I am a new Linux system user and I using CentOS Linux on server. How can I find the process ID (PID) of a running program on Linux based system using shell prompt?

A PID is an acronym for process identification number on Linux or Unix-like systems. It is nothing but an identification number that is automatically assigned to each process when it is created.

You can use pidof utility to find the process id’s (PIDs) by name. Please note that the pidof command only works on Linux based system, Unix user either try ps command or pgrep command to find the pid of a running program.

Purpose

Find the process ID of a running program by name on Linux.

Syntax

The basic syntax is as follows:

pidof command

OR

pidof program

OR

pidof [options] program1 program2 ... programN

NOTE: You may need to run this program as root user to find and kill pid of privileged programs.

pidof command examples

To find pid of lighttpd process, enter:
$ pidof lighttpd
Sample outputs:

Get only one pid of a program named php5-cgi

By default pidof displays all pids of named command/program:
$ pidof php5-cgi
Sample outputs (see fig.01):

2427 2426 2424 2423 2418 2387 2386 2385 2384 2383 2241 2240 2238 2237 2223

To display only one pid of the program pass the -s option as follows:
$ pidof -s php5-cgi
Sample outputs (see fig.01):

2427

Get pids of scripts

The pidof command will not display pids of shell/perl/python scripts. To find the process id’s of shells running the named script called featch-data, pass the -x option:
$ pidof -x fetch-data

Omit processes

You can ask pidof commmand to ignore or omit processes with that process id. This is useful to ignore calling shell or shell script or specific pid. In this example, find all pids of lighttpd but omit pid # 4242:
# pidof -o 4242 lighttpd
You can use the special pid %PPID to name the parent process of the pidof program in shell scripts:

#!/bin/bash
# please ignore our pid and get all pids of lighttpd on server
list=$(pidof -o %PPID lighttpd)
 
# .. now  do something on all pids stored in $list
for p in $list
do
  echo "Killing $p..."
  kill -TERM $p
done

Find pid of a program and kill it

In this example, find all PIDs of nginx server and kill it:

p=$(pidof nginx)
kill $p

Find pids of firefox and kill it focefully as the browser has stuck/frozen using kill command

p=$(pidof firefox)
kill -9 $p

pidof command options

From the pidof(8) command man page:

See also

• pidof(8) Linux/Unix command man page