AutoSSH

autossh

#!/bin/bash

# Default settings
hostname=server.example.com
port=22
keep_alive_interval=300
keep_alive_count_max=2
backoff=30

user=user
id_rsa=/home/user/.ssh/id_rsa

pid=""
pidfile=/var/run/autossh.pid

logfile=/var/log/autossh.log
log_to_console=true

# Consume configuration file
configuration=/etc/default/autossh
[ -e $configuration ] && source $configuration

### ### ### ###

log() {
    echo "[`date`] $1" >> $logfile
    if $log_to_console; then
        echo $1 >&2
    fi
}

# Trap signals
trap "on_exit" EXIT
trap "on_sigterm" SIGTERM SIGINT

on_exit() {
    [ -e $pidfile ] && rm -f $pidfile
}

sig_term=false
on_sigterm() {
    [ -n "$pid" ] && kill $pid
    sig_term=true
}

### ### ### ###

# Check if key file is available
if [ ! -e $id_rsa ]; then
    log "SSH rsa key not installed, aborting."
    exit 1
fi

# Create pid file
if ! echo $$ > $pidfile; then
    log "Failed to create pid file, aborting."
    exit 1
fi

function run_ssh() {
    ssh -R 0:localhost:22 -p ${port} -T -N \
        -o "PasswordAuthentication=no" \
        -o "User=${user}" \
        -o "IdentityFile=${id_rsa}" \
        -o "TCPKeepAlive=yes" \
        -o "ServerAliveInterval=${keep_alive_interval}" \
        -o "ServerAliveCountMax=${keep_alive_count_max}" \
        ${hostname} | tee -a ${logfile} 2>&1
    return ${PIPESTATUS[0]}
}

# Run reverse ssh tunnel
log "Starting ..."
while ! $sig_term; do
    run_ssh &
    pid=$!
    wait $pid
    log "Stopped with exit code: '$?'"
    $sig_term && exit 0

    log "Restarting autossh after '$backoff' secconds."
    delay=$backoff
    while [ $delay -gt 0 ] ; do
        sleep 1
        ((delay -= 1))
        $sig_term && exit 0
    done
done