Process Management In Linux Commands With Examples

Process Management in Linux

In Linux and UNIX-based operating systems, one of the most crucial ideas is process management. Whether you’re running a command at the terminal, playing a movie, or launching a browser, every action you take on a Linux system takes the form of a process. You can effectively manage system resources, solve issues, and monitor system performance by having a solid understanding of how processes operate.

What is process in Linux?

A process is an instance of a program that is running on the system at the moment.

Program: A static file sitting on your disk (e.g., /bin/bash).
Process: That file loaded into memory and actively running.

As an example:

firefox becomes a process when you enter firefox in the terminal.
If you type ls, the command will execute as a temporary process.

Each process has:

Its own memory space
A unique ID (PID)
A priority level
A state (running, sleeping, etc.)

Linux multitasks, allowing thousands of processes to run simultaneously.

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Processes States

Each process in Linux has a state that indicates what it is doing at the moment.

Running (R)

The CPU is being used actively by the process.
As an example:
- Playing a video in a video player.

Sleeping (S)

The process is waiting on something, such as disk data or human input.
As an example:
- An open browser awaiting your click on a link.

Uninterruptible Sleep (D)

It is unable to be stopped while it waits for hardware input.
As an example:
- A process that is awaiting a disk read.

Stopped (T)

The procedure is now on hold.
As an example:
- On an active program, pressing Ctrl + Z.

Zombie (Z)

Even though the process has completed running, its memory entry is still present.
As an example:
- An exiting child process whose status has not been retrieved by the parent.
Despite not using CPU, zombie processes are a sign of inadequate program cleanup.
Processes don’t just “run”; they move through different states based on what the CPU is doing.

Code	State	What it means
R	Running / Runnable	Actively using the CPU or waiting in line to use it.
S	Sleeping	Waiting for something to happen (like a keystroke or a file to load).
D	Uninterruptible Sleep	Waiting for hardware (usually a disk). It cannot be killed until the hardware responds.
T	Stopped / Traced	Paused by the user or a debugger.
Z	Zombie (Defunct)	A process that finished but its parent hasn’t acknowledged it yet. It uses no RAM but stays in the process table.

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Process commands in linux with examples

Linux provides multiple commands to view and monitor processes.

ps – Process Snapshot

The ps command shows a snapshot of currently running processes.

Basic Usage

bash

ps

Shows processes running in the current terminal.

Common Options

bash

ps -ef

Shows:

All processes
User who started them
PID
Parent PID
Start time

Example output:

bash

UID   PID  PPID  CMD
root  1    0     systemd
user  2345 1     firefox

top – Live Process Monitor

The top command shows real-time process activity.

bash

top

It displays:

CPU usage
Memory usage
Running processes
System load

You can:

Press q to quit
Press k to kill a process
Press M to sort by memory
Press P to sort by CPU

htop – Advanced Process Viewer

htop is an improved version of top with colors and mouse support.

bash

htop

Features:

Tree view of processes
Kill processes with keyboard
Easy sorting and filtering
Better visual display

It is not installed by default on all systems.

Install it using:

bash

sudo apt install htop
sudo pacman -S htop

pstree – Process Tree

pstree shows processes in a tree structure.

bash

pstree

This shows parent-child relationships.

Example:

bash

systemd
 ├─NetworkManager
 ├─sshd
 │   └─bash
 │       └─vim

This helps understand which process started which.

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Process IDs (PID)

Every process has a Process ID (PID).
The PID is a unique number assigned by the system.

Example:

bash

ps -ef | grep firefox

Output:

bash

user  2345  1  firefox

Here, 2345 is the PID of Firefox.

The system process always has:

bash

PID 1 = systemd or init

This is the first process started at boot.

Killing Processes

Sometimes processes freeze, crash, or consume too many resources. Linux allows you to manually stop them.

kill – Terminate a Process

The kill command sends a signal to a process.

bash

kill PID

Example:

bash

kill 2345

This sends a SIGTERM signal (polite request to exit).

kill -9 – Force Kill

If a process does not stop:

bash

kill -9 PID

This sends SIGKILL, which:

Immediately stops the process
Does not allow cleanup
Should be used only if necessary

Example:

bash

kill -9 2345

killall – Kill by Name

Instead of using PID:

bash

killall firefox

This kills all processes named “firefox”.

Be careful: It kills every instance.

Foreground and Background Processes

Linux allows running tasks in foreground or background.

Foreground Process

A process that runs directly in your terminal.

Example:

bash

ping google.com

It occupies the terminal until you stop it.

Background Process

A process that runs without blocking the terminal.

Example:

bash

ping google.com &

Now it runs in background.

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Jobs Command

View background jobs:

bash

jobs

Bring a job to foreground:

bash

fg %1

Send job to background:

bash

bg %1

Stop a foreground process:

bash

Ctrl + Z

Nice and Renice (Process Priority)

Linux uses priority levels to decide which process gets more CPU time.

Nice Value

Nice values range from:

-20 (highest priority)
+19 (lowest priority)

Default nice value:

bash

0

nice – Start Process with Priority

Example:

bash

nice -n 10 firefox

This starts Firefox with lower priority.

renice – Change Priority of Running Process

Example:

bash

renice -5 -p 2345

This increases priority of PID 2345.

Only root can assign negative values.

Real-Life Examples

Example 1: Kill a frozen browser

bash

ps -ef | grep chrome
kill -9 PID

Example 2: Run long task in background

bash

tar -cvf backup.tar folder/ &

Example 3: Lower priority for heavy task

bash

nice -n 15 ffmpeg -i video.mp4 output.mp4

This ensures your system stays responsive.

Summary Cheat Sheet

Task	Command
Find a PID	`pidof [name]` or `ps aux
Emergency Stop	`Ctrl + C` (Kill) or `Ctrl + Z` (Pause)
Check CPU/RAM	`htop`
Polite Kill	`kill [PID]`
Forced Kill	`kill -9 [PID]`
Boost Priority	`sudo renice -n -10 -p [PID]`

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Process Management In Linux Commands With Examples