autossh.sh

#!/usr/bin/env sh

CHECK_INV=600

REMOTE_USER='remote_user'
REMOTE_PORT=22
REMOTE_HOST='example.com'

DST_PORT=22
SRC_PORT=2222
PRIVATE_KEY='/home/local_user/.ssh/id_rsa'

SSH_CMD="ssh -NfR "$SRC_PORT:localhost:$DST_PORT" -i $PRIVATE_KEY $REMOTE_USER@$REMOTE_HOST";
SSH_CHK="ssh -p $REMOTE_PORT -i $PRIVATE_KEY $REMOTE_USER@$REMOTE_HOST \"netstat -an | egrep 'tcp.*:$SRC_PORT.*LISTEN'\" > /dev/null 2>&1";

while true;
do
    $SSH_CHK;
    if [ $? -ne 0 ];
    then
        killall -9 ssh;
        $SSH_CMD;
    fi
    sleep $CHECK_INV;
done