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Linux: Check if program is running with bash shell script


Leon
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This is an example of a bash script which checks for some running process (daemon or service) and does specific actions (reload, sends mail) if there is no such process running.

 

Requirements:

Any modern Linux or OSX distribution

Nearly any unix sistem with recent bash version, grep, ps

We call ps (process list) command to list every system process and then use grep(filter) command to check if our process name is in that list, for example:

 

$ ps ax | grep httpd

592 ?? Ss 8:22.25 /usr/local/apache/bin/httpd

3706 ?? I 0:58.06 /usr/local/apache/bin/httpd

3707 ?? I 0:40.12 /usr/local/apache/bin/httpd

3708 ?? I 0:49.56 /usr/local/apache/bin/httpd

3709 ?? I 1:02.86 /usr/local/apache/bin/httpd

3710 ?? I 1:12.26 /usr/local/apache/bin/httpd

3711 ?? I 1:20.03 /usr/local/apache/bin/httpd

3712 ?? I 0:48.79 /usr/local/apache/bin/httpd

3714 ?? I 1:01.60 /usr/local/apache/bin/httpd

3715 ?? I 0:58.91 /usr/local/apache/bin/httpd

3716 ?? I 0:42.88 /usr/local/apache/bin/httpd

28363 p3 S+ 0:00.01 grep httpd

 

But if there is no such process, grep (filter) command will match itself, because command argument has exactly same string which is searched for:

 

$ ps ax | grep nosuchprocess

28372 p3 S+ 0:00.01 grep nosuchprocess

So, we have to add additional 'grep -v grep' filter that will remove process which command line contains 'grep' i.e. grep itself.

 

Here is a script wich checks if SERVICE (variable at the beginning of script which contains service name) is running, and if it's not running, mails warning message to root:

 

source code: bash script

 

#!/bin/sh
SERVICE='httpd'

if ps ax | grep -v grep | grep $SERVICE > /dev/null
then
   echo "$SERVICE service running, everything is fine"
else
   echo "$SERVICE is not running"
   echo "$SERVICE is not running!" | mail -s "$SERVICE down" root
fi

 

WARNING!!!

If you process name is too short and is substring of some other process command line, suggested approach could fail (for example, you checking for 'testd' process, but have running 'testdoo-doo-doo" which will result false positive)

Though, highly unlikely, but if your process name will begin with 'grep', suggested approach could fail

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