Nagios- Memory Check Plugin

Dave the below code as check_mem.sh using nano and chmod it to +x. (file to be saved inside nagios libexec- such as /usr/local/nagios/libexec/check_mem.sh

#!/bin/sh

# Determine memory usage percentage on Linux servers.
# Original write for RHEL3 for PC1 Project – jlightner 05-Jul-2005
#
# Modified for RHEL5 on mailservers.
# -Some of the escapes previously required for RHEL3's ksh not needed on RHEL5.
# -Changed comparisons to allow for decimal rather than integer values.
# jlightner 23-Jan-2009
#

# Usage: check_mem.sh WARNING CRITICAL
# Where WARNING and CRITICAL are the integer only portions of the
# percentage for the level desired.
# (i.e. 85% Warning & 95% Critical should be input only as "85 95".)

# Define Levels based on input
#
WARNLEVEL=$1
CRITLEVEL=$2

# Setup standard Nagios/NRPE return codes
#
UNKNOWN_STATE=3
CRITICAL_STATE=2
WARNING_STATE=1
OK_STATE=0

# Give full paths to commands – Nagios can't determine location otherwise
#
BC=/usr/bin/bc
GREP=/bin/grep
AWK=/bin/awk
FREE=/usr/bin/free
TAIL=/usr/bin/tail
HEAD=/usr/bin/head

# Get memory information from the "free" command – output of top two lines
# looks like:
# total used free shared buffers cached
# Mem: 8248768 6944444 1304324 0 246164 5647524
# The set command will get everything from the second line and put it into
# posiional variables $1 through $7.
#
set `$FREE |$HEAD -2 |$TAIL -1`

# Now give variable names to the positional variables we set above
#
MEMTOTAL=$2
MEMUSED=$3
MEMFREE=$4
MEMBUFFERS=$6
MEMCACHED=$7

# Do calculations based on what we got from free using the variables defined
#
REALMEMUSED=`echo $MEMUSED – $MEMBUFFERS – $MEMCACHED | $BC`
USEPCT=`echo "scale=3; $REALMEMUSED / $MEMTOTAL * 100" |$BC -l`
#USEPCT=`echo scale=3 "\n" $REALMEMUSED \/ $MEMTOTAL \* 100 |$BC -l |$AWK -F\. '{print $1}'`

# Compare the Used percentage to the Warning and Critical levels input at
# command line. Issue message and set return code as appropriate for each
# level. Nagios web page will use these to determine alarm level and message.
#
#if [ `echo "5.0 > 5" |bc` -eq 1 ]
#then echo it is greater
#else echo it is not greater
#fi
if [ `echo "$USEPCT > $CRITLEVEL" |bc` -eq 1 ]
then echo "CRITICAL – Memory usage is ${USEPCT}%"
exit ${CRITICAL_STATE}
elif [ `echo "$USEPCT > $WARNLEVEL" |bc` -eq 1 ]
then echo "WARNING – Memory usage is ${USEPCT}%"
exit ${WARNING_STATE}
elif [ `echo "$USEPCT < $WARNLEVEL" |bc` -eq 1 ]
then echo "OK – Memory usage is ${USEPCT}%"
exit ${OK_STATE}
else echo "Unable to determine memory usage."
exit ${UNKNOWN_STATE}
fi
echo "Unable to determine memory usage."
exit ${UNKNOWN_STATE}

Then in nrpe.cfg or if you're using icinga place it in the command.cfg file on each host I have something like:

# MEMORY Check
# check_mem <WARN%> <CRIT%> = MEMORY at defined warning and critical use %.
command[check_mem]=/usr/local/nagios/libexec/check_mem.sh 85 95

On your Nagios master you would then need to modify service.cfg to include something like:

define service{
use generic-service
host_name BILLYBOB
service_description # Memory Use Pct
contact_groups ux-admins, noc-op
check_command check_nrpe!check_mem
}

Src: http://www.linuxquestions.org/questions/linux-software-2/nagios-check-ram-usage-on-remote-server-747531/