bytes) – The data to write to the file Returns: number of bytes written Raises: SFTPError to return an error to the client
rename(oldpath, newpath) Rename a file, directory, or link This method renames a file, directory, or link. Note This is a request for the standard SFTP version of rename which will not overwrite the new path if it already exists. The posix_rename() method will be called if the client requests the POSIX behavior where an existing instance of the new path is removed before the rename. Parameters: oldpath (bytes) – The path of the file, directory, or link to rename newpath (bytes) – The new name for this file, directory, or link Raises: SFTPError to return an error to the client
posix_rename(oldpath, newpath) Rename a file, directory, or link with POSIX semantics This method renames a file, directory, or link, removing the prior instance of new path if it previously existed. Parameters: oldpath (bytes) – The path of the file, directory, or link to rename newpath (bytes) – The new name for this file, directory, or link Raises: SFTPError to return an error to the client
remove(path) Remove a file or symbolic link Parameters:path (bytes) – The path of the file or link to remove Raises:SFTPError to return an error to the client
readlink(path) Return the target of a symbolic link Parameters:path (bytes) – The path of the symbolic link to follow Returns:bytes containing the target path of the link Raises:SFTPError to return an error to the client
symlink(oldpath, newpath) Create a symbolic link Parameters: oldpath (bytes) – The path the link should point to newpath (bytes) – The path of where to create the symbolic link Raises: SFTPError to return an error to the client
link(oldpath, newpath) Create a hard link Parameters: oldpath (bytes) – The path of the file the hard link should point to newpath (bytes) – The path of where to create the hard link Raises: SFTPError to return an error to the client
realpath(path) Return the canonical version of a path Parameters:path (bytes) – The path of the directory to canonicalize Returns:bytes containing the canonical path Raises:SFTPError to return an error to the client

File attribute access methods
stat(path) Get attributes of a file or directory, following symlinks This method queries the attributes of a file or directory. If the path provided is a symbolic link, the returned attributes should correspond to the target of the link. Parameters:path (bytes) – The path of the remote file or directory to get attributes for Returns:An SFTPAttrs or an os.stat_result containing the file attributes Raises:SFTPError to return an error to the client
lstat(path) Get attributes of a file, directory, or symlink This method queries the attributes of a file, directory, or symlink. Unlike stat(), this method should return the attributes of a symlink itself rather than the target of that link. Parameters:path (bytes) – The path of the file, directory, or link to get attributes for Returns:An SFTPAttrs or an os.stat_result containing the file attributes Raises:SFTPError to return an error to the client
fstat(file_obj) Get attributes of an open file Parameters:file_obj (file) – The file to get attributes for Returns:An SFTPAttrs or an os.stat_result containing the file attributes Raises:SFTPError to return an error to the client
setstat(path, attrs) Set attributes of a file or directory This method sets attributes of a file or directory. If the path provided is a symbolic link, the attributes should be set on the target of the link. A subset of the fields in attrs can be initialized and only those attributes should be changed. Parameters: path (bytes) – The path of the remote file or directory to set attributes for attrs (SFTPAttrs) – File attributes to set Raises: SFTPError to return an error to the client
fsetstat(file_obj, attrs) Set attributes of an open file Parameters:attrs (SFTPAttrs) – File attributes to set on the file Raises:SFTPError to return an error to the client
statvfs(path) Get attributes of the file system containing a file Parameters:path (bytes) – The path of the file system to get attributes for Returns:An SFTPVFSAttrs or an os.statvfs_result containing the file system attributes Raises:SFTPError to return an error to the client
fstatvfs(file_obj) Return attributes of the file system containing an open file Parameters:file_obj (file) – The open file to get file system attributes for Returns:An SFTPVFSAttrs or an os.statvfs_result containing the file system attributes Raises:SFTPError to return an error to the client

Directory access methods
listdir(path) List the contents of a directory Parameters:path (bytes) – The path of the directory to open Returns:A list of names of files in the directory Raises:SFTPError to return an error to the client
mkdir(path, attrs) Create a directory with the specified attributes Parameters: path (bytes) – The path of where the new directory should be created attrs (SFTPAttrs) – The file attributes to use when creating the directory Raises: SFTPError to return an error to the client
rmdir(path) Remove a directory Parameters:path (bytes) – The path of the directory to remove Raises:SFTPError to return an error to the client

Cleanup methods
exit() Shut down this SFTP server

SFTPFile

class asyncssh.SFTPFile

SFTP client remote file object

This class represents an open file on a remote SFTP server. It is opened with the open() method on the SFTPClient class and provides methods to read and write data and get and set attributes on the open file.

read(size=-1, offset=None) Read data from the remote file This method reads and returns up to size bytes of data from the remote file. If size is negative, all data up to the end of the file is returned. If offset is specified, the read will be performed starting at that offset rather than the current file position. This argument should be provided if you want to issue parallel reads on the same file, since the file position is not predictable in that case. Data will be returned as a string if an encoding was set when the file was opened. Otherwise, data is returned as bytes. An empty string or bytes object is returned when at EOF. Parameters: size (int) – The number of bytes to read offset (int) – (optional) The offset from the beginning of the file to begin reading Returns: data read from the file, as a str or bytes Raises: ValueError if the file has been closed UnicodeDecodeError if the data can’t be decoded using the requested encoding SFTPError if the server returns an error
write(data, offset=None) Write data to the remote file This method writes the specified data at the current position in the remote file. Parameters: data (str or bytes) – The data to write to the file offset (int) – (optional) The offset from the beginning of the file to begin writing If offset is specified, the write will be performed starting at that offset rather than the current file position. This argument should be provided if you want to issue parallel writes on the same file, since the file position is not predictable in that case. Returns:number of bytes written Raises: ValueError if the file has been closed UnicodeEncodeError if the data can’t be encoded using the requested encoding SFTPError if the server returns an error
seek(offset, from_what=SEEK_SET) Seek to a new position in the remote file This method changes the position in the remote file. The offset passed in is treated as relative to the beginning of the file if from_what is set to SEEK_SET (the default), relative to the current file position if it is set to SEEK_CUR, or relative to the end of the file if it is set to SEEK_END. Parameters: offset (int) – The amount to seek from_what (int) – (optional) The reference point to use (SEEK_SET, SEEK_CUR, or SEEK_END) Returns: The new byte offset from the beginning of the file
tell() Return the current position in the remote file This method returns the current position in the remote file. Returns:The current byte offset from the beginning of the file
stat() Return file attributes of the remote file This method queries file attributes of the currently open file. Returns:An SFTPAttrs containing the file attributes Raises:SFTPError if the server returns an error
setstat(attrs) Set attributes of the remote file This method sets file attributes of the currently open file. Parameters:attrs (SFTPAttrs) – File attributes to set on the file Raises:SFTPError if the server returns an error
statvfs() Return file system attributes of the remote file This method queries attributes of the file system containing the currently open file. Returns:An SFTPVFSAttrs containing the file system attributes Raises:SFTPError if the server doesn’t support this extension or returns an error
truncate(size=None) Truncate the remote file to the specified size This method changes the remote file’s size to the specified value. If a size is not provided, the current file position is used. Parameters:size (int) – (optional) The desired size of the file, in bytes Raises:SFTPError if the server returns an error
chown(uid, gid) Change the owner user and group id of the remote file This method changes the user and group id of the currently open file. Parameters: uid (int) – The new user id to assign to the file gid (int) – The new group id to assign to the file Raises: SFTPError if the server returns an error
chmod(mode) Change the file permissions of the remote file This method changes the permissions of the currently open file. Parameters:mode (int) – The new file permissions, expressed as an int Raises:SFTPError if the server returns an error
utime(times=None) Change the access and modify times of the remote file This method changes the access and modify times of the currently open file. If times is not provided, the times will be changed to the current time. Parameters:times (tuple of two int or float values) – (optional) The new access and modify times, as seconds relative to the UNIX epoch Raises:SFTPError if the server returns an error
fsync() Force the remote file data to be written to disk
close() Close the remote file

SFTPAttrs

class asyncssh.SFTPAttrs

SFTP file attributes

SFTPAttrs is a simple record class with the following fields:

Field	Description	Type
size	File size in bytes	uint64
uid	User id of file owner	uint32
gid	Group id of file owner	uint32
permissions	Bit mask of POSIX file permissions,	uint32
atime	Last access time, UNIX epoch seconds	uint32
mtime	Last modification time, UNIX epoch seconds	uint32

In addition to the above, an nlink field is provided which stores the number of links to this file, but it is not encoded in the SFTP protocol. It’s included here only so that it can be used to create the default longname string in SFTPName objects.

Extended attributes can also be added via a field named extended which is a list of string name/value pairs.

When setting attributes using an SFTPAttrs, only fields which have been initialized will be changed on the selected file.

SFTPVFSAttrs

class asyncssh.SFTPVFSAttrs

SFTP file system attributes

SFTPVFSAttrs is a simple record class with the following fields:

Field	Description	Type
bsize	File system block size (I/O size)	uint64
frsize	Fundamental block size (allocation size)	uint64
blocks	Total data blocks (in frsize units)	uint64
bfree	Free data blocks	uint64
bavail	Available data blocks (for non-root)	uint64
files	Total file inodes	uint64
ffree	Free file inodes	uint64
favail	Available file inodes (for non-root)	uint64
fsid	File system id	uint64
flags	File system flags (read-only, no-setuid)	uint64
namemax	Maximum filename length	uint64

SFTPName

class asyncssh.SFTPName

SFTP file name and attributes

SFTPName is a simple record class with the following fields:

Field	Description	Type
filename	Filename	str or bytes
longname	Expanded form of filename & attrs	str or bytes
attrs	File attributes	SFTPAttrs

A list of these is returned by readdir() in SFTPClient when retrieving the contents of a directory.

Public Key Support

AsyncSSH has extensive public key and certificate support.

Supported public key types include DSA, RSA, and ECDSA. In addition, Ed25519 keys are supported if the libnacl package and libsodium library are installed.

Supported certificate types include OpenSSH version 01 certificates for DSA, RSA, ECDSA, and Ed25519 keys. Support is also available for the certificate critical options of force-command and source-address and the extensions permit-X11-forwarding, permit-agent-forwarding, permit-port-forwarding, and permit-pty.

Several public key and certificate formats are supported including PKCS#1 and PKCS#8 DER and PEM, OpenSSH, and RFC4716 formats.

PEM and PKCS#8 password-based encryption of private keys is supported, as is OpenSSH private key encryption when the bcrypt package is installed.

Specifying private keys

Private keys may be passed into AsyncSSH in a variety of forms. The simplest option is to pass the name of a file to read one or more private keys from.

An alternate form involves passing in a list of values which can be either a reference to a private key or a tuple containing a reference to a private key and a reference to a matching certificate.

Key references can either be the name of a file to load a key from, a byte string to import as a key, or an already loaded SSHKey private key. See the function import_private_key() for the list of supported private key formats.

Certificate references can be the name of a file to load the certificate from, a byte string to import as a certificate, an already loaded SSHCertificate, or None if no certificate should be associated with the key.

Whenever a filename is provided, an attempt is made to load a corresponding certificate from a file constructed by appending ‘-cert.pub’ to the end of the name.

New private keys can be generated using the generate_private_key() function. The resulting SSHKey objects have methods which can then be used to export the generated keys in several formats for consumption by other tools.

Specifying public keys

Public keys may be passed into AsyncSSH in a variety of forms. The simplest option is to pass the name of a file to read one or more public keys from.

An alternate form involves passing in a list of values each of which can be either the name of a file to load a key from, a byte string to import it from, or an already loaded SSHKey public key. See the function import_public_key() for the list of supported public key formats.

Specifying time values

When generating certificates, an optional validity interval can be specified using the valid_after and valid_before parameters to the generate_user_certificate() and generate_host_certificate() methods. These values can be specified in any of the following ways:

• An int or float UNIX epoch time, such as what is returned by time.time().
• A datetime.datetime value.
• A string value of now to request the current time.
• A string value in the form YYYYMMDD to specify an absolute date.
• A string value in the form YYYYMMDDHHMMSS to specify an absolute date and time.
• A relative time made up of a mix of positive or negative numbers and the letters ‘w’, ‘d’, ‘h’, ‘m’, and ‘s’, representing an offset from the current time in weeks, days, hours, minutes, or seconds, respectively. Multiple of these values can be included. For instance, ‘+1w2d3h’ means 1 week, 2 days, and 3 hours in the future.

SSHKey

class asyncssh.SSHKey

Parent class which holds an asymmetric encryption key

get_algorithm() Return the algorithm associated with this key
get_comment() Return the comment associated with this key Returns:str or None
set_comment(comment) Set the comment associated with this key Parameters:comment (str or None) – The new comment to associate with this key
convert_to_public() Return public key corresponding to this key This method converts an SSHKey object which contains a private key into one which contains only the corresponding public key. If it is called on something which is already a public key, it has no effect.
generate_user_certificate(user_key, key_id, version=1, serial=0, principals=(), valid_after=0, valid_before=18446744073709551615, force_command=None, source_address=None, permit_x11_forwarding=True, permit_agent_forwarding=True, permit_port_forwarding=True, permit_pty=True, permit_user_rc=True, comment=()) Generate a new SSH user certificate This method returns a SSH user certifcate with the requested attributes signed by this private key. Parameters: user_key (SSHKey) – The user’s public key. key_id (str) – The key identifier associated with this certificate. version (int) – (optional) The version of certificate to create, defaulting to 1. serial (int) – (optional) The serial number of the certificate, defaulting to 0. principals (list of strings) – (optional) The user names this certificate is valid for. By default, it can be used with any user name. valid_after – (optional) The earliest time the certificate is valid for, defaulting to no restriction on when the certificate starts being valid. See Specifying time values for allowed time specifications. valid_before – (optional) The latest time the certificate is valid for, defaulting to no restriction on when the certificate stops being valid. See Specifying time values for allowed time specifications. force_command (str or None) – (optional) The command (if any) to force a session to run when this certificate is used. source_address (list of ip_address and ip_network values) – (optional) A list of source addresses and networks for which the certificate is valid, defaulting to all addresses. permit_x11_forwarding (bool) – (optional) Whether or not to allow this user to use X11 forwarding, defaulting to True. permit_agent_forwarding (bool) – (optional) Whether or not to allow this user to use agent forwarding, defaulting to True. permit_port_forwarding (bool) – (optional) Whether or not to allow this user to use port forwarding, defaulting to True. permit_pty (bool) – (optional) Whether or not to allow this user to allocate a pseudo-terminal, defaulting to True. permit_user_rc (bool) – (optional) Whether or not to run the user rc file when this certificate is used, defaulting to True. comment (str or None) – The comment to associate with this certificate. By default, the comment will be set to the comment currently set on user_key. Returns: SSHCertificate Raises: ValueError if the validity times are invalid KeyGenerationError if the requested certificate parameters are unsupported
generate_host_certificate(host_key, key_id, version=1, serial=0, principals=(), valid_after=0, valid_before=18446744073709551615, comment=()) Generate a new SSH host certificate This method returns a SSH host certifcate with the requested attributes signed by this private key. Parameters: host_key (SSHKey) – The host’s public key. key_id (str) – The key identifier associated with this certificate. version (int) – (optional) The version of certificate to create, defaulting to 1. serial (int) – (optional) The serial number of the certificate, defaulting to 0. principals (list of strings) – (optional) The host names this certificate is valid for. By default, it can be used with any host name. valid_after – (optional) The earliest time the certificate is valid for, defaulting to no restriction on when the certificate starts being valid. See Specifying time values for allowed time specifications. valid_before – (optional) The latest time the certificate is valid for, defaulting to no restriction on when the certificate stops being valid. See Specifying time values for allowed time specifications. comment (str or None) – The comment to associate with this certificate. By default, the comment will be set to the comment currently set on host_key. Returns: SSHCertificate Raises: ValueError if the validity times are invalid KeyGenerationError if the requested certificate parameters are unsupported
export_private_key(format_name='openssh', passphrase=None, cipher_name='aes256-cbc', hash_name='sha256', pbe_version=2, rounds=16) Export a private key in the requested format This method returns this object’s private key encoded in the requested format. If a passphrase is specified, the key will be exported in encrypted form. Available formats include: pkcs1-der, pkcs1-pem, pkcs8-der, pkcs8-pem, openssh By default, openssh format will be used. Encryption is supported in pkcs1-pem, pkcs8-der, pkcs8-pem, and openssh formats. For pkcs1-pem, only the cipher can be specified. For pkcs8-der and pkcs-8, cipher, hash and PBE version can be specified. For openssh, cipher and rounds can be specified. Available ciphers for pkcs1-pem are: aes128-cbc, aes192-cbc, aes256-cbc, des-cbc, des3-cbc Available ciphers for pkcs8-der and pkcs8-pem are: aes128-cbc, aes192-cbc, aes256-cbc, blowfish-cbc, cast128-cbc, des-cbc, des2-cbc, des3-cbc, rc4-40, rc4-128 Available ciphers for openssh format include the following encryption algorithms. Available hashes include: md5, sha1, sha256, sha384, sha512, sha512-224, sha512-256 Available PBE versions include 1 for PBES1 and 2 for PBES2. Not all combinations of cipher, hash, and version are supported. The default cipher is aes256. In the pkcs8 formats, the default hash is sha256 and default version is PBES2. In openssh format, the default number of rounds is 16. Parameters: format_name (str) – (optional) The format to export the key in. passphrase (str) – (optional) A passphrase to encrypt the private key with. cipher_name (str) – (optional) The cipher to use for private key encryption. hash_name (str) – (optional) The hash to use for private key encryption. pbe_version (int) – (optional) The PBE version to use for private key encryption. rounds (int) – (optional) The number of KDF rounds to apply to the passphrase. Returns: bytes representing the exported private key
export_public_key(format_name='openssh') Export a public key in the requested format This method returns this object’s public key encoded in the requested format. Available formats include: pkcs1-der, pkcs1-pem, pkcs8-der, pkcs8-pem, openssh, rfc4716 By default, openssh format will be used. Parameters:format_name (str) – (optional) The format to export the key in. Returns:bytes representing the exported public key
write_private_key(filename, *args, **kwargs) Write a private key to a file in the requested format This method is a simple wrapper around export_private_key() which writes the exported key data to a file. Parameters: filename (str) – The filename to write the private key to. *args,**kwargs – Additional arguments to pass through to export_private_key().
write_public_key(filename, *args, **kwargs) Write a public key to a file in the requested format This method is a simple wrapper around export_public_key() which writes the exported key data to a file. Parameters: filename (str) – The filename to write the public key to. *args,**kwargs – Additional arguments to pass through to export_public_key().

SSHKeyPair

class asyncssh.SSHKeyPair

Parent class which represents an asymmetric key pair

This is an abstract class which provides a method to sign data with a private key and members to access the corresponding algorithm and public key or certificate information needed to identify what key was used for signing.

get_key_type() Return what type of key pair this is This method returns ‘local’ for locally loaded keys, and ‘agent’ for keys managed by an SSH agent.
get_algorithm() Return the algorithm associated with this key pair
get_comment() Return the comment associated with this key pair Returns:str or None
set_comment(comment) Set the comment associated with this key pair Parameters:comment (str or None) – The new comment to associate with this key pair
sign(data) Sign a block of data with this private key Parameters:data (str) – The data to be signed. Returns:bytes containing the signature.

SSHCertificate

class asyncssh.SSHCertificate

Parent class which holds an SSH certificate

get_algorithm() Return the algorithm associated with this certificate
get_comment() Return the comment associated with this certificate Returns:str or None
set_comment(comment) Set the comment associated with this certificate Parameters:comment (str or None) – The new comment to associate with this certificate
export_certificate(format_name='openssh') Export a certificate in the requested format This function returns this certificate encoded in the requested format. Available formats include: openssh, rfc4716 By default, openssh format will be used. Parameters:format_name (str) – (optional) The format to export the certificate in. Returns:bytes representing the exported certificate
write_certificate(filename, *args, **kwargs) Write a certificate to a file in the requested format This function is a simple wrapper around export_certificate which writes the exported certificate to a file. Parameters: filename (str) – The filename to write the certificate to. *args,**kwargs – Additional arguments to pass through to export_certificate().
validate(cert_type, principal) Validate the certificate type, validity period, and principal This method validates that the certificate is of the specified type, that the current time is within the certificate validity period, and that the principal being authenticated is one of the certificate’s valid principals. Parameters: cert_type (int) – The expected certificate type. principal (str) – The principal being authenticated. Raises: ValueError if any of the validity checks fail

generate_private_key

asyncssh.generate_private_key(alg_name, comment=None, **kwargs)

Generate a new private key

This function generates a new private key of a type matching the requested SSH algorithm. Depending on the algorithm, additional parameters can be passed which affect the generated key.

Available algorithms include:

ssh-dss, ssh-rsa, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, ssh-ed25519

For ssh-dss, no parameters are supported. The key size is fixed at 1024 bits due to the use of SHA1 signatures.

For ssh-rsa, the key size can be specified using the key_size parameter, and the RSA public exponent can be changed using the exponent parameter. By default, generated keys are 2048 bits with a public exponent of 65537.

For ecdsa, the curve to use is part of the SSH algorithm name and that determines the key size. No other parameters are supported.

For ssh-ed25519, no parameters are supported. The key size is fixed by the algorithm at 256 bits.

Parameters:

• alg_name (str) – The SSH algorithm name corresponding to the desired type of key.
• comment (str or None) – (optional) A comment to associate with this key.
• key_size (int) – (optional) The key size in bits for RSA keys.
• exponent (int) – (optional) The public exponent for RSA keys.

Returns:

An SSHKey private key

Raises:

KeyGenerationError if the requested key parameters are unsupported

import_private_key

asyncssh.import_private_key(data, passphrase=None)

Import a private key

This function imports a private key encoded in PKCS#1 or PKCS#8 DER or PEM format or OpenSSH format. Encrypted private keys can be imported by specifying the passphrase needed to decrypt them.

Parameters:

• data (bytes or ASCII string) – The data to import.
• passphrase (str) – (optional) The passphrase to use to decrypt the key.

Returns:

An SSHKey private key

import_public_key

asyncssh.import_public_key(data)

Import a public key

This function imports a public key encoded in OpenSSH, RFC4716, or PKCS#1 or PKCS#8 DER or PEM format.

Parameters:data (bytes or ASCII string) – The data to import. Returns:An SSHKey public key

import_certificate

asyncssh.import_certificate(data)

Import a certificate

This function imports an SSH certificate in OpenSSH or RFC4716 format.

Parameters:data (bytes or ASCII string) – The data to import. Returns:An SSHCertificate certificate

read_private_key

asyncssh.read_private_key(filename, passphrase=None)

Read a private key from a file

This function reads a private key from a file. See the function import_private_key() for information about the formats supported.

Parameters:

• filename (str) – The file to read the key from.
• passphrase (str) – (optional) The passphrase to use to decrypt the key.

Returns:

An SSHKey private key

read_public_key

asyncssh.read_public_key(filename)

Read a public key from a file

This function reads a public key from a file. See the function import_public_key() for information about the formats supported.

Parameters:filename (str) – The file to read the key from. Returns:An SSHKey public key

read_certificate

asyncssh.read_certificate(filename)

Read a certificate from a file

This function reads an SSH certificate from a file. See the function import_certificate() for information about the formats supported.

Parameters:filename (str) – The file to read the certificate from. Returns:An SSHCertificate certificate

read_private_key_list

asyncssh.read_private_key_list(filename, passphrase=None)

Read a list of private keys from a file

This function reads a list of private keys from a file. See the function import_private_key() for information about the formats supported. If any of the keys are encrypted, they must all be encrypted with the same passphrase.

Parameters:

• filename (str) – The file to read the keys from.
• passphrase (str) – (optional) The passphrase to use to decrypt the keys.

Returns:

A list of SSHKey private keys

read_public_key_list

asyncssh.read_public_key_list(filename)

Read a list of public keys from a file

This function reads a list of public keys from a file. See the function import_public_key() for information about the formats supported.

Parameters:filename (str) – The file to read the keys from. Returns:A list of SSHKey public keys

read_certificate_list

asyncssh.read_certificate_list(filename)

Read a list of certificates from a file

This function reads a list of SSH certificates from a file. See the function import_certificate() for information about the formats supported.

Parameters:filename (str) – The file to read the certificates from. Returns:A list of SSHCertificate certificates

load_keypairs

asyncssh.load_keypairs(keylist, passphrase=None)

Load SSH private keys and optional matching certificates

This function loads a list of SSH keys and optional matching certificates.

When certificates are specified, the private key is added to the list both with and without the certificate.

Parameters:

• keylist (see Specifying private keys) – The list of private keys and certificates to import.
• passphrase (str) – (optional) The passphrase to use to decrypt private keys.

Returns:

A list of SSHKeyPair objects

load_public_keys

asyncssh.load_public_keys(keylist)

Load public keys

This function loads a list of SSH public keys.

Parameters:keylist (see Specifying public keys) – The list of public keys to import. Returns:A list of SSHKey objects

SSH Agent Support

AsyncSSH supports the ability to use private keys managed by the OpenSSH ssh-agent on UNIX systems. It can connect via a UNIX domain socket to the agent and offload all private key operations to it, avoiding the need to read these keys into AsyncSSH itself. An ssh-agent is automatically used in create_connection() when a valid SSH_AUTH_SOCK is set in the environment. An alternate path to the agent can be specified via the agent_path argument to this function.

An ssh-agent can also be accessed directly from AsyncSSH by calling connect_agent(). When successful, this function returns an SSHAgentClient which can be used to get a list of available keys, add and remove keys, and lock and unlock access to this agent.

SSH agent forwarding may be enabled when making outbound SSH connections by specifying the agent_forwarding argument when calling create_connection(), allowing processes running on the server to tunnel requests back over the SSH connection to the client’s ssh-agent.

Agent forwarding can be enabled when starting an SSH server by specifying the agent_forwarding argument when calling create_server(). In this case, the client’s ssh-agent can be accessed from the server by passing the SSHServerConnection as the argument to connect_agent() instead of a local path. Alternately, when an SSHServerChannel has been opened, the get_agent_path() method may be called on it to get a path to a UNIX domain socket which can be passed as the SSH_AUTH_SOCK to local applications which need this access. Any requests sent to this socket are forwarded over the SSH connection to the client’s ssh-agent.

SSHAgentClient

class asyncssh.SSHAgentClient

SSH agent client

get_keys() Request the available client keys This method is a coroutine which returns a list of client keys available in the ssh-agent. Returns:A list of SSHKeyPair objects
add_keys(keylist=(), passphrase=None, lifetime=None, confirm=False) Add keys to the agent This method adds a list of local private keys and optional matching certificates to the agent. Parameters: keylist (see Specifying private keys) – (optional) The list of keys to add. If not specified, an attempt will be made to load keys from the files .ssh/id_ed25519, .ssh/id_ecdsa, .ssh/id_rsa and .ssh/id_dsa in the user’s home directory with optional matching certificates loaded from the files .ssh/id_ed25519-cert.pub, .ssh/id_ecdsa-cert.pub, .ssh/id_rsa-cert.pub, and .ssh/id_dsa-cert.pub. passphrase (str) – (optional) The passphrase to use to decrypt the keys. lifetime (int or None) – (optional) The time in seconds after which the keys should be automatically deleted, or None to store these keys indefinitely (the default). confirm (bool) – (optional) Whether or not to require confirmation for each private key operation which uses these keys, defaulting to False. Raises: ValueError if the keys cannot be added
add_smartcard_keys(provider, pin=None, lifetime=None, confirm=False) Store keys associated with a smart card in the agent Parameters: provider (str) – The name of the smart card provider pin (str or None) – (optional) The PIN to use to unlock the smart card lifetime (int or None) – (optional) The time in seconds after which the keys should be automatically deleted, or None to store these keys indefinitely (the default). confirm (bool) – (optional) Whether or not to require confirmation for each private key operation which uses these keys, defaulting to False. Raises: ValueError if the keys cannot be added
remove_keys(keylist) Remove a key stored in the agent Parameters:keylist (list of SSHKeyPair) – The list of keys to remove. Raises:ValueError if any keys are not found
remove_smartcard_keys(provider, pin=None) Remove keys associated with a smart card stored in the agent Parameters: provider (str) – The name of the smart card provider pin (str or None) – (optional) The PIN to use to unlock the smart card Raises: ValueError if the keys are not found
remove_all() Remove all keys stored in the agent Raises:ValueError if the keys can’t be removed
lock(passphrase) Lock the agent using the specified passphrase Parameters:passphrase (str) – The passphrase required to later unlock the agent Raises:ValueError if the agent can’t be locked
unlock(passphrase) Unlock the agent using the specified passphrase Parameters:passphrase (str) – The passphrase to use to unlock the agent Raises:ValueError if the agent can’t be unlocked
query_extensions() Return a list of extensions supported by the agent Returns:A list of strings of supported extension names
close() Close the SSH agent connection This method closes the connection to the ssh-agent. Any attempts to use this SSHAgentClient or the key pairs it previously returned will result in an error.

SSHAgentKeyPair

class asyncssh.SSHAgentKeyPair

Surrogate for a key managed by the SSH agent

get_key_type() Return what type of key pair this is This method returns ‘local’ for locally loaded keys, and ‘agent’ for keys managed by an SSH agent.
get_algorithm() Return the algorithm associated with this key pair
get_comment() Return the comment associated with this key pair Returns:str or None
set_comment(comment) Set the comment associated with this key pair Parameters:comment (str or None) – The new comment to associate with this key pair
sign(data) Sign a block of data with this private key
remove() Remove this key pair from the agent

connect_agent

asyncssh.connect_agent(agent_path=None, *, loop=None)

Make a connection to the SSH agent

This function attempts to connect to an ssh-agent process listening on a UNIX domain socket at agent_path. If not provided, it will attempt to get the path from the SSH_AUTH_SOCK environment variable.

If the connection is successful, an SSHAgentClient object is returned that has methods on it you can use to query the ssh-agent. If no path is specified and the environment variable is not set or the connection to the agent fails, this function returns None.

Parameters:

• agent_path (str or SSHServerConnection) – (optional) The path to use to contact the ssh-agent process, or the SSHServerConnection to forward the agent request over.
• loop – (optional) The event loop to use when creating the connection. If not specified, the default event loop is used.

Returns:

An SSHAgentClient or None

Known Hosts

AsyncSSH supports OpenSSH-style known_hosts files, including both plain and hashed host entries. Regular and negated host patterns are supported in plain entries. AsyncSSH also supports the @cert_authority marker to indicate certificate authority keys and the @revoked marker to indicate revoked keys which should no longer be trusted.

Specifying known hosts

Known hosts may be passed into AsyncSSH via the known_hosts argument to create_connection(). This can be the name of a file containing a list of known hosts or an SSHKnownHosts object which was previously imported from a string by calling import_known_hosts() or read from a file by calling read_known_hosts().

Alternately, known hosts can be passed into AsyncSSH as a sequence of three public key lists containing trusted host keys, trusted CA keys, and revoked keys which should no longer be trusted. See Specifying public keys for the allowed form of each of these values.

SSHKnownHosts

class asyncssh.SSHKnownHosts

An SSH known hosts list

match(host, addr, port) Match a host, IP address, and port against known_hosts patterns If the port is not the default port and no match is found for it, the lookup is attempted again without a port number. Parameters: host (str) – The hostname of the target host addr (str) – The IP address of the target host port (int) – The port number on the target host, or None for the default Returns: A tuple of matching host keys, CA keys, and revoked keys

import_known_hosts

asyncssh.import_known_hosts(data)

Import SSH known hosts

This function imports known host patterns and keys in OpenSSH known hosts format.

Parameters:data (str) – The known hosts data to import Returns:An SSHKnownHosts object

read_known_hosts

asyncssh.read_known_hosts(filename)

Read SSH known hosts from a file

This function reads known host patterns and keys in OpenSSH known hosts format from a file.

Parameters:filename (str) – The file to read the known hosts from Returns:An SSHKnownHosts object

match_known_hosts

asyncssh.match_known_hosts(known_hosts, host, addr, port)

Match a host, IP address, and port against a known_hosts list

This function looks up a host, IP address, and port in a list of host patterns in OpenSSH known_hosts format and returns the host keys, CA keys, and revoked keys which match.

The known_hosts argument can be a string containing the filename to load the host patterns from, a byte string containing host pattern data, or an already loaded SSHKnownHosts object.

If the port is not the default port and no match is found for it, the lookup is attempted again without a port number.

Parameters:

• known_hosts (str or bytes or SSHKnownHosts) – The host patterns to match against
• host (str) – The hostname of the target host
• addr (str) – The IP address of the target host
• port (int) – The port number on the target host, or None for the default

Returns:

A tuple of matching host keys, CA keys, and revoked keys

Authorized Keys

AsyncSSH supports OpenSSH-style authorized_keys files, including the cert-authority option to validate user certificates, enforcement of from and principals options to restrict key matching, enforcement of no-X11-forwarding, no-agent-forwarding, no-pty, no-port-forwarding, and permitopen options, and support for command and environment options.

Specifying authorized keys

Authorized keys may be passed into AsyncSSH via the authorized_client_keys argument to create_server() or by calling set_authorized_keys() on the SSHServerConnection from within the begin_auth() method in SSHServer.

Authorized keys can be provided as either the name of a file to read the keys from or an SSHAuthorizedKeys object which was previously imported from a string by calling import_authorized_keys() or read from a file by calling read_authorized_keys().

SSHAuthorizedKeys

class asyncssh.SSHAuthorizedKeys

An SSH authorized keys list

import_authorized_keys

asyncssh.import_authorized_keys(data)

Import SSH authorized keys

This function imports public keys and associated options in OpenSSH authorized keys format.

Parameters:data (str) – The key data to import. Returns:An SSHAuthorizedKeys object

read_authorized_keys

asyncssh.read_authorized_keys(filename)

Read SSH authorized keys from a file

This function reads public keys and associated options in OpenSSH authorized_keys format from a file.

Parameters:filename (str) – The file to read the keys from. Returns:An SSHAuthorizedKeys object

Exceptions

PasswordChangeRequired

exception asyncssh.PasswordChangeRequired(prompt, lang='en-US')

SSH password change required

This exception is raised during password validation on the server to indicate that a password change is required. It shouuld be raised when the password provided is valid but expired, to trigger the client to provide a new password.

Parameters:

• prompt (str) – The prompt requesting that the user enter a new password
• lang (str) – The language that the prompt is in

BreakReceived

exception asyncssh.BreakReceived(msec)

SSH break request received

This exception is raised on an SSH server stdin stream when the client sends a break on the channel.

Parameters:msec (int) – The duration of the break in milliseconds

SignalReceived

exception asyncssh.SignalReceived(signal)

SSH signal request received

This exception is raised on an SSH server stdin stream when the client sends a signal on the channel.

Parameters:signal (str) – The name of the signal sent by the client

TerminalSizeChanged

exception asyncssh.TerminalSizeChanged(width, height, pixwidth, pixheight)

SSH terminal size change notification received

This exception is raised on an SSH server stdin stream when the client sends a terminal size change on the channel.

Parameters:

• width (int) – The new terminal width
• height (int) – The new terminal height
• pixwidth (int) – The new terminal width in pixels
• pixheight (int) – The new terminal height in pixels

DisconnectError

exception asyncssh.DisconnectError(code, reason, lang='en-US')

SSH disconnect error

This exception is raised when a serious error occurs which causes the SSH connection to be disconnected. Exception codes should be taken from disconnect reason codes.

Parameters:

• code (int) – Disconnect reason, taken from disconnect reason codes
• reason (str) – A human-readable reason for the disconnect
• lang (str) – The language the reason is in

ChannelOpenError

exception asyncssh.ChannelOpenError(code, reason, lang='en-US')

SSH channel open error

This exception is raised by connection handlers to report channel open failures.

Parameters:

• code (int) – Channel open failure reason, taken from channel open failure reason codes
• reason (str) – A human-readable reason for the channel open failure
• lang (str) – The language the reason is in

ProcessError

exception asyncssh.ProcessError(exit_status, exit_signal)

SSH Process error

This exception is raised when an SSHClientProcess exits with a non-zero exit status and error checking is enabled. In addition to the usual error code, reason, and language, it contains the following fields:

Field	Description	Type
exit_status	The exit status returned, or -1 if an exit signal is sent	int
exit_signal	The exit signal sent (if any) in the form of a tuple containing the signal name, a bool for whether a core dump occurred, a message associated with the signal, and the language the message was in	tuple or None

SFTPError

exception asyncssh.SFTPError(code, reason, lang='en-US')

SFTP error

This exception is raised when an error occurs while processing an SFTP request. Exception codes should be taken from SFTP error codes.

Parameters:

• code (int) – Disconnect reason, taken from disconnect reason codes
• reason (str) – A human-readable reason for the disconnect
• lang (str) – The language the reason is in

KeyImportError

exception asyncssh.KeyImportError

Key import error

This exception is raised by key import functions when the data provided cannot be imported as a valid key.

KeyExportError

exception asyncssh.KeyExportError

Key export error

This exception is raised by key export functions when the requested format is unknown or encryption is requested for a format which doesn’t support it.

KeyEncryptionError

exception asyncssh.KeyEncryptionError

Key encryption error

This exception is raised by key decryption functions when the data provided is not a valid encrypted private key.

KeyGenerationError

exception asyncssh.KeyGenerationError

Key generation error

This exception is raised by generate_private_key(), generate_user_certificate() or generate_host_certificate() when the requested parameters are unsupported.

Supported Algorithms

Key exchange algorithms

The following are the key exchange algorithms currently supported by AsyncSSH:

curve25519-sha256

curve25519-sha256@libssh.org

ecdh-sha2-nistp521

ecdh-sha2-nistp384

ecdh-sha2-nistp256

diffie-hellman-group-exchange-sha256

diffie-hellman-group16-sha512

diffie-hellman-group18-sha512

diffie-hellman-group14-sha256

diffie-hellman-group-exchange-sha1

diffie-hellman-group14-sha1

diffie-hellman-group1-sha1

Curve25519 support is only available when the libnacl package and libsodium library are installed.

Encryption algorithms

The following are the encryption algorithms currently supported by AsyncSSH:

chacha20-poly1305@openssh.com

aes256-ctr

aes192-ctr

aes128-ctr

aes256-gcm@openssh.com

aes128-gcm@openssh.com

aes256-cbc

aes192-cbc

aes128-cbc

3des-cbc

blowfish-cbc

cast128-cbc

arcfour256

arcfour128

arcfour

Chacha20-poly1305 support is only available when the libnacl package and libsodium library are installed.

MAC algorithms

The following are the MAC algorithms currently supported by AsyncSSH:

umac-64-etm@openssh.com

umac-128-etm@openssh.com

hmac-sha2-256-etm@openssh.com

hmac-sha2-512-etm@openssh.com

hmac-sha1-etm@openssh.com

hmac-md5-etm@openssh.com

hmac-sha2-256-96-etm@openssh.com

hmac-sha2-512-96-etm@openssh.com

hmac-sha1-96-etm@openssh.com

hmac-md5-96-etm@openssh.com

umac-64@openssh.com

umac-128@openssh.com

hmac-sha2-256

hmac-sha2-512

hmac-sha1

hmac-md5

hmac-sha2-256-96

hmac-sha2-512-96

hmac-sha1-96

hmac-md5-96

UMAC support is only available when the nettle library is installed.

Compression algorithms

The following are the compression algorithms currently supported by AsyncSSH:

zlib@openssh.com

zlib

none

Signature algorithms

The following are the public key signature algorithms currently supported by AsyncSSH:

ssh-ed25519

ecdsa-sha2-nistp521

ecdsa-sha2-nistp384

ecdsa-sha2-nistp256

rsa-sha2-256

rsa-sha2-512

ssh-rsa

ssh-dss

Public key & certificate algorithms

The following are the public key and certificate algorithms currently supported by AsyncSSH:

ssh-ed25519-cert-v01@openssh.com

ecdsa-sha2-nistp521-cert-v01@openssh.com

ecdsa-sha2-nistp384-cert-v01@openssh.com

ecdsa-sha2-nistp256-cert-v01@openssh.com

ssh-rsa-cert-v01@openssh.com

ssh-dss-cert-v01@openssh.com

ssh-ed25519

ecdsa-sha2-nistp521

ecdsa-sha2-nistp384

ecdsa-sha2-nistp256

rsa-sha2-256

rsa-sha2-512

ssh-rsa

ssh-dss

Ed25519 support is only available when the libnacl package and libsodium library are installed.

Constants

Certificate types

The following values can be specified as certificate types:

CERT_TYPE_USER

CERT_TYPE_HOST

Disconnect reasons

The following values defined in section 11.1 of RFC 4253#section-11.1 can be specified as disconnect reason codes:

DISC_HOST_NOT_ALLOWED_TO_CONNECT

DISC_PROTOCOL_ERROR

DISC_KEY_EXCHANGE_FAILED

DISC_RESERVED

DISC_MAC_ERROR

DISC_COMPRESSION_ERROR

DISC_SERVICE_NOT_AVAILABLE

DISC_PROTOCOL_VERSION_NOT_SUPPORTED

DISC_HOST_KEY_NOT_VERIFYABLE

DISC_CONNECTION_LOST

DISC_BY_APPLICATION

DISC_TOO_MANY_CONNECTIONS

DISC_AUTH_CANCELLED_BY_USER

DISC_NO_MORE_AUTH_METHODS_AVAILABLE

DISC_ILLEGAL_USER_NAME

Channel open failure reasons

The following values defined in section 5.1 of RFC 4254#section-5.1 can be specified as channel open failure reason codes:

OPEN_ADMINISTRATIVELY_PROHIBITED

OPEN_CONNECT_FAILED

OPEN_UNKNOWN_CHANNEL_TYPE

OPEN_RESOURCE_SHORTAGE

In addition, AsyncSSH defines the following channel open failure reason codes:

OPEN_REQUEST_X11_FORWARDING_FAILED

OPEN_REQUEST_PTY_FAILED

OPEN_REQUEST_SESSION_FAILED

SFTP error codes

The following values defined in the SSH File Transfer Internet Draft can be specified as SFTP error codes:

FX_OK

FX_EOF

FX_NO_SUCH_FILE

FX_PERMISSION_DENIED

FX_FAILURE

FX_BAD_MESSAGE

FX_NO_CONNECTION

FX_CONNECTION_LOST

FX_OP_UNSUPPORTED

Extended data types

The following values defined in section 5.2 of RFC 4254#section-5.2 can be specified as SSH extended channel data types:

EXTENDED_DATA_STDERR

POSIX terminal modes

The following values defined in section 8 of RFC 4254#section-8 can be specified as PTY mode opcodes:

PTY_OP_END

PTY_VINTR

PTY_VQUIT

PTY_VERASE

PTY_VKILL

PTY_VEOF

PTY_VEOL

PTY_VEOL2

PTY_VSTART

PTY_VSTOP

PTY_VSUSP

PTY_VDSUSP

PTY_VREPRINT

PTY_WERASE

PTY_VLNEXT

PTY_VFLUSH

PTY_VSWTCH

PTY_VSTATUS

PTY_VDISCARD

PTY_IGNPAR

PTY_PARMRK

PTY_INPCK

PTY_ISTRIP

PTY_INLCR

PTY_IGNCR

PTY_ICRNL

PTY_IUCLC

PTY_IXON

PTY_IXANY

PTY_IXOFF

PTY_IMAXBEL

PTY_ISIG

PTY_ICANON

PTY_XCASE

PTY_ECHO

PTY_ECHOE

PTY_ECHOK

PTY_ECHONL

PTY_NOFLSH

PTY_TOSTOP

PTY_IEXTEN

PTY_ECHOCTL

PTY_ECHOKE

PTY_PENDIN

PTY_OPOST

PTY_OLCUC

PTY_ONLCR

PTY_OCRNL

PTY_ONOCR

PTY_ONLRET

PTY_CS7

PTY_CS8

PTY_PARENB

PTY_PARODD

PTY_OP_ISPEED

PTY_OP_OSPEED