HOWTO autossh and knockd

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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 etablish a new connection.

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.

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