Stop sshd and kill ongoing connections

Question

Under certain conditions, I want the sshd daemon to be stopped. When I do this, I want the currently open connections to be stopped too. By default, the sshd service does not kill existing connections when it stops.

Is this configurable? Can I setup sshd so that whenever it is stopped, open connections will be stopped too?

What are the alternatives? Simply killall sshd?

score 2 · Answer 1 · answered Oct 25 '19 at 12:02

Indeed, sshd service does not close active sessions while shutting down.

With a killall sshd, you would be shutting down your own sshd server as well, which is no big deal if it is already stopped, though may be risky, working from a remote station.

To avoid this, I would first locate PIDs for sshd instances bound to a client:

# who am i
root     pts/0        2019-10-25 13:52 (1.2.3.4)
# ps fxww|grep pts/
12144 ?        Ss     0:00  \_ sshd: root@pts/0
12150 pts/0    Ss     0:00  |   \_ -bash
12205 pts/0    R+     0:00  |       \_ ps fxww
12206 pts/0    S+     0:00  |       \_ grep pts/
12169 ?        Ss     0:00  \_ sshd: root@pts/1
12175 pts/1    Ss+    0:00      \_ -bash

Now I know I can kill 12144 or 12169 closing existing sessions. COnsidering that my session is attached to pts/0, I would probably avoid killing 12144.

To automate this:

exclude=`who am i | awk '{print $2}'`
ps axww | grep -v "$exclude" \
    | awk '/sshd: [^ ]*@pts/{print $1}' \
    | while read pid;
        do
            kill $pid
        done

Stop sshd and kill ongoing connections

1 Answers1