test/pexpect-2.4/examples/ssh_tunnel.py

#!/usr/bin/env python

"""This starts an SSH tunnel to a given host. If the SSH process ever dies then
this script will detect that and restart it. I use this under Cygwin to keep
open encrypted tunnels to port 25 (SMTP), port 143 (IMAP4), and port 110
(POP3). I set my mail client to talk to localhost and I keep this script
running in the background.

Note that this is a rather stupid script at the moment because it just looks to
see if any ssh process is running. It should really make sure that our specific
ssh process is running. The problem is that ssh is missing a very useful
feature. It has no way to report the process id of the background daemon that
it creates with the -f command. This would be a really useful script if I could
figure a way around this problem. """

import pexpect
import getpass
import time

# SMTP:25 IMAP4:143 POP3:110
tunnel_command = 'ssh -C -N -f -L 25:127.0.0.1:25 -L 143:127.0.0.1:143 -L 110:127.0.0.1:110 %(user)@%(host)'
host = raw_input('Hostname: ')
user = raw_input('Username: ')
X = getpass.getpass('Password: ')

def get_process_info ():

    # This seems to work on both Linux and BSD, but should otherwise be considered highly UNportable.

    ps = pexpect.run ('ps ax -O ppid')
    pass
def start_tunnel ():
    try:
        ssh_tunnel = pexpect.spawn (tunnel_command % globals())
        ssh_tunnel.expect ('password:')
        time.sleep (0.1)
        ssh_tunnel.sendline (X)
        time.sleep (60) # Cygwin is slow to update process status.
        ssh_tunnel.expect (pexpect.EOF)

    except Exception, e:
        print str(e)

def main ():

    while True:
        ps = pexpect.spawn ('ps')
        time.sleep (1)
        index = ps.expect (['/usr/bin/ssh', pexpect.EOF, pexpect.TIMEOUT])
        if index == 2:
            print 'TIMEOUT in ps command...'
            print str(ps)
            time.sleep (13)
        if index == 1:
            print time.asctime(),
            print 'restarting tunnel'
            start_tunnel ()
            time.sleep (11)
	        print 'tunnel OK'
        else:
            # print 'tunnel OK'
            time.sleep (7)

if __name__ == '__main__':
    main ()

# This was for older SSH versions that didn't have -f option
#tunnel_command = 'ssh -C -n -L 25:%(host)s:25 -L 110:%(host)s:110 %(user)s@%(host)s -f nothing.sh'
#nothing_script = """#!/bin/sh
#while true; do sleep 53; done
#"""