HOWTO_autossh_and_knockd

About

If you want to use knockd on your server and autossh on your client you get the problem that autossh is not able to knock the server before establish a new connection.

Install

You can use a wrapper ssh script to solve this. Place this script in a path where the original ssh-binary is not and not in the $path, for example in /etc/ppp, replace $YOURSERVER and $KNOCKSEQUENCE

#/bin/bash
PID=/var/run/ssh_wrapper.pid
test -e $PID && kill -9 `cat $PID` ; rm $PID
knock $YOURSERVER $KNOCKSEQUENCE
/usr/bin/ssh $@ &
echo $! > $PID

Now tell autossh to use this wrapper, and start autossh

export AUTOSSH_PATH=/etc/ppp/ssh
autossh ...

At this time on every connection autossh calls the wrapper-script. The wrapper knocks the server and then call the original ssh-binary.