#!/bin/bash
# version: 2008-08-05.01

# wassup <host>

# wassup is a simple host monitor that checks if a host is online:
#   - Pings the target host
#   - Sends an email if the host is unresponsive
#   - Creates a lockfile to prevent repeated notifications
#   - Sends an email when host is responsive again

# It is designed to be run from any location by an ordinary user, after editing
# the necessary variables below ($SAFETY, $BASEDIR, & $MAILTO).

# After testing from the command line, run from cron at desired interval:
# */5 * * * * /home/bob/wassup/wassup www.example.edu >/dev/null

# by Jorey Bump
# http://www.joreybump.com/code/wassup/

# Set local variables here:

# The safety host is a reliable external host to ping in order to prove the
# network connection is working:
SAFETY="www.example.com"

# The base directory contains lockfiles, messages and logs. It must be writable
# by the user running wassup:
BASEDIR=/home/bob/wassup

# Send email notifications to this address (if list, use commas, no spaces)
# Obviously, these accounts should be accessible if target is down
# MAILTO=bob,admin@example.com,5551234444@mobile.example.net
MAILTO=bob@example.com

#########
# It should not be necessary to edit beyond this point.
#########

# Get target host (IP address or host name argument from command line):
TARGET=$1

# Create path to lock file for target host, used to prevent repeated
# mailings:
LOCKFILE=$BASEDIR/${TARGET}.offline

# Email Subject lines:
SUBJECT_DOWN="Server is down! Cannot ping ${TARGET}."
SUBJECT_UP="Server is up again! ${TARGET} is back online."

# Paths to message files containing the bodies of the email notifications:
MESSAGE_DOWN=$BASEDIR/message_down
MESSAGE_UP=$BASEDIR/message_up

# Create path to log file for target host:
LOGFILE=$BASEDIR/${TARGET}.log

# Full date for log entries: Wed Aug 29 19:03:38 EDT 2001
LOGDATE=$(date)

# Check usage:

# Usage:
USAGE="usage = `basename $0` <ip or host>"

# Check for expected number of arguments:
if [ $# != 1 ] ; then
  printf "\n$USAGE\nwassup needs an IP address or host:\n"
  printf "wassup 192.1.1.1  or  wassup www.foo.com\n\n"
  exit 1
fi


# Begin:

# Ping the target:
ping -c 1 $TARGET

if [ $? != 0 ]
then
  # No response from target, so check the safety host to make sure we have a
  # network connection:
  ping -c 1 $SAFETY
  if [ $? = 0 ]
  then
    # The safety host responded, so ping the target again:
    ping -c 2 $TARGET
    if [ $? != 0 ]
    then
      # Still no response from target, so assume it's down.
      # Only send an alert if there is no lockfile:
      if [ ! -e $LOCKFILE ]
      then
        # There is no lockfile for this host, so sound the alert:
        echo "$LOGDATE host=$TARGET status=unreachable" >> $LOGFILE
        mail -s "$SUBJECT_DOWN" $MAILTO < $MESSAGE_DOWN
        if [ $? = 0 ]
        then
          # Log success of email notification:
          echo "$LOGDATE host=$TARGET message=alert status=sent" >> $LOGFILE
        else
          # Log Failure of email notification:
          echo "$LOGDATE host=$TARGET message=alert status=error" >> $LOGFILE
        fi
        # Create lockfile to prevent repeat notifications for this host:
        touch $LOCKFILE
      fi
    fi
  else
    # Safety did not respond, so there is a network problem on our end.
    # Log & abort:
    echo "$LOGDATE safety=$SAFETY status=unreachable" >> $LOGFILE
    exit 2
  fi
else
  # The target host responded. Check for a lockfile:
  if [ -e $LOCKFILE ]
  then
    # A lockfile exists for this host, indicating it was previously down.
    # It is now back online, so log & send notification:
    echo "$LOGDATE host=$TARGET status=online" >> $LOGFILE
    mail -s "$SUBJECT_UP" $MAILTO < $MESSAGE_UP
    if [ $? = 0 ]
    then
      # Log success of email notification:
      echo "$LOGDATE host=$TARGET message=online status=sent" >> $LOGFILE
    else
      # Log Failure of email notification:
      echo "$LOGDATE host=$TARGET message=online status=error" >> $LOGFILE
    fi
    # Remove the lockfile to reset host status:
    rm $LOCKFILE
  fi
fi

# Exit nicely:
exit 0