def exec_command(self, command, bufsize=-<NUM_LIT:1>):
chan = self._transport.open_session()<EOL>chan.exec_command(command)<EOL>stdin = chan.makefile('<STR_LIT:wb>', bufsize)<EOL>stdout = chan.makefile('<STR_LIT:rb>', bufsize)<EOL>stderr = chan.makefile_stderr('<STR_LIT:rb>', bufsize)<EOL>return stdin, stdout, stderr<EOL>
Execute a command on the SSH server.  A new L{Channel} is opened and
the requested command is executed.  The command's input and output
streams are returned as python C{file}-like objects representing
stdin, stdout, and stderr.

@param command: the command to execute
@type command: str
@param bufsize: interpreted the same way as by the built-in C{file()} function in python
@type bufsize: int
@return: the stdin, stdout, and stderr of the executing command
@rtype: tuple(L{ChannelFile}, L{ChannelFile}, L{ChannelFile})

@raise SSHException: if the server fails to execute the command