Beginners Guide for PS Command in Linux

The PS, a.k.a. “process status”, is a native command-line utility for UNIX-based systems to monitor the currently running processes in your system.

It reads the information from the virtual files in the /proc filesystem and gives the running processes information like memory consumption, CPU usage, PID, command name, etc.

The output of this command varies depending on the running processes and the parameter used to view the list of processes.

Tutorial Details

Syntax of the PS Command

The ps command takes only one argument as an option.

$ ps [OPTION]

It will list the running processes in your current shell without any arguments.

$ ps

Output:

Note that you always see the ps process in the output when you execute this command, as ps is also a process.

The PS command output column breakdown is as follows:

The PS command supports three types of syntax styles:

In Linux, every process has several IDs associated with it that you must know before understanding the PS command.

The PGID (Process Group) and SID (Session ID) are ways to manage multiple related processes as a unit.

A group of multiple process groups might belong to the same session, and the same session might hold multiple process groups.

Listing All Running Processes in Your System

The “-A” or “-e” flag will list all the running processes in your Linux system in generic (Unix/Linux) format.

$ ps -A

Output:

Execute the following command to list all the active processes in BSD format:

$ ps aux

Output:

List only the specific process that matches a string used as an argument to the grep command.

$ ps aux | grep nginx

Output:

Use the “--no-header” flag to list the running process without a header.

$ ps --no-header

Output:

Listing the Processes Not Associated with the Terminal

The “-a” flag will display all the running processes except for the session leaders and processes that are not associated with a terminal.

$ ps -a

Output:

Listing All Processes Except Session Leaders

The “-d” flag will list all the running processes except for the session leader processes.

$ ps -d

Output:

Listing All Processes with Full-Format Listings

The “-f” or “-F” flag can be combined with other options to add additional columns like “UID” or “PPID“.

$ ps -af

Output:

Listing All Processes Except Those That Fulfill the Specified Conditions (Negates the Selection)

Using the “-N” or “--deselect” flag will list all the processes except those that are fulfilled by the specified conditions (the opposite of selection).

For example, if you specify “-a” with “-N“, it will show you the opposite result that only includes the processes with both session leaders and processes not associated with a terminal.

$ ps -a -N

Output:

Listing All Processes Associated With the Current Terminal

The “t” or “T” flag will list all the processes associated with your current terminal.

$ ps t

Output:

Listing Only the Processes Owned by You

The “x” or “-x” flag will only list the processes owned by the current logged-in user.

$ ps x

Output:

Listing Processes by Real or Effective User ID

Use the “-U” flag to list the processes based on real user ID (RUID) or name, or use the “-u” flag to list the processes based on effective user ID (EUID) or name, along with the “-f” flag to print the additional columns.

$ ps -fU linuxtldr

Output:

Or

$ ps -fu 1003

Output:

Listing All Processes Running as Root

The following command will list all the processes running as root in real or effective user format.

$ ps -U root -u root

Output:

Listing the Group of Processes (Real or Effective Group ID)

Execute the following command to get the list of processes owned by a specific group (real group ID or name).

$ ps -fG root

Output:

Execute the following command to list the processes owned by the effective group name (or session).

$ ps -fg root

Output:

Displaying Specific Process Information with PID or PPID

The following command will list the information for the specified process PID.

$ ps -fp 4995

Output:

Use the following command to specify PPID.

$ ps -f --ppid 1

Output:

Listing the Processes Based on TTY

Use the “-t” flag to list the processes based on tty.

$ ps -f -t pts/0

Output:

Or

$ ps -f -t tty2

Output:

ASCII Art Process Tree

Use the “--forest” flag to display the list of processes linked to each other in ASCII art.

$ ps -e --forest

Output:

Grep the name of the process to print the specific process tree.

$ ps -e --forest | grep gnome-terminal

Output:

Listing the Processes with Custom Output Format

Execute the following command with “L” to get the list of valid format specifiers.

$ ps L

Output:

Use the “-o” or “--format” flag to list the running process in the above format.

The following command will list the running processes with their PID, PPID, username, group, and command.

$  ps -eo pid,ppid,user,group,cmd

Output:

Listing Parent and Child Processes

Use the “-C” flag to list all the processes with the specified command name, including its child processes.

$ ps -C nginx

Output:

That was the end of the PS command examples.

This command is very useful.

If any examples are missed that must be included in this article, let us know in the comment section.