How to Monitor Server memory Using Shell Script


Author - Sanjay


Almost all linux admin knows about bash and bash scripting is one of the most demand skills for any linux admin . So today we will understand onitor Server memory Using Shell Script in your linux systems .

RAM is considered as one of the most important part of any system , especially when a system runs in production and you need to consistently monitor your RAM usage .

We will be writing a shell script to monitor and alert around this special part of your linux server . I have mostly used Linux VPS and has been using it with Ram of 1GB .

##Pre-Requisistes A CentOS/RHEL 7 production server or a Linux VPS with mailx utility installed working on your server.

Environment Setup

lets create a file using vi editor


Now we are going to use this to run and send mail alerts for our RAM usage .So the logic that we are going to write in this script is if memory usage is more than a particular limit let's say in our case 500MB . We are going to send an email alert with list of top 5 processess consuming high memory in our server . Lets follow the step below

1.1 Find Free Memory Of your Linux Server

In order to find free memory of your linux server execute the following command .

free -mt

This command below shows the total free available and total memory in your server as shown below .

              total        used        free      shared  buff/cache   available
Mem:            991         214         543           6         232         634
Swap:           819           0         819
Total:         1811         214        1363

Now we want to extract the free memory available here and proceed with our calculation based on that .Here is how we do that

free -mt | grep Total | awk '{print $4}'

This returns 1363 as output . Now next step is finding out what all processess consuming higher percentage of memory .

1.2 Find Process Consuming high amount of Memory

we will now list down only top 5 processess consuming memory using ps command.

ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem  | awk 'NR<=6'

We will get output as below which is list of processes consuming memory and cpu .

  PID  PPID CMD                         %MEM %CPU
 1116     1 /usr/bin/dockerd -H fd:// -  7.0  0.1
 1115     1 /usr/bin/containerd          3.8  0.0
  713     1 /usr/bin/python2 -Es /usr/s  2.9  0.0
 1106     1 /usr/bin/python2 -Es /usr/s  1.7  0.0

Next step would be we will be storing this in a file and sending a mail alert .

1.3 Sending email

We now will be sending email alert , here is the consolidated shell script which does the actual work of sending mail .Here is the consolidated script that does the hard work.

subject="Memory Alert"

free=$(free -mt | grep Total | awk '{print $4}')

if [[ "$free" -le 100  ]]; then
ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | awk 'NR<=5'
    | head >/tmp/memeorydata.txt


echo -e "Warning, server memory is running low!\n\n
    Free memory: $free MB" |

mailx -a "$file" -s "$subject" -r "$from" -c "$to"

exit 0

We are getting the free memeory then calculationg if free memory is less than 100MB . If its less than the threshold we are finding out the top 5 processes consuming the memeory and storing that data in a file . We now use the ```mailx`` to send email to our email .Once you create and use the shell script make sure you make it executable . Once you make the script executable , you should set it as a cron JOB .

##Conclusion So , we have seen how we can create a shell script that sends an email alert , let us know if you have any concerns and comments on the tutorial.