monitoring script checking for ssh tunnel, rebuilding it if necessary

tunnel_monitor.sh

#!/usr/bin/env sh


###########################################################################
# CONFIGURATION
##


TAP_DEV="tap0"  # TAP device configured to connect to the remote server
ETH_DEV="eth0"  # ETH device for DHCP


SRV_IP="XXX.XXX.XXX.XXX"  # public remote server IP
SRV_PT="22"        # public remote server SSH port
INTRN_IP="10.0.1.1"   # internal remote server IP


TEST_URL="http://www.google.com"  # any remote URL for testing connectivity


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


IFUP=`which ifup`
IFDOWN=`which ifdown`
SLEEP=`which sleep`
NSTAT=`which netstat`
GREP=`which grep`
DATE=`which date`
PING=`which ping`
DHCLIENT=`which dhclient`
CURL=`which curl`
PS=`which ps`


TUN_COMMAND="$DHCLIENT $ETH_DEV; $SLEEP 3; $IFDOWN $TAP_DEV ; $SLEEP 3 ; $IFUP $TAP_DEV ; $SLEEP 3"
NETSTAT_COMMAND="$NSTAT -nt | $GREP '$SRV_IP:$SRV_PT' | $GREP 'ESTABLISHED'"
PS_COMMAND="$PS -aux | $GREP '$SRV_PT'"
PING_COMMAND="$PING -c 3 -w 10 $INTRN_IP"
CURL_COMMAND="$CURL '$TEST_URL'"
MONITOR_COMMAND="$NETSTAT_COMMAND && $PS_COMMAND && $PING_COMMAND && $CURL_COMMAND"
DATE_LOG_COMMAND="$DATE --rfc-3339=seconds"


while true ; do
  printf "%s -- " "`$DATE_LOG_COMMAND`"

  eval "$MONITOR_COMMAND" > /dev/null 2>&1
  if [ $? -ne 0 ] ; then
    printf "re-building tunnel"
    eval "$TUN_COMMAND" > /dev/null 2>&1
  else
    printf "tunnel is up"
  fi

  I=0
  STEP=5
  while [ $I -le 60 ] ; do
    $SLEEP $STEP
    printf "."
    I=`expr $I + $STEP`
  done

  printf "\n"
done