How to end/kill all incoming SSH connections?

Question

I am developing a some code in order to communicate between a PC and a Raspberry Pi via SSH. When the PC opens a SSH connection to the RPi a window with a short message pops up on the RPi's screen. When there are no open SSH connections said window closes itself. Everything works just fine so far.

Now, I want to add a button in said window on the RPi in order to terminate all SSH incoming connections. Is there a Unix command for that? A Python module or method that does that would be fine as well, since the RPi's code is written in Python.

According to my research terminating a SSH connection can be done by killing the corresponding process via its PID. Since I want to kill all SSH processes/connections autonomously I am looking for an easier solution.

Thanks for your help!

(The Raspberry Pi runs on Raspbian 8 (jessie))

Answer 1

Killing all the SSH server processes isn't hard if you have pkill/pgrep, just run pkill sshd. The problem is separating the main SSH daemon from the per-connection ones, and leaving that one alive.

A simple workaround for that would be to shut down the server, kill the remaining per-connection processes, and then restart the server, e.g. on a systemd system:

systemctl stop sshd
pkill sshd
systemctl start sshd

Or, given that sshd is probably set up to write a PID file, we can read the PID of the main process from there, and skip that. On my Debian with systemd, it's written in /run/sshd.pid but it could be set to something else in /etc/ssh/sshd_config with the PidFile option.

pgrep gives the output one PID per line, so we can use grep to remove the line with the main PID (grep -x should be used to avoid partial matches):

#!/bin/bash
mainpid=$(cat /run/sshd.pid)
pids=$(pgrep sshd | grep -vxe "$mainpid")
kill $pids

The unquoted expansion of $pids splits the string on whitespace so kill gets the PIDs separately.

You'd have to run that as root, since there's actually two per-connection processes: one running as root, one as the logged-in user. Or, if you want to just kill the sshd processes owned by your user, use pgrep -u username sshd.