Create a ssh tunnel after network is ready on Debian/Raspberry Pi

[davideuler]

A ssh tunnel could be created in /etc/rc.local. As following:

vim /etc/rc.local

timeout=5
ssh -p 22 -o BatchMode=yes -o ConnectTimeout=3 -i /data/david/xxx.pem -fCNR 7280:localhost:22 root@101.20.5.6

while test $? -gt 0
do
   sleep 3 # highly recommended - if it's in your local network, it can try an awful lot pretty quick...
   echo "Trying again..."
   ssh -p 22 -o BatchMode=yes -o ConnectTimeout=3 -i /data/david/xxx.pem -fCNR 7280:localhost:22 root@101.20.5.6
   TIMEOUT=$((TIMEOUT-1))
   if [ $TIMEOUT -eq 0 ]; then
        echo "timed out"
        # error time out
        exit 1
   fi
done

sleep 3

Here the -o BatchMode=yes means the SSH connection will fail immediately if the key is rejected, instead of failing back to a password prompt. The ConnectionTimeout the timeout for ssh command, so it would not wait for a long time.

Note that for Debian 9/10/11, rc.local would not run by default.
You need to make the script executable, and also enable the service.

chmod +x /etc/rc.local
systemctl start rc-local
systemctl enable rc-local