#!/bin/bash

# Alastair Munro 31 Oct 2013
#
# Nagios plugin to report time difference as received via SNMP compared to the local time.
# The time checks are done using utc, so it should handle time differences and daylight saving
# without alarming. Make sure the machine this script runs on (poller/nagios host) is properly
# setup with ntp.
#
# Note: all date commands must be run specifying -u (utp) to prevent local timezone shifts 
# on the nagios server.
#
# Nagios exit status:
# 0 OK
# 1 Warning
# 2 Critical
# 3 Unknown

# Some defaults
community="public"
version="2c"
critical="120"
warning="60"

usage() {
   echo "Usage: $0 [-h] -H host [-C community] [-w warning] [-c critical] [-v -snmp-version]"
   echo ""
   echo "Defaults:"
   echo "community: $community"
   echo "warning: $warning"
   echo "critical: $critical"
   exit 0
}

exit_unknown() {
   echo "TIME UNKNOWN|"
   exit 3
}

readargs() {
   while getopts "hH:C:w:c:v:" arg; do
     case $arg in
        h) usage ;;
        H) host=$OPTARG ;;
        C) community=$OPTARG ;;
        w) warning=$OPTARG ;;
        c) critical=$OPTARG ;;
        v) version=$OPTARG ;;
        ?) exit_unknown ;;
     esac
   done
}

getandprintresults() {
#  Get local and remote time at the same time, so we can do a diff later. Local in utc.
   rdatestring=$( snmpget -v $version -t 60 -c $community $host HOST-RESOURCES-MIB::hrSystemDate.0 2> /dev/null | gawk '{print $NF}' )
   ldate=$(date -u)

   [ ! "$rdatestring" ] && exit_unknown

   #echo $rdatestring # debug

   rdate=$(echo $rdatestring | awk -F',' '{print $1,$2}')
   hhdiff=$(echo $rdatestring | awk -F',' '{print $3}'|awk -F':' '{print $1}')
   mmdiff=$(echo $rdatestring | awk -F',' '{print $3}'|awk -F':' '{print $2}')

#  Invert the time difference so we can calculate to utc
   if [ "$(echo $hhdiff|cut -c1-1)" == "+" ]
   then
      hhdiff=$(echo $hhdiff|sed 's/\+/\-/')
   else
      hhdiff=$(echo $hhdiff|sed 's/\-/\+/')
   fi

#  Add the + or - to the minute amount
   mmdiff="$(echo $hhdiff|cut -c1-1)$mmdiff"

   #echo $rdate #debug
   rdate=$(date -u -d "$rdate")
   #echo $rdate #debug
   #echo $hhdiff #debug
   #echo $mmdiff #debug
   #echo "L: $ldate" #debug
   #echo "R: $rdate" # debug
   #rdateu=$(date -u -d "$rdate $hhdiff hours $mmdiff minutes") # debug
   #echo "Ru: $rdateu" # debug

   lepoc=$(date -u "+%s" -d "$ldate")
   repoc=$(date -u "+%s" -d "$rdate $hhdiff hours $mmdiff minutes")
   difference=$(($repoc - $lepoc))

#  A second either way is probably network latency and checking just before the second changes
#  Thus set to 0
   [ $difference -eq 1 ] && difference=0
   [ $difference -eq -1 ] && difference=0

#    If the calculated difference is negative, make it positive again for comparison.
#   difference=$(($rdate_s - $ldate_s))
   if [ "$difference" -lt 0 ] ; then
     positivedifference=$(($difference*-1))
   else
     positivedifference=$difference
   fi

   if [ "$positivedifference" -gt "$critical" ] ; then
     echo "TIME CRITICAL - Time difference = ${difference}s|diff=$difference"
     exit 2
   fi

   if [ "$positivedifference" -gt "$warning" ] ; then
     echo "TIME WARNING - Time difference = ${difference}s|diff=$difference"
     exit 1
   fi

   echo "TIME OK - Time difference = ${difference}s|diff=$difference"
   exit 0
}

# The calls to the different functions.
readargs "$@"
[ ! "$host" ] && exit_unknown

getandprintresults