I used to wonder how can I find all the PID’s used by a specific user in the system or an application. This is a long time question in my mind. I used to try all sorts of commands to find what process is running by a service/user. The workaround commands which I used are as follows.

1.#ps -ef

2.#top

But none of these tools gives a number of processes run for an Application or a User.

That’s where I come across one wonderful command. To serve the purpose there is a command in Linux called pgrep(process grep). The grep command greps content in a file whereas pgrep greps process from proc file system. Let us have a look at pgrep usage.

Syntax of pgrep command in Linux

#pgrep application-name

Example1: Suppose we want to find what PID’s are used by firefox application.

# pgrep firefox

Output:

4000
4008

Example2: Suppose you need process run by a user then use below command

#pgrep -u user-ID

Example:

#pgrep -u 1000

Where 1000 is the user ID for a user

Sample output

1602
1621
1651
1654
1655
1660
1663
1669
1673
1678
1685
1686
1688

Example3: The above output just gives PID’s one each in the line. How about giving process details as well? We can use -a to list the process details as well.

Example:

root@linuxnix:~# pgrep nginx -a
30615 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
30618 nginx: worker process    

Example4: To list only PID’s but with different separator other than the new line, we can use -d to specify the delimiter.

Example:

root@linuxnix:~# pgrep -U 0 -d,

1,2,3,5,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,28,29,30,31,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,68,81,82,121,122,123,124,125,126,127,128,129,130,131,485,516,537,538,618,626,629,642,646,648,650,651,656,665,697,748,771,1274,1275,1280,1283,1297,1307,1310,1312,1342,1367,1407,1413,1534,1691,2889,4044,4046,4051,4105,4121,4131,4141,4174,4290,4332,23962,23963,30615,30629,31150

Example5: If we just want to list a number of the process used by a user instead of listing all the PID we can use count option.

Example:

root@linuxnix:~# pgrep -U 0 -c
103

And There are many options for this command explore your self by using man pages.

#man pgrep

In our next post, we will see about other process related command called pmap.

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Surendra Anne

Mr Surendra Anne is from Vijayawada, Andhra Pradesh, India. He is a Linux/Open source supporter who believes in Hard work, A down to earth person, Likes to share knowledge with others, Loves dogs, Likes photography. He works as Devops Engineer with Taggle systems, an IOT automatic water metering company, Sydney . You can contact him at surendra (@) linuxnix dot com.