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

While not the most efficient method, this should work. After you CTRL+C; In the KeyboardInterrupt handler you could exec_command("killall -u %s tail" % uname) like so:

#!/usr/bin/env python2

import paramiko
import select

import time
ltime = time.time()

# Or use random:
# import random
# ltime = random.randint(0, 500)

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

channel.exec_command("tail -%df /home/victorhooi/macbeth.txt" % ltime)
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")
        channel.close()
        try:
            # open new socket and kill the proc..
            client.get_transport().open_session().exec_command("kill -9 `ps -fu %s | grep 'tail -%df /home/victorhooi/macbeth.txt' | grep -v grep | awk '{print $2}'`" % (uname, ltime))
        except:
            pass
    
        client.close()
        exit(0)

This would kill any open processes named tail. That may cause issues though if you have tails open that you dont want to close, if thats the case you could grep a ps, get the pid and kill -9 it.

First, set tail to read n lines from end of file before following. set n to a unique nuber like time.time(), since tail doesn’t care if that number is larger then the number of lines in the file, the large number from time.time()shouldnt cause issues and will be unique. Then grep for that unique number in the ps:

   client.get_transport().open_session().exec_command("kill -9 `ps -fu %s | grep 'tail -%df /home/victorhooi/macbeth.txt' | grep -v grep | awk '{print $2}'`" % (uname, ltime))