Don’t feel like shelling out $$$ for NewRelic or Blackfire.io? Got a micro instance hosting a blog that nobody reads that doesn’t have the memory to support enterprise monitoring anyway (*cough* this blog *cough*)?

Here’s a shell script that will email you when server load gets above whatever threshold you specify. Would be pretty easy to adapt to monitor memory using the ‘free‘ command as well. Just schedule it using ‘crontab -e‘, like ‘*/5 * * * * /path/to/script.sh‘ for every 5 minutes, and you’re set.

Server load monitoring on a budget!

#!/bin/bash
# requires bc library - yum install bc

# config
# alert threshold, as decimal
ALERT=.7; # 70% CPU utilization
# admin email
EMAIL='[email protected]';

# add /usr/bin to path so cron works
export PATH=$PATH:/usr/bin;

# get number of processors
NPROC=`nproc`;
# get first utilization metric
UTIL=`cat /proc/loadavg | cat -d ' ' -f 1`;

# divide util by number of processors, accounting for 0.00 util
RESULT=`bc <<< "scale = 2; $UTIL / $NPROC"`; 

# email alert if util is greater than alert threshold 
if [[ `bc <<< "$RESULT > $ALERT"` -eq 1 ]]
then
  # calculate a percentage
  PERC=`bc <<< "scale = 2; $RESULT * 100"`;
  echo "CPU utilization is above threshold at $PERC %";
  # add top output to email
  TOPOUTPUT=`top -n 1 -b`;
  `/usr/bin/mailx -s "Utilization high on $HOSTNAME" -r "$EMAIL" "$EMAIL" <<< "CPU on $HOSTNAME is at $PERC % 

$TOPOUTPUT"`;
# else
  # echo "Utilization is only $RESULT";
fi

You can test it by generating CPU load with the stress utility if you like.