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Editorial Team
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Asked: 2026-05-26T06:26:22+00:00

I have a service that spawns threads. The threads are started by providing a

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I have a service that spawns threads.
The threads are started by providing a target function.
It would appear that the thread doesn’t “die” when the function ends. I know this because the thread makes some SSH connections with Paramiko (via Fabric), and if I do an lsof I see the SSH connections are still active after the function completes.
How can I make sure that a thread dies when its target function completes?

Here is an example of what I am working with:

from time import sleep
from threading import Thread
from fabric.api import run, settings

def thread_func(host):
    with settings(host_string=host):
        run('ls -lht /tmp')

def spawn_thread(host):
    t = Thread(
        target=thread_func,
        args=(host,)
    )
    t.start()

spawn_thread('node1.example.com')
while True:
    sleep(1)

And if I run sudo lsof | grep ssh in another terminal while the above code is in its infinite loop I’ll see the following, even after I know that the thread should not exist anymore:

python    6924      daharon    3u     IPv4             170520        0t0        TCP 10.1.1.173:47368->node1.example.com:ssh (ESTABLISHED)
python    6924      daharon    5u     IPv4             170524        0t0        TCP 10.1.1.173:47369->node1.example.com:ssh (ESTABLISHED)
python    6924 6930 daharon    3u     IPv4             170520        0t0        TCP 10.1.1.173:47368->node1.example.com:ssh (ESTABLISHED)
python    6924 6930 daharon    5u     IPv4             170524        0t0        TCP 10.1.1.173:47369->node1.example.com:ssh (ESTABLISHED)
python    6924 6932 daharon    3u     IPv4             170520        0t0        TCP 10.1.1.173:47368->node1.example.com:ssh (ESTABLISHED)
python    6924 6932 daharon    5u     IPv4             170524        0t0        TCP 10.1.1.173:47369->node1.example.com:ssh (ESTABLISHED)
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1 Answer

  1. Editorial Team

    Are you sure your fabric module is doing the ssh only for the duration of the ls command. That is, it should be doing the equivalent of

    ssh host ls -lht /tmp

    This commandline will open a remote shell to run the ls -lht command and then shutdown.

    But I suspect the Fabric library might be doing the equivalent of:

    ssh host

    host$ ls -lht /tmp
    .
    .

    Of course it’s not providing a real tty but there are different ssh options that allow keeping a connection open without an interactive tty. This would be desirable in certain cases (e.g., if you run lots of commands on the same host, this technique will reuse the existing ssh session instead of opening new session every time. Check the documentation for arguments to enable or disable such session caching.

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