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

Question

I want to run a tail -f logfile command on a remote machine using python\'s paramiko module. I\'ve been attempting it so far in the following fashion:

Answer 1

The way I've solved this is with a context manager. This will make sure my long running commands are aborted. The key logic is to wrap to mimic SSHClient.exec_command but capture the created channel and use a Timer that will close that channel if the command runs for too long.

import paramiko
import threading


class TimeoutChannel:

    def __init__(self, client: paramiko.SSHClient, timeout):
        self.expired = False
        self._channel: paramiko.channel = None
        self.client = client
        self.timeout = timeout

    def __enter__(self):
        self.timer = threading.Timer(self.timeout, self.kill_client)
        self.timer.start()

        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        print("Exited Timeout. Timed out:", self.expired)
        self.timer.cancel()

        if exc_val:
            return False  # Make sure the exceptions are re-raised

        if self.expired:
            raise TimeoutError("Command timed out")

    def kill_client(self):
        self.expired = True
        print("Should kill client")
        if self._channel:
            print("We have a channel")
            self._channel.close()

    def exec(self, command, bufsize=-1, timeout=None, get_pty=False, environment=None):
        self._channel = self.client.get_transport().open_session(timeout=timeout)
        if get_pty:
            self._channel.get_pty()
        self._channel.settimeout(timeout)
        if environment:
            self._channel.update_environment(environment)
        self._channel.exec_command(command)
        stdin = self._channel.makefile_stdin("wb", bufsize)
        stdout = self._channel.makefile("r", bufsize)
        stderr = self._channel.makefile_stderr("r", bufsize)
        return stdin, stdout, stderr

To use the code it's pretty simple now, the first example will throw a TimeoutError

ssh = paramiko.SSHClient()
ssh.connect('hostname', username='user', password='pass')

with TimeoutChannel(ssh, 3) as c:
    ssh_stdin, ssh_stdout, ssh_stderr = c.exec("cat")    # non-blocking
    exit_status = ssh_stdout.channel.recv_exit_status()  # block til done, will never complete because cat wants input

This code will work fine (unless the host is under insane load!)

ssh = paramiko.SSHClient()
ssh.connect('hostname', username='user', password='pass')

with TimeoutChannel(ssh, 3) as c:
    ssh_stdin, ssh_stdout, ssh_stderr = c.exec("uptime")    # non-blocking
    exit_status = ssh_stdout.channel.recv_exit_status()     # block til done, will complete quickly
    print(ssh_stdout.read().decode("utf8"))                 # Show results