org.apache.commons.net.bsd

Class RCommandClient

Known Direct Subclasses:
RLoginClient

public class RCommandClient
extends RExecClient

RCommandClient is very similar to RExecClient, from which it is derived, and implements the rcmd() facility that first appeared in 4.2BSD Unix. rcmd() is the facility used by the rsh (rshell) and other commands to execute a command on another machine from a trusted host without issuing a password. The trust relationship between two machines is established by the contents of a machine's /etc/hosts.equiv file and a user's .rhosts file. These files specify from which hosts and accounts on those hosts rcmd() requests will be accepted. The only additional measure for establishing trust is that all client connections must originate from a port between 512 and 1023. Consequently, there is an upper limit to the number of rcmd connections that can be running simultaneously. The required ports are reserved ports on Unix systems, and can only be bound by a process running with root permissions (to accomplish this rsh, rlogin, and related commands usualy have the suid bit set). Therefore, on a Unix system, you will only be able to successfully use the RCommandClient class if the process runs as root. However, there is no such restriction on Windows95 and some other systems. The security risks are obvious. However, when carefully used, rcmd() can be very useful when used behind a firewall.

As with virtually all of the client classes in org.apache.commons.net, this class derives from SocketClient. But it overrides most of its connection methods so that the local Socket will originate from an acceptable rshell port. The way to use RCommandClient is to first connect to the server, call the rcommand() method, and then fetch the connection's input, output, and optionally error streams. Interaction with the remote command is controlled entirely through the I/O streams. Once you have finished processing the streams, you should invoke disconnect() to clean up properly.

By default the standard output and standard error streams of the remote process are transmitted over the same connection, readable from the input stream returned by getInputStream() . However, it is possible to tell the rshd daemon to return the standard error stream over a separate connection, readable from the input stream returned by getErrorStream() . You can specify that a separate connection should be created for standard error by setting the boolean separateErrorStream parameter of rcommand() to true . The standard input of the remote process can be written to through the output stream returned by getOutputStream() .

See Also:
SocketClient, RExecClient, RLoginClient

Field Summary

static int
DEFAULT_PORT
The default rshell port.
static int
MAX_CLIENT_PORT
The largest port number an rcmd client may use.
static int
MIN_CLIENT_PORT
The smallest port number an rcmd client may use.

Fields inherited from class org.apache.commons.net.bsd.RExecClient

DEFAULT_PORT, _errorStream_

Fields inherited from class org.apache.commons.net.SocketClient

NETASCII_EOL, _defaultPort_, _input_, _isConnected_, _output_, _socketFactory_, _socket_, _timeout_

Constructor Summary

RCommandClient()
The default RCommandClient constructor.

Method Summary

void
connect(InetAddress host, int port)
Opens a Socket connected to a remote host at the specified port and originating from the current host at a port in a range acceptable to the BSD rshell daemon.
void
connect(InetAddress host, int port, InetAddress localAddr)
Opens a Socket connected to a remote host at the specified port and originating from the specified local address using a port in a range acceptable to the BSD rshell daemon.
void
connect(InetAddress host, int port, InetAddress localAddr, int localPort)
Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port.
void
connect(String hostname, int port)
Opens a Socket connected to a remote host at the specified port and originating from the current host at a port in a range acceptable to the BSD rshell daemon.
void
connect(String hostname, int port, InetAddress localAddr)
Opens a Socket connected to a remote host at the specified port and originating from the specified local address using a port in a range acceptable to the BSD rshell daemon.
void
connect(String hostname, int port, InetAddress localAddr, int localPort)
Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port.
void
rcommand(String localUsername, String remoteUsername, String command)
Same as rcommand(localUsername, remoteUsername, command, false);
void
rcommand(String localUsername, String remoteUsername, String command, boolean separateErrorStream)
Remotely executes a command through the rshd daemon on the server to which the RCommandClient is connected.

Methods inherited from class org.apache.commons.net.bsd.RExecClient

disconnect, getErrorStream, getInputStream, getOutputStream, isRemoteVerificationEnabled, rexec, rexec, setRemoteVerificationEnabled

Methods inherited from class org.apache.commons.net.SocketClient

_connectAction_, connect, connect, connect, connect, connect, connect, disconnect, getDefaultPort, getDefaultTimeout, getLocalAddress, getLocalPort, getRemoteAddress, getRemotePort, getSoLinger, getSoTimeout, getTcpNoDelay, isConnected, setDefaultPort, setDefaultTimeout, setSoLinger, setSoTimeout, setSocketFactory, setTcpNoDelay, verifyRemote

Field Details

DEFAULT_PORT

public static final int DEFAULT_PORT
The default rshell port. Set to 514 in BSD Unix.

Field Value:
514


MAX_CLIENT_PORT

public static final int MAX_CLIENT_PORT
The largest port number an rcmd client may use. By BSD convention this number is 1023.

Field Value:
1023


MIN_CLIENT_PORT

public static final int MIN_CLIENT_PORT
The smallest port number an rcmd client may use. By BSD convention this number is 512.

Field Value:
512

Constructor Details

RCommandClient

public RCommandClient()
The default RCommandClient constructor. Initializes the default port to DEFAULT_PORT .

Method Details

connect

public void connect(InetAddress host,
                    int port)
            throws SocketException,
                   IOException
Overrides:
connect in interface SocketClient

Parameters:
host - The remote host.
port - The port to connect to on the remote host.


connect

public void connect(InetAddress host,
                    int port,
                    InetAddress localAddr)
            throws SocketException,
                   BindException,
                   IOException

Parameters:
host - The remote host.
port - The port to connect to on the remote host.
localAddr - The local address to use.


connect

public void connect(InetAddress host,
                    int port,
                    InetAddress localAddr,
                    int localPort)
            throws SocketException,
                   IOException,
                   IllegalArgumentException
Overrides:
connect in interface SocketClient

Parameters:
host - The remote host.
port - The port to connect to on the remote host.
localAddr - The local address to use.
localPort - The local port to use.


connect

public void connect(String hostname,
                    int port)
            throws SocketException,
                   IOException
Overrides:
connect in interface SocketClient

Parameters:
hostname - The name of the remote host.
port - The port to connect to on the remote host.


connect

public void connect(String hostname,
                    int port,
                    InetAddress localAddr)
            throws SocketException,
                   IOException

Parameters:
hostname - The remote host.
port - The port to connect to on the remote host.
localAddr - The local address to use.


connect

public void connect(String hostname,
                    int port,
                    InetAddress localAddr,
                    int localPort)
            throws SocketException,
                   IOException,
                   IllegalArgumentException
Overrides:
connect in interface SocketClient

Parameters:
hostname - The name of the remote host.
port - The port to connect to on the remote host.
localAddr - The local address to use.
localPort - The local port to use.


rcommand

public void rcommand(String localUsername,
                     String remoteUsername,
                     String command)
            throws IOException
Same as rcommand(localUsername, remoteUsername, command, false);


rcommand

public void rcommand(String localUsername,
                     String remoteUsername,
                     String command,
                     boolean separateErrorStream)
            throws IOException

Parameters:
localUsername - The user account on the local machine that is requesting the command execution.
remoteUsername - The account name on the server through which to execute the command.
command - The command, including any arguments, to execute.
separateErrorStream - True if you would like the standard error to be transmitted through a different stream than standard output. False if not.