Paramiko and exec_command - killing remote process?

Question

I'm using Paramiko to tail -f a file on a remote server.

Previously, we were running this via ssh -t, but that proved flaky, and the -t caused issues with our remote scheduling system.

My question is how to kill tail when the script catches a SIGINT?

My script (based on Long-running ssh commands in python paramiko module (and how to end them))

#!/usr/bin/env python2
import paramiko
import select

client = paramiko.SSHClient()
client.load_system_host_keys()
client.connect('someserver', username='victorhooi', password='blahblah')
transport = client.get_transport()
channel = transport.open_session()

channel.exec_command("tail -f /home/victorhooi/macbeth.txt")
while True:
    try:
        rl, wl, xl = select.select([channel],[],[],0.0)
        if len(rl) > 0:
            # Must be stdout
            print channel.recv(1024)
    except KeyboardInterrupt:
        print("Caught control-C")
        client.close()
        channel.close()
        exit(0)

The script catches my Ctrl-C successfully, and ends. However, it leaves the tail -f process running on the remote system,.

Neither client.close() nor channel.close() seem to terminate it.

What command can I issue in the except block to kill it?

The remote server is running Solaris 10.

Answer 1

You should use ssh keepalives... the problem you have is that the remote shell has no way of knowing (by default) that your ssh session was killed. Keepalives will enable the remote shell to detect that you killed the session

client = paramiko.SSHClient()
client.load_system_host_keys()
client.connect('someserver', username='victorhooi', password='blahblah')
transport = client.get_transport()
transport.set_keepalive(1)   # <------------------------------
# ... carry on as usual...

Set the keepalive value as low as you like (even 1 second)... after several seconds, the remote shell will see that the ssh login died, and it will terminate any processes that were spawned by it.

Answer 2

There is one way to do this. It works like on the shell

ssh -t commandname

The option -t is opening a pseudo pty to help ssh to track how long this process should last. the same can be done via pormiko via

channel.get_pty()

prior to execute_command(...). This will not open a shell like it does with channel.invoke_shell(), it just requests such a pseudo interface to tie all processes to. The effect can also be seen if ps aux is issued on the remote machine, the process is now attached to the sshd with a ptxXY interface.