Difference between revisions of "Linux-Ubuntu/C2/Working-with-Linux-Processes/English"

Title Slide

Learning Objectives

• Processes in Linux
• Parent and child processes
• Process creation and termination
• Process attributes like PID and PPID
• The ps command and its options

System Requirements

Ubuntu OS version 24 point zero 4 

Pre-requisites

https://EduPyramids.org

Learners should have Ubuntu version 24 point zero 4.

For the prerequisite Linux tutorials please visit this website.

Code Files

The following code file is required to practice this tutorial

1. wlp-commands.txt

This file is provided in the Code Files link of this tutorial page.

This file is provided in the Code Files link of this tutorial page.

What is a Process ?

processing.png

The shell that accepts commands is a process.

Commands typed in the terminal become processes when executed.

For example, video players, web browsers, and running shell scripts are also processes.

What is a Shell?

Shell1.png

It runs commands and shows output.

The kernel starts the shell at login.

The shell creates processes for terminal commands.

Press Ctrl + Alt + T keys.

Displaying this prompt is the job of the shell process.

Highlight Date.

Highlight Output.

As soon as we do this, the shell process creates a new process called date.

The shell creates the date process, so it is called the parent process.

The date is called its child process.

After displaying the system date and time, the date process ends.

Spawning

Starting a new process is called spawning a process.

We can call this child shell as a subshell, or shell two.

We see a list of files and directories as output.

At this moment, a new process named ls is created.

Shell 1 is the grandparent of the l s process.

The l s process is the child of Shell 2.

At the same time, Shell 2 is the child of Shell 1.

This terminates Shell 2, returning us to the original command prompt of Shell 1.

PID and PPID

parent-child.png

The key process attributes are P I D (Process ID) and P P I D (Parent Process ID).

These details are stored by the Linux kernel in the process table.

PID (Process ID) is a unique number assigned to each process by the kernel.

PPID (Parent Process ID) is the PID of the process that created (spawned) it.

press Enter

point mouse to output PID number.

A number is displayed.

This number is the PID of the current shell.

It shows the processes currently running.

A list of all the processes owned by the current user.

hover mouse over PID column

hover mouse over TTY column

hover mouse over TIME columnHighlight previous commands output PID number

Name of the process under the C M D column.

P I D of the process.

TTY shows the terminal or console linked to the process.

TIME shows the total CPU time used by the process.

The P I D of the shell matches the number shown by echo dollar dollar command.

• bash, which is the shell itself, and
• ps, the command we just ran.

Type s h and press Enter.

Highlight bash, sh, ps highlight all the PID number.

We can now see three processes:

• bash the original shell
• s h the subshell we just spawned
• p s the command itself

Notice that the bash PID remains the same.The p s command has many options.

Show the output Highlight bash, sh, and ps -f.

This lists three processes again: bash, s h, and p s hyphen f.

• U I D shows the user who started the process.
• P P I D shows the P I D of the parent process.

Therefore, the P I D of bash is the same as the P P I D of s h.

Highlight C column,

The PID of s h matches the P P I D of p s in the p s hyphen f output.

The C column shows the CPU usage percentage over the process lifetime.

In this example, it is 0 due to minimal CPU usage.

The other fields are the same as those displayed earlier by p s.

Linux Processes

process.png

1. User processes – These are started by users.

For example, p s or most commands we run in the terminal.

1. System processes – These are started by the system, often during system startup or user login.

For example, bash is a system process.

Press enter

and press Enter.

We can see a large list of processes.

ps -e | more

press Enter

and press Enter.

Press Enter and scroll through the rest of the process list.The first process in this list is particularly interesting.

It is called the init process.

Almost all other processes are spawned from init, and it always has a P I D of 1.

Type exit

Press Enter

Highlight the original prompt

Type exit and press Enter to leave the shell and return to the original prompt.

Summary

In this tutorial, we have learnt about:

• Processes in Linux
• Parent and child processes
• Process creation and termination
• Process attributes like PID and PPID
• The ps command and its options

Let us summarise.

As an assignment,

Run the following commands and check the output.

ps -ef

ps -eF

ps -ely

ps -c

Thank you

Thank you.