Linux Process Management for Beginners - Complete Guide 2025

 

Introduction

Managing processes in Linux is one of the core skills that every user should learn, whether you are new to the system or already familiar with the basic commands.  Process management allows you to understand how your system runs the programs, handles multitasking and uses the system resources efficiently.

Process management is used in monitoring, controlling, and optimizing the active programs and background services that are running on your Linux system. With tools such as ps, top, htop, kill, and nice, you can easily monitor the system performance, terminate the unresponsive applications, adjust the process priorities, and troubleshoot the system performance issues in real time.

This guide will help system administrators, DevOps engineers and end users to understand the process management in Linux, process types and how to manage them efficiently. 

What is a Process in Linux?

Any running program or an instance of a running program is referred to as a process in Linux. When you launch an application, run a script or execute any command then the Linux kernel creates a new process to manage that execution.

Types of Processes in Linux

1. Foreground and Background Processes in Linux

Every program that you run or any command that you execute in the terminal is considered as a process in Linux. These processes can either run in the background or foreground, depending on how you start or control them. Understanding of this concept is very important for multitasking and efficient system management.

Foreground Process in Linux

A foreground process runs directly, interacts with the user and occupies the terminal until the task is completed. The terminal cannot be used for any other task or command until the running foreground process is finished or stopped.

In this example, a ping command is running in the foreground and you cannot execute any other command in the terminal until you stop it.

Key Point of Foreground Process

·         Keeps control of the terminal until it finishes

·         Requires direct input/output from the user

·         Must be finished or terminated before running another command

Background Process in Linux

A background process runs independently without occupying the terminal and allows you to continue using the same terminal for other tasks. You can send the process to the background by adding the ampersand (&) at end of the command.                                                                            

As you can see, vim command is running in the background. You will just get the process ID (PID) and your terminal will be immediately available for other commands.

Key Point of Background Process

·         Does not block the terminal

·         Ideal for resource-intensive or long-running processes

·         Can be managed using job control commands (jobs, fg, bg) 

Managing Foreground and Background Processes

You can control these processes using the following commands

Command                                          Description

Jobs                                                    Lists all running background jobs

Fg %job_id                                        Brings background jobs to foreground

Bg %job_id                                       resumes a stopped job in the background

Ctrl + Z                                             suspends a foreground process

Kill %job_id                                     terminates a background job

Commands with Examples

1. Jobs

2. fg %job_id

3. bg %job_id

4. kill %job_id

Why This Matters

·         Foreground processes are useful for interactive programs

·         Background processes help multitask efficiently on the same terminal

·         Understanding process control improves productivity and system management

2. Parent and Child Process in Linux

Every process originates from another process, just like a family tree. The process that creates another process is called a parent process and the new process initiated by the parent process is called a child process. Understanding this fundamental concept is important for system administrators and developers as it helps to grasp how your system handles multitasking and controls the processes.

What is Parent Process in Linux?

A parent process is a process that can create one or more new processes. It initiates another process using a system call like fork () or a command executed from the shell.

When you open a terminal such as bash, it runs as a process and you execute any command in that terminal, then bash becomes a parent process and the command becomes the child process.

Opening the terminal is a parent process                                                                   

Executing the command 'll' in the terminal is a child process.

What is a Child Process in Linux?

A child process is a process that is created by a parent process using the fork () system call or by executing any command. It inherits some characteristics from the parent process, such as environment variables, file descriptors and user ID but it has a unique process id (PID).

On exit or termination of the child process SIGCHLD signal is sent to the parent process to inform about the termination or interruption of the child process.

How the Parent and Child Process Work Together

·         When the parent process creates a child process with the fork () system call then

·         Parent process duplicates itself

·         The child process gets a new PID but shares the same code and environment initially

·         Both parent and child run independently

·         When the child finishes, it sends a termination signal to the parent process

·         The init or systemd process (PID 1) is the parent of all processes

·         If the parent process terminates before the child process, then the child is adopted by init

View Parent and Child Processes

1. Using ps -ef

It lists all processes along with PPID (Parent Process ID) and PID (Process ID)

2. Using pstree

This command visually displays processes in a tree-like structure, showing parent-child relationships clearly.

3. Using ps -ejH

This displays a hierarchical process list in the terminal.

3. Orphan and Zombie Processes

Orphan Process

If a parent process terminates before the child process, then the child process becomes an orphan and is adopted by init or systemd.

Zombie Process

A zombie process occurs when a child process finishes execution but its parent has not yet read its status, then it remains in the process table with “Z” state.

You can check the zombie process with ps aux | grep Z command.                                                     

Summary Table

Term	Description	Example
Parent Process	creates another process	bash, starting ls
Child Process	created by parent process	ls command
Orphan Process	The parent terminated before the child	adopted by init
Zombie Process	A completed child not reaped by the parent	ps aux

Why It Matters

Understanding parent and child processes is vital for

·         Debugging process trees

·         Managing system performance

·         Prevent orphan or zombie processes

Linux Process States

Every process goes through different states in its lifecycle in Linux. Understanding these states helps system administrators and developers diagnose system performance, manage task effectively and troubleshoot issues.

Running (R)

Sleeping (S)

Stopped (T)

Zombie (Z)

1. Running (R)

A process in this state is actively using the CPU or ready to run and waiting for the scheduler to allocate a CPU. This is the most active of processes. Seen as “R” in top or ps.

2. Sleeping (S)

A process is inactive and waiting for an event or resource. There is two types of sleeping processes.

Interrupted Sleep

Uninterrupted Sleep

Interrupted Sleep (S) awakened by signals, e.g., waiting for I/O.

Uninterrupted Sleep (D) cannot be interrupted, typically waiting for hardware response.

Mostly, the process spends time here. Seen as S or D in the top.

#ps -eo, pid, state, cmd

3. Stopped (T)

A process enters in stopped state when it receives a SIGSTOP or SIGTSTP signal. Its execution is suspended and it will only resume on receiving a SIGCONT signal or be terminated by SIGKILL. It can be stopped using Ctrl + Z in the terminal and seen as T in top or ps.

4. Zombie (Z)

A process goes in zombie states when a child process terminates but its parent process has not called wait or waitpid () to collect its exit status. The zombie process is dead but its entry in the process table remains until reaped by the parent. Seen as “Z” in top or ps and consumes no CPU or memory.

Process State Table

State	Symbol	Description	Command
Running	R	Actively using CPU or waiting to run	ps -eo pid, state,cmd
Sleeping	S/D	waiting for an event or I/O	ps -eo pid, state, cmd
Sopped	T	suspended or paused	ps -eo pid, state, cmd
Zombie	Z	process finished, but not reaped	ps aux

How Linux Manages the Processes

Role of Linux kernel and Process ID (PID)

The kernel is the core part of the operating system, responsible for managing all processes, hardware resources, and system operations. It is a bridge between hardware and software, ensuring that every process gets the CPU, memory, and I/O resources they need to run effectively.

When a new process is created, the kernel assigns it a unique process ID (PID), a numerical identifier that is used to track and manage the process throughout its lifecycle. Every process, whether it’s a system daemon, a user application or a background service, has its own PID.

Key Points about Kernel and PID

·         The kernel controls process creation, scheduling and termination. It ensures that system resources are allocated fairly and efficiently.

·         Every process has a unique PID, making it easy to monitor or control specific tasks using commands such as ps, top and kill.

·         When one process creates another, the new process (child) inherits attributes from its creator (parent). The parent process ID (PPID) can be viewed alongside the PID.

·         The kernel manages and updates the states of each process running, sleeping or zombie based on system events and user commands.

Command Examples

·         Ps -ef displays all running processes with their PID and parent PID.

·         Pidof process_name shows the PID of a specific process

·         Kill PID terminates a process using its PID  

Viewing Active Processes with ps in Linux

One of the most commonly used commands for monitoring running processes is the ps (Process Status) command. It provides detailed information about active processes, including their PID (Process ID), PPID (Parent Process ID), CPU usage, memory usage and execution state. Understanding how to use the ps command is a fundamental skill for any Linux administrator or beginner learning process management.

The ps command reads data directly from the kernel and displays it in a human-readable format, making it useful for quick system checks and diagnoses.

1. Basic Syntax

ps [options]

By default, running ps without any options displays processes associated with the current terminal session.

Here:

·         PID – Process ID (unique identifier for each process)

·         TTY – the terminal associated with the process

·         TIME – CPU time used by the process

·         CMD – Command that started the process

1. View All Running Processes (system-wide)

#ps –e

Or

#ps –A

Shows every process currently running on the system.

2. Full Format List

Displays more details, including PPID, start time and command arguments.

# ps -f

3. View All Processes with User Information

This is the more common and informative form.

#ps -ef

It shows all system processes with details like

UID – User ID of the process owner

PID – Process ID

PPID – Parent Process ID

C – CPU utilization

STIME – Start time of the process

CMD – Command used to start the process

4. View Processes by Users

Displays all processes running under a specific user account.

#ps -u testuser

5. Display Hierarchical Tree View

This shows the process tree revealing the parent-child relationship between processes.

#ps axjf

6. Combine ps with grep to Filter Output

This filters the process list to show only entries matching the keyword “gitlab”. It is a quick way to check if a service or process is running. 

#ps -ef | grep gitlab

Practical Use Cases

·         Check if a particular service is running

·         Identify which user started a process

·         Find the PID of a process to stop or monitor it

·         Examine a process hierarchy for debugging

Pro Tip

Combine ps with other commands, such as grep, awk, or sort, for advanced filtering.

The ps command is your gateway to understanding the behavior of processes in Linux. Whether you are analyzing performance, troubleshooting a system or just exploring, mastering PS gives you deeper control of your system.

Viewing Processes in Real Time with the top Command

The top command is the most commonly used and powerful utility in Linux for real-time process monitoring. It provides a continuous, updated view of system performance, including CPU usage, memory consumption, running tasks, and process ID (PID).

When you run top it retrieves data directly from /proc file system, which contains runtime system information such as process details, CPU statistics and memory usage. The display refreshes after every few seconds and gives a current overview of system activity to the administrators.

Basic Usage

#top

Key Section

PID: Unique process ID assigned by the kernel

USER: The owner of the process

%CPU / %MEM: Percentage of CPU and memory usage

TIME+: Total CPU time the process has consumed

Command: The name of the running process or command

Interactive Keys

q – Quit top

k – Kill a process (you’ll be prompted for process ID)

r – Change process priority (renice)

h – Display help

·       Helps identify CPU-intensive processes

·       Detects memory leaks or runaway processes

·       Useful for performance troubleshooting on production servers

Stopping and Killing Processes in Linux (kill, pkill, killall)

Sometimes a process may hang, consume too many resources or behave unexpectedly. In such situations, you may need to stop or terminate the process manually. Linux offers several commands for this purpose, such as kill, pkill, and killall, each offering a different level of control.

1.  Using the kill command

The kill command sends a signal to the process ID (PID) to stop or terminate it. You can view the PID of a running process using ps or top command.

#kill PID

#kill 813004                         #sends SIGTERM to (default signal) to process 813004

#kill -9 813004                    #forcefully kills the process using SIGKILL

Common Signals

SIGTERM (15): Gracefully stops a process, allowing cleanup

SIGKILL (9): Immediately kills the process, cannot be ignored

SIGHUP (1): Restarts the process (useful for daemons)

2. Using the pkill Command

The pkill command allows you to terminate processes by name instead of PID. It is especially useful when you have multiple instances of the same program.                                                                  

This command will stop all processes named vim.

3. Using the killall Command

The killall command terminates all processes that share the same name, similar to pkill but with broader reach across the sessions.                                                                                  

This will stop all vim instances running on the system.

Nice

Process priority determines how much CPU time a process receives as compared to other processes. Adjusting priority helps manage system performance by allocating more CPU time to critical tasks and prioritizing less important ones. This is done using nice and renice commands.

What is Nice Value?

The nice value ranges from -20 (highest priority) to +19 (lowest priority). By default, more processes start with a nice value of 0. Only the root user can assign a negative nice value (higher priority).

Using nice Command (Set Priority When Starting Process)

You can start a process with a specific nice value.

#nice –n 10 vim&

This runs with a lower priority (nice value 10).

Using the renice Command (Change Priority of Running Process)

#sudo renice –n 5 -p 963021

View Priority and Nice Values

You can see nice and priority values in the top. In the top, look for column NI (nice) and PR (priority).

Practical Use Cases

·         Run system updates in the background

·         Give critical backup scripts a higher CPU priority

·         Adjust heavy background processes

Important Notes

·         Higher nice value – lower priority (less CPU)

·         Lower nice value – higher priority (more CPU)

·         Root privileges are required for negative nice values

·         Always monitor system load before changing priorities

Troubleshooting Common Process Issues in Linux

Every administrator encounters process-related issues on Linux system. Troubleshooting these issues efficiently requires understanding how to identify misbehaving processes, analyze system resources and take corrective action.

1. High CPU Usage

Symptoms: the system feels bulky, fans run constantly or processes consume too much CPU time.

Commands to Diagnose

·         Top – to see which process is consuming CPU

·         ps –eo, pid, ppid, cmd, %mem, %cpu lists top CPU consumers

Fix

If a process is stuck in a loop, restart or terminate it with the command.

#sudo kill -9 (PID)

2. Zombie Process

Symptoms: Processes remain visible with status Z (zombie).

Command to Diagnose

#ps aux | grep Z

Cause: parent process didn’t read the child’s exit status.

Fix

Restart the parent process or service managing the zombie. If it doesn’t work, a system reboot clears them.

3. Stuck or Unresponsive Processes

Symptoms: Process not responding to input or taking too long to finish.

Command to Diagnose

#ps –eo, pid, stat, cmd | grep D

(D state=uninterruptable sleep, often I/O related).

Fix

Check for I/O wait using dmesg. If a process is waiting for hardware, resolve the device issue or unmount affected drives.

4. Runaway Background Jobs

Symptoms: Background tasks consume excessive system resources.

Command to Diagnose

#jobs –l

#ps –ef | grep username

Fix

Bring the job to the foreground with fg and stop it or kill it.

#kill %job_ID

5. Scheduling and Priority Issues

Symptoms: High-priority processes require more resources, delaying others.

Commands to Diagnose

#ps –eo, pid, ni, cmd

Fix

Adjust process priority

#sudo renice <new_value> -p PID

Best Practices for Process Management

·         Avoid killing critical system processes

·         Regularly monitor CPU and memory usage

·         Use automation for recurring tasks

·         Practice the least privilege principle when using sudo

Frequently Asked Questions (FAQ)

1. What is Process Management in Linux?

Process management in Linux is refers to the handling of system processes, starting, monitoring, prioritizing, stopping or killing them.

2. What is Process ID (PID)

Every process in Linux is assigned a unique process ID (PID) by the kernel. This ID helps in identifying and managing processes using commands such as ps, kill, or top.

3. What is the role of the kernel in Process Management?

The kernel is responsible for creating, scheduling and managing processes. It assigns PID and handles context switching. It ensures each process gets fair access to system resources like CPU and memory.

4. What is a zombie process and should I be worried?

A zombie process is a terminated process that has not been cleaned up by its parents. A buildup of zombie processes indicates that a parent process is not managing its child process properly.

5. Why is process management important in Linux?

The process management ensures optimal performance, prevents system overload and enhances security.

Conclusion

One of the most vital skills that one can have, regardless of whether he is a beginner and venturing into the world of Linux or an expert administrator dealing with production servers, is process management in Linux.

This guide has made you visualize an active process, performance of a diagnostic system, prioritization with nice and renice, and an unresponsive process, which is ended through tools such as ps, top, and htop. You have also heard of the functionality of processes behind the scenes in the Linux kernel, how processes are allocated PIDs (Process IDs) and how the system gets to be steady and stable with good scheduling.

Process management enables you to have full control over your system. By following the orders and the good practices that are presented in this guide, you will be able to learn more about the way in which Linux manages to cope with multitasking and resource distribution.

No matter how you use Linux, be it with background service management, performance troubleshooting, or just to view the inner workings of Linux, having command over processes provides you with the skills and ability to deal with any condition of a system.

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