This document describes a shell script that monitors CPU utilization on a Linux server. The script checks CPU usage every 15 minutes using the 'top' utility. If usage exceeds 75% but is less than 85%, it sends a warning to the administrator and users of the top 10 processes. If usage goes above 85%, it kills the top process and notifies the user. The script runs in the background via cron, and technical details are provided on how it extracts CPU usage and process details.

1. ATHLONE IT SHELL SCRIPT PROJECT 3.2
Monitoring CPU
Utilization on LINUX
By controlling users processes
Dmitrijus Ponomarenko
4/28/2014

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Contents
Purpose of Program...................................................................................................................... 2
Description...................................................................................................................................2
Technical Description.................................................................................................................... 2
User Manual.................................................................................................................................6
Other Information ........................................................................................................................ 8

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Purpose ofProgram
The general idea of this project is to create a shell script which will monitor CPU usage in the
background and once it exceeded 75% it should make the action to minimize the CPU
utilization. To achieve this I wrote the shell script which should monitor CPU usage utilized
by users of Linux server.
Description
Every 15 minutes the script should check the CPU usage and if it is higher than 75% but less
than 85% it should send warning message to the administrator’s email with an attachment
of the top 10 processes and to each user of top 10 processes asking them to shut down the
running process. If the CPU usage exceeded 85%, then the script should find top 10
processes, copy them and send to them to the administrator’s email. Then, the script should
kill the first of the user’s top processes and send the information of each killed process to
the user’s email. If CPU utilization is still too high the script should repeat this action with
the second process and so on until the CPU utilization is below the limit.
To run the shell script on the background I used the utility named Cron. Crontab is a time-
based scheduler in Unix-Linux operating system.
Technical Description
This project was created by using shell script. A shell script is a computer program designed
to be run by the Unix shell, a command line interpreter.
The first line of the script indicates which interpreter should execute the rest of the script
(#!/bin/sh).
To find the CPU usage utilized by the users I used the `top` utility. Top provides an ongoing
look at processor activity in real time. It displays a listing of the most CPU-intensive tasks on
the system.

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From the `top` utility output, see above, I need to extract information about CPU usage and
the 10 top processes. To do that I used commands such as:
cpu=`top -d 0.5 -b -n2 | grep "Cpu(s)"|tail -n 1 | awk '{print $2}'`
Where -d specifies the delay between screen updates (-d 0.5 sec), -b is used to send the
output from `top` to next the program -n represent number of iterations requested (-n2).
Grep is a command-line utility for searching plain-text data sets for lines matching a regular
expression (grep "Cpu(s)"). This is the output after first two commands:
Next command (tail -n 1) says, give me a bottom line (only after update we get real cpu
utilization) and the last command says give me a second argument of this line and assign it
to the variable `cpu`. So the output that we should get is:
cpu=1.9%us,
The Next command I used to extract the whole number from the first commands line output
(1.9%us,) and assign it to the variable.
let cpu_usage=`echo $cpu | cut -f1 -d'.'`
The cpu_usage=1
Both this commands are represent a function called cpu_stat.
function cpu_stat() {
cpu=`top -d 0.5 -b -n2 | grep "Cpu(s)"|tail -n 1 | awk '{print $2}'`
let cpu_usage=`echo $cpu | cut -f1 -d'.'`
}

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To get top 10 processes running on the system and save output in the file I used command
as:
top -b -n 1 | sed -e "1,6d" | head -11 >> file_name
This command says, give me the output of first iterations and pass it to the next command.
The second command (sed -e "1,6d" ) should remove first six line from the previous
command output and pass it to the last command which should cut top 11 lines and save
output to the file.
See output of 10 top processes below:
Another very important Linux utility used in this program is the mail utility. Mail utility
allows it to send emails through the command line and also send emails with attachments.
To send contents of a file (such as /path /to/message) as a mail body to the each of
registered user, I used the following syntax:
$ mail -s 'Test' test@gmail.com < /path /to/message
All information about registered users stored in the file called users_info.txt. This file
contains the information’s about all registered users, such as usernames and email
addresses. Program using this file to compare usernames of running processes with the
usernames in the file and if they match make an action, such as sending warning messages
or killing processes.
File users_info.txt

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Also in this script I used: logical condition such as ( if-elif-else, while, while read), logical
operators such as (and, or, not), arithmetic such as ( let ) and functions.
cron
To run the shell script in the background I used the utility named Cron. Cron is a Unix, Linux
utility that allows tasks to be automatically run in the background at regular intervals by the
cron daemon. These tasks are often termed as cron jobs in Unix , Linux. Crontab (CRON
TABle) is a file which contains the schedule of cron entries to be run and at specified times.
Crontab file:
A crontab file has five fields for specifying day , date and time followed by the command to
be run at that interval.
* * * * * command to be executed
- - - - -
| | | | |
| | | | +----- day of week (0 - 6) (Sunday=0)
| | | +------- month (1 - 12)
| | +--------- day of month (1 - 31)
| +----------- hour (0 - 23)
+------------- min (0 - 59)
Crontab example:
A line in crontab file like below removes the tmp files from /home/someuser/tmp each day at
6:30 PM.
30 18 * * * rm /home/someuser/tmp/*
To set up new crontab or edit current crontab, used command 'crontab -e', display current
crontab 'crontab -l', delete current crontab 'crontab -r'.

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User Manual
This program can be executed in two ways. First way is to run the program manually using
the command line, the second way is to run program using cron utility.
Run Manually
In this method (use file called cpu_monitor_test1.sh), script is executed through command
line by using 'bash' command.
1. change directory to directory contained executed file
2. use bash to execute shell file
3. if CPU usage exceeded 75% the program will display and send to administrator cpu
statistic and top 10 processes

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4. also the script will display and send warning message to the each user of the top
processes
5. if cpu usage exceeded 90% the script should kill the top process and display a send
message to the process user
Using cron
To run script in the background (use file called cpu_monitor_test2.sh) at a specific period of
time we need set up the crontab file. In the file we need to specify a day, date and time
followed by the command to be run at that interval.
1. run 'crontab -e' command to set up new crontab file

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2. specify time and command (for example run every 15 minutes) and save the file
After that the cron will run the script every 15 minutes 24/365.
Other Information
To run the script fromotherPCs youshouldchange all pathsto the file dependingof directoryon
whichyoulocate executedfiles.