Process is the application or software that is currently running. Each process is identified by unique ID called process ID. Processes can create other processes called child or sub processes. There are different tools to look at the processes running including child processees. Processes and resources required by the process are managed by operating system kernel

This article will walk you through the ways to view the process tree using different commands such as

• ps
• tree
• pstree

PS command

The command “ps” is the intrinsic part of every Linux distribution. To display all processes using ps command

ps -waxf 

To display process tree use the command line option “–tree”

To display all processes running use the option “-A” or “-e”

# ps -A

Filter Processes by TTY

Display process associated with TTY

ps a

Display processes that are not associated with TTY

ps -a 

Display Process by User

To display processes owned by the current user

ps x

To display processes running with respect to user

ps u 

To filter the processes by the user selected use the option -U or –User

ps -U user  #name or id

or,

ps --User user # name or id

List Processes by Parent

To list all subprocess by parent process ID

ps --ppid parent_process_id

Process Tree by PS

To display the ASCII tree of all processes with subprocesses use the option “f” or “–forest”

ps --forest 

Tree command

Do you know, proc file system contains process ID as directories and each directory contains the comprehensive information about that corresponding process including executable path. Such that we can use the traditional tree command to display the process tree

tree /proc 

To display only the directories

tree -d /proc 

PSTree

Even though traditional “ps” command works well. We have the specific utility which does this single job very well, that is “pstree” command. While “ps” command some what spits out the different kind of output at times compared to Linux counter parts. This command pstree is quite helpful to print process tree on Mac

Install the command pstree

sudo apt install psmisc

Install pstree on Mac

brew install pstree 

To display the process tree using pstree command

pstree 

To include the processes related to process ID (PID) in the output of pstree command

pstree -p pid

Usage of command pstree

Usage: pstree [-f file] [-g n] [-l n] [-u user] [-U] [-s string] [-p pid] [-w] [pid ...]
   -f file   read input from <file> (- is stdin) instead of running
             "ps -axwwo user,pid,ppid,pgid,command"
   -g n      use graphics chars for tree. n=1: IBM-850, n=2: VT100, n=3: UTF-8
   -l n      print tree to n level deep
   -u user   show only branches containing processes of <user>
   -U        don't show branches containing only root processes
   -s string show only branches containing process with <string> in commandline
   -p pid    show only branches containing process <pid>
   -w        wide output, not truncated to window width
   pid ...   process ids to start from, default is 1 (probably init)

Other command line tools are available on Linux presenting GUI using ncurses. Which are used for monitoring and process management such as

1. atop
2. vtop
3. htop
4. btop++
5. nmon
6. Glances