#!/bin/bash
# Script to check free memory, logging it, and if it is below a configured
# min value, mailing an alert.  Typical usage is to schedule a cron job to
# run this regularly.
#
# Assumes free -m output formatted like:
#              total       used       free     shared    buffers     cached
# Mem:           538        525         13          0         47        342
# -/+ buffers/cache:        135        403
# Swap:         1023         35        988


# Feel free to edit these configuration values
memoryMin=200
emailFrom=memlow
emailTo=root
logSummary=/var/log/memlow.log
logDetails=/var/log/memlow_details.log

# Compute some values
now=`date +'%Y/%m/%d__%H:%M:%S'`
fullReport=`free -m`
# Note:  Do not try to reuse fullReport here as:
#          memoryFree=`echo -e $fullReport | grep buffers/cache | awk ...
#        It loses the newlines and tries to assign "shared" (the fourth 
#        column header) to fullReport.  Have to re-execute free -m instead,
#        which is unfortunate because the numbers can change slightly.
memoryFree=`free -m | grep buffers/cache | awk -F'  *' '{print $4}'`

# Generate the log files
echo -e "$now Free memory is $memoryFree MB"     >> $logSummary
echo -e "\n$now Output of free -m:\n$fullReport" >> $logDetails

# Conditionally send e-mail
if [ $memoryFree -lt $memoryMin ]; then
   echo -e "Free memory is low on $HOSTNAME at $now: $memoryFree MB (less than $memoryMin) \n\n\n $fullReport\n\n\nSee $logSummary for historical trend of values.\nSee $logDetails for detailed history." | mail -s "Memory is low ($memoryFree) on $HOSTNAME at $now" -r $emailFrom $emailTo
fi