ps command

The ps command displays active processes.

Syntax

The syntax for the ps command is:

ps [options]

Options

Option	Description
-a	Displays all processes on a terminal, with the exception of group leaders.
-c	Displays scheduler data.
-d	Displays all processes with the exception of session leaders.
-e	Displays all processes.
-f	Displays a full listing.
-glist	Displays data for the list of group leader IDs.
-j	Displays the process group ID and session ID.
-l	Displays a long listing
-plist	Displays data for the list of process IDs.
-slist	Displays data for the list of session leader IDs.
-tlist	Displays data for the list of terminals.
-ulist	Displays data for the list of usernames.

Example

1. If you run ps command without any arguments, it displays processes for the current shell.
$ ps

List Current Running Processes

Print All Processes in Different Formats

2. Display every active process on a Linux system in generic (Unix/Linux) format.
$ ps -A
OR
$ ps -e

List Processes in Standard Format

3. Display all processes in BSD format.
$ ps au
OR
$ ps axu

List Processes in BSD Format

4. To perform a full-format listing, add the -f or -F flag.
$ ps -ef
OR
$ ps -eF

List Processes in Long List Format

Display User Running Processes

5. You can select all processes owned by you (runner of the ps command, root in this case), type:
$ ps -x

6. To display a user’s processes by real user ID (RUID) or name, use the -U flag.
$ ps -fU tecmint
OR
$ ps -fu 1000

List User Processes by ID

7. To select a user’s processes by effective user ID (EUID) or name, use the -u option.
$ ps -fu tecmint
OR
$ ps -fu 1000

Print All Processes Running as Root (Real and Effecitve ID)

8. The command below enables you to view every process running with root user privileges (real & effective ID) in user format.
$ ps -U root -u root

Display Root User Running Processes

Display Group Processes

9. If you want to list all processes owned by a certain group (real group ID (RGID) or name), type.
$ ps -fG apache
OR
$ ps -fG 48

Display Group Processes

10. To list all processes owned by effective group name (or session), type.
$ ps -fg apache

Display Processes by PID and PPID

11. You can list processes by PID as follows.
$ ps -fp 1178

List Processes by PID

12. To select process by PPID, type.
$ ps -f --ppid 1154

List Process by PPID

13. Make selection using PID list.
$ ps -fp 2226,1154,1146

List Processes by PIDs

Display Processes by TTY

14. To select processes by tty, use the -t flag as follows.
$ ps -t pst/0
$ ps -t pst/1
$ ps -ft tty1

List Processes by TTY

Print Process Tree

15. A process tree shows how processes on the system are linked to each other; processes whose parents have been killed are adopted by the init (or systemd).
$ ps -e --forest

List Process Tree

16. You can also print a process tree for a given process like this.
$ ps -f --forest -C sshd
OR
$ ps -ef --forest | grep -v grep | grep sshd

List Tree View of Process

Print Process Threads

17. To print all threads of a process, use the -H flag, this will show the LWP (light weight process) as well as NLWP (number of light weight process) columns.
$ ps -fL -C httpd

List Process Threads

Specify Custom Output Format

Using the -o or –format options, ps allows you to build user-defined output formats as shown below.

18. To list all format specifiers, include the L flag.
$ ps L

19. The command below allows you to view the PID, PPID, user name and command of a process.
$ ps -eo pid,ppid,user,cmd

List Processes with Names

20. Below is another example of a custom output format showing file system group, nice value, start time and elapsed time of a process.
$ ps -p 1154 -o pid,ppid,fgroup,ni,lstart,etime

List Process ID Information

21. To find a process name using its PID.
$ ps -p 1154 -o comm=

Find Process using PID

Display Parent and Child Processes

22. To select a specific process by its name, use the -C flag, this will also display all its child processes.
$ ps -C sshd

Find Parent Child Process

23. Find all PIDs of all instances of a process, useful when writing scripts that need to read PIDs from a std output or file.
$ ps -C httpd -o pid=

Find All Process PIDs

24. Check execution time of a process.
$ ps -eo comm,etime,user | grep httpd

The output below shows the HTTPD service has been running for 1 hours, 48 minutes and 17 seconds.

Find Process Uptime

Troubleshoot Linux System Performance

If your system isn’t working as it should be, for instance if it’s unusually slow, you can perform some system troubleshooting as follows.

26. Find top running processes by highest memory and CPU usage in Linux.
$ ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head
OR
$ ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%cpu | head

Find Top Running Processes

27. To kill an Linux processes/unresponsive applications or any process that is consuming high CPU time.

First, find the PID of the unresponsive process or application.
$ ps -A | grep -i stress

Then use the kill command to terminate it immediately.
$ kill -9 2583 2584

Find and Kill a Process

Print Security Information

28. Show security context (specifically for SELinux) like this.
$ ps -eM
OR
$ ps --context

Find SELinux Context

29. You can also display security information in user-defined format with this command.
$ ps -eo euser,ruser,suser,fuser,f,comm,label

List SELinux Context by Users

Perform Real-time Process Monitoring Using Watch Utility

30. Finally, since ps displays static information, you can employ the watch utility to perform real-time process monitoring with repetitive output, displayed after every second as in the command below (specify a custom ps command to achieve your objective).
$ watch -n 1 'ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head'