Package org.apache.commons.net.bsd

Class RExecClient

  • Direct Known Subclasses:
    RCommandClient
    public class RExecClient
extends SocketClient
    RExecClient implements the rexec() facility that first appeared in 4.2BSD Unix. This class will probably only be of use for connecting to Unix systems and only when the rexecd daemon is configured to run, which is a rarity these days because of the security risks involved. However, rexec() can be very useful for performing administrative tasks on a network behind a firewall.

    As with virtually all of the client classes in org.apache.commons.net, this class derives from SocketClient, inheriting its connection methods. The way to use RExecClient is to first connect to the server, call the rexec() 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 rexecd 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 rexec() to true . The standard input of the remote process can be written to through the output stream returned by getOutputSream().

    See Also:
    SocketClient, RCommandClient, RLoginClient

    • Field Detail

      • DEFAULT_PORT

        public static final int DEFAULT_PORT
        The default rexec port. Set to 512 in BSD Unix.
        See Also:
        Constant Field Values

      • _errorStream_

        protected java.io.InputStream _errorStream_
        If a separate error stream is requested, _errorStream_ will point to an InputStream from which the standard error of the remote process can be read (after a call to rexec()). Otherwise, _errorStream_ will be null.

    • Constructor Detail

      • RExecClient

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

    • Method Detail

      • getInputStream

        public java.io.InputStream getInputStream()
        Returns the InputStream from which the standard output of the remote process can be read. The input stream will only be set after a successful rexec() invocation.
        Returns:
        The InputStream from which the standard output of the remote process can be read.

      • getOutputStream

        public java.io.OutputStream getOutputStream()
        Returns the OutputStream through which the standard input of the remote process can be written. The output stream will only be set after a successful rexec() invocation.
        Returns:
        The OutputStream through which the standard input of the remote process can be written.

      • getErrorStream

        public java.io.InputStream getErrorStream()
        Returns the InputStream from which the standard error of the remote process can be read if a separate error stream is requested from the server. Otherwise, null will be returned. The error stream will only be set after a successful rexec() invocation.
        Returns:
        The InputStream from which the standard error of the remote process can be read if a separate error stream is requested from the server. Otherwise, null will be returned.

      • rexec

        public void rexec​(java.lang.String username,
                  java.lang.String password,
                  java.lang.String command,
                  boolean separateErrorStream)
           throws java.io.IOException
        Remotely executes a command through the rexecd daemon on the server to which the RExecClient is connected. After calling this method, you may interact with the remote process through its standard input, output, and error streams. You will typically be able to detect the termination of the remote process after reaching end of file on its standard output (accessible through getInputStream() . Disconnecting from the server or closing the process streams before reaching end of file will not necessarily terminate the remote process.

        If a separate error stream is requested, the remote server will connect to a local socket opened by RExecClient, providing an independent stream through which standard error will be transmitted. RExecClient will do a simple security check when it accepts a connection for this error stream. If the connection does not originate from the remote server, an IOException will be thrown. This serves as a simple protection against possible hijacking of the error stream by an attacker monitoring the rexec() negotiation. You may disable this behavior with setRemoteVerificationEnabled() .

        Parameters:
        username - The account name on the server through which to execute the command.
        password - The plain text password of the user account.
        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.
        Throws:
        java.io.IOException - If the rexec() attempt fails. The exception will contain a message indicating the nature of the failure.

      • rexec

        public void rexec​(java.lang.String username,
                  java.lang.String password,
                  java.lang.String command)
           throws java.io.IOException
        Same as rexec(username, password, command, false);
        Parameters:
        username - the user name
        password - the password
        command - the command to run
        Throws:
        java.io.IOException - if an error occurs

      • disconnect

        public void disconnect()
                throws java.io.IOException
        Disconnects from the server, closing all associated open sockets and streams.
        Overrides:
        disconnect in class SocketClient
        Throws:
        java.io.IOException - If there an error occurs while disconnecting.

      • setRemoteVerificationEnabled

        public final void setRemoteVerificationEnabled​(boolean enable)
        Enable or disable verification that the remote host connecting to create a separate error stream is the same as the host to which the standard out stream is connected. The default is for verification to be enabled. You may set this value at any time, whether the client is currently connected or not.
        Parameters:
        enable - True to enable verification, false to disable verification.

      • isRemoteVerificationEnabled

        public final boolean isRemoteVerificationEnabled()
        Return whether or not verification of the remote host providing a separate error stream is enabled. The default behavior is for verification to be enabled.
        Returns:
        True if verification is enabled, false if not.