tunnelhome

#!/bin/sh
# This script was written to run under the busybox ash shell.
#
# Start a ssh reverse tunnel daemon back to the base server.

SSH_USER=probe1
SSH_PROXY_PORT=22201
SSH_HOST=foo.bar
SSH_KEYFILE=/root/.ssh/id_rsa
RECOVER_WAIT=10
SSH_SAI=15 # ServerAliveInterval
SSH_SACM=4 # ServerAliveCountMax

PIDFILE="/tmp/$(basename $0.pid)"
MYNAME=$(basename $0)
DEPENDENCIES="ssh netstat pgrep"

#--

echoerr() {
        # Print errors to stderr.
        echo "$@" 1>&2;
}

f_start() {
    # FIXME: Test for openssh clinent. Won't work with dbclient.
    #
    # Verify dependancies.
    for EACH in $DEPENDENCIES ; do
        DEP_TARGET=$(which $EACH 2> /dev/null)
        if [[ -z "$DEP_TARGET" ]] ; then
            DEP_FAIL=1
            echoerr ""
            echoerr "ERROR: $EACH not found."
        fi
        if [[ "$DEP_FAIL" == 1 ]] ; then
            echoerr ""
            echoerr "At least one required dependency is missing. Quitting."
            echoerr ""
            return 1
        fi
    done
    # Verify the keyfile's existence.
    if [[ ! -f "$SSH_KEYFILE" ]] ; then
        echoerr ""
        echoerr "ERROR: SSH_KEYFILE not found: $SSH_KEYFILE. Quitting."
        echoerr ""
        return 1
    fi
    # Bail out if the lockfile/PIDFILE already exists.
    if [[ -r "$PIDFILE" ]] ; then
        echoerr ""
        echoerr "ERROR: Already running at PID $(cat $PIDFILE)? Quitting."
        echoerr ""
        return 1
    fi
    echo ""
    echo -n "Starting daemon: "
    ( while true ; do
        # Wait until the network is up.
        if [[ $(netstat -rn | egrep "^0\.0\.0\.0" | wc -l) -lt 1 ]] ; then
            echoerr "Network not ready."
            sleep 3
            continue
        fi
        # Add timeout for ssh command?
        # How will we know that the tunnel is really up? Can we test that? How do we kill a bad tunnel?
        # dropbear sucks # dbclient -K 15 -I 0 -i $SSH_KEYFILE -N -R $SSH_PROXY_PORT:localhost:22 $SSH_USER@$SSH_HOST
        # FIME: Consider using autossh.
        echoerr "Starting tunnel."
        ssh -i $SSH_KEYFILE -o "ServerAliveInterval=$SSH_SAI" -o "ServerAliveCountMax=$SSH_SACM" -N -R $SSH_PROXY_PORT:localhost:22 $SSH_USER@$SSH_HOST
        X_SSHTUNNEL=$?
        echoerr "SSH tunnel quit with exit:$X_SSHTUNNEL"
        echoerr "Restarting in $RECOVER_WAIT seconds."
        sleep $RECOVER_WAIT
    done ) &> /dev/null &
    MYPID=$!
    echo "Done."
    echo "Running at PID $MYPID."
    echo "$MYPID" > $PIDFILE || (echoerr "ERROR: can't write to PIDFILE. Killing daemon." ; f_stop ; return 1)
    # Disown neither needed or available in busybox ash shell.
    # disown $MYPID
    echo ""
}

f_stop() {
    if [[ -r "$PIDFILE" ]] ; then
        echo ""
        echo -n "Stopping daemon: "
        MYPID=$(cat $PIDFILE)
        MYPID_CHILDREN=$(pgrep -P $MYPID)
        kill "$MYPID" || echoerr "Error trying to kill PID: $(cat $PIDFILE)"
        for EACH in $MYPID_CHILDREN ; do
            kill "$EACH"
        done
        rm -f "$PIDFILE"
        echo "Done."
        echo ""
    else
        echo ""
        echo "No PIDFILE found."
        echo ""
        return 2
    fi
}

#--

case "$1" in
    start)
        f_start
    ;;
    stop)
        f_stop
    ;;
    *)
        echo ""
        echo "Usage: $MYNAME start|stop"
        echo ""
        exit 1
    ;;
esac