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Introduction to the Linux Command Line on Raspberry Pi OS

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Getting Started with the Command Line
Managing Files and Directories
Managing Software
System Monitoring and Management
Networking Basics
Scripting Basics
Working with Git (Optional Advanced Topic)
Final Project: Building a Simple Command Line Application
Resources and Next Steps

Managing Processes

Learn how to manage processes using commands like kill, killall, and how to work with background processes.

By Kevin McAleer,    3 Minutes

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Introduction

Processes are running instances of programs. Managing them is a key part of system administration. In this lesson, you’ll learn how to manage processes, including how to kill unresponsive processes and how to work with background processes.

Learning Objectives

  • Understand what a process ID (PID) is.
  • Kill processes using kill and killall.
  • Work with background and foreground processes.

Understanding Process IDs (PIDs)

Every running process has a unique identifier called a Process ID (PID). You can find the PID of a process using the ps or top commands:

    ps

This will display a list of running processes along with their PIDs.

    PID TTY          TIME CMD
    2783 pts/0    00:00:00 bash
    2794 pts/0    00:00:00 ps

To see more detailed information about the processes, you can use:

    ps aux

This will show more detailed information about the processes.

USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root           1  0.0  0.5 169136 11168 ?        Ss   Aug23   0:00 /sbin/init sp
root           2  0.0  0.0      0     0 ?        S    Aug23   0:00 [kthreadd]
root           3  0.0  0.0      0     0 ?        S    Aug23   0:00 [pool_workque
root           4  0.0  0.0      0     0 ?        I<   Aug23   0:00 [kworker/R-rc
root           5  0.0  0.0      0     0 ?        I<   Aug23   0:00 [kworker/R-rc
root           6  0.0  0.0      0     0 ?        I<   Aug23   0:00 [kworker/R-sl
root           7  0.0  0.0      0     0 ?        I<   Aug23   0:00 [kworker/R-ne
root          11  0.0  0.0      0     0 ?        I    Aug23   0:00 [kworker/u8:0

grep is a command used to search for text patterns. You can use it to filter the output of ps:

    ps aux | grep <process-name>

Notice the | symbol, which is a pipe that sends the output of ps aux to grep.

Killing Processes with kill and killall

kill: Sends a signal to a process to terminate it. You need the PID to use this command.

    kill <PID>

killall: Kills all processes with the specified name.

    killall <process-name>

Background and Foreground Processes

Background Processes: Run a command in the background by adding & at the end.

    long_running_command &

Foreground Processes: Bring a background process to the foreground using fg.

    fg

Pausing and Resuming: Pause a process with Ctrl + Z and resume it with bg for background or fg for foreground.

Summary

In this lesson, you learned how to manage processes by identifying PIDs, killing unresponsive processes, and working with background and foreground processes. Effective process management is crucial for maintaining system stability.

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