#!/bin/sh 
#
# Program: Verify that a DNS server is answering queries <dns-check>
#
# Author: Matty < matty91 at gmail dot com >
#
# Current Version: 1.0
#
# Revision History:
#
#  Version 1.0
#    Initial Release
#
# Last Updated: 08-14-2006
#
# Purpose:
#   The dns-check shell script can be used to verify that a DNS server is 
#   reponding to queries. If a server fails to resolve a name through DNS,
#   an E-mail is sent to the administrator listed in the $ADMIN variable.
#
# License:
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
#
# Installation:
#   Copy the shell script to a suitable location
#
# Usage:
#   dns-check takes a a file that contains one or more entries
#   in the following format:
#         DNS_SERVER_IP  DNS_ENTRY  RECORD_TYPE
#
# Example:
#   $ cat dns-check-servers
#   192.168.1.1 mail.fooby.net A
#
#   $ dns-check -f dns-check-servers

# Default user to send E-mail to
ADMIN="root"

# Paths to various binaries
DIG="/usr/sbin/dig"
GREP="/usr/bin/grep"
LOGGER="/usr/bin/logger"
MAIL="/usr/bin/mailx"

# Useful functions
usage () {
        echo "Usage: $0 [ -e EMAIL_ADDRESS ] -f LIST OF SERVERS"
        echo "       -e address   : address to send alarms to"
        echo "       -f site file : file with list of sites and record types"
}

# If no options are provided, print a help screen
if [ $# -eq 0 ]
then
        usage
        exit 0
fi

# Parse the options that are passed to the script
while getopts e:f: option
do
        case "${option}"
        in
                e) ADMIN=${OPTARG} ;;
                f) SITES=${OPTARG} ;;
                \?) usage
                    exit 1;;
        esac
done

# Check to make sure the utilities are present
if [ ! -f ${DIG} ] || [ ! -f ${MAIL} ] || [ ! -f ${LOGGER} ] || [ ! -f ${GREP} ] 
then
        echo "ERROR: Cannot find the dig, mail, logger or grep utility"
        usage
        exit 1
fi

# Verify that a file was passed as an argument
if [ ! -f ${SITES}  ]
then
        echo "ERROR: No options specified"
        usage
        exit 1
fi

# Cycle through the file and send E-mail if a server isn't functioning.
cat ${SITES} | while read SERVER RECORD TYPE
do
        # Make sure all entries have three values listed
        if [ "${SERVER}" = "" ] || [ "${RECORD}" = "" ] || [ "${TYPE}" = "" ]
        then
                echo "ERROR: Trouble processing \${SERVER}\, \${RECORD} or \${TYPE}"
                exit 1
        fi

        # Grab the specified record from the server, and make sure it returns valid data.
        ${DIG} @${SERVER} ${RECORD} ${TYPE} > /dev/null 2>&1 

        # See if the return code is zero.
        if [ $? -ne 0 ]
        then
            ${LOGGER} -p daemon.notice "Unable to resolve ${RECORD} on server ${SERVER}"
            echo "Unable to resolve ${RECORD} on server ${SERVER}" \
                 | ${MAIL} -s "Unable to resolve ${RECORD} on server ${SERVER}" ${ADMIN}
        fi
done

exit 0