Linux Job Foregrounding

Introduction

In Linux operating systems, multitasking is an essential capability that allows users to run multiple processes simultaneously. One powerful feature of Linux terminals is job control - the ability to manage processes by running them in the background and bringing them to the foreground when needed.

This lab introduces you to Linux job control, specifically focusing on the process of foregrounding background tasks. You will learn how to start tasks in the background, list running jobs, and bring specific tasks to the foreground using the fg command. These skills are valuable for enhancing productivity when working with long-running operations in a Linux environment.

Skills Graph

Creating and Running Background Tasks

In this step, you will learn how to create a script that simulates a long-running task and run it in the background.

Understanding Foreground vs Background Processes

In a Linux terminal, processes can run in either the foreground or background:

• Foreground process: When a command runs in the foreground, it occupies your terminal until it completes. You cannot run other commands until it finishes.
• Background process: When a command runs in the background, it executes "behind the scenes" while your terminal remains free for other tasks.

Let's start by navigating to the project directory:

cd ~/project

Now, let's create a simple script that simulates a long-running task. We'll use this to demonstrate background and foreground operations:

nano long_running_task.sh

In the nano editor, enter the following code:

#!/bin/bash
echo "Starting a long task..."
sleep 60 ## This will pause for 60 seconds
echo "Task completed."

To save the file, press Ctrl+O followed by Enter, and then Ctrl+X to exit nano.

Next, make the script executable with the following command:

chmod +x long_running_task.sh

Let's run this script in the background by adding an ampersand (&) at the end of the command:

./long_running_task.sh &

You should see output similar to this:

[1] 1234
Starting a long task...

The number in square brackets [1] is the job number, and the number after it (in this example, 1234) is the process ID. Your terminal is now free for you to enter other commands while the script continues running in the background.

Managing Multiple Background Jobs

In this step, you will learn how to start multiple background tasks and check their status.

First, let's start another instance of our script in the background:

./long_running_task.sh &

You should see another job number and process ID displayed, along with the "Starting a long task..." message.

Checking Background Jobs

To see a list of all jobs running in the background, use the jobs command:

jobs

The output should look similar to this:

[1]-  Running                 ./long_running_task.sh &
[2]+  Running                 ./long_running_task.sh &

This shows:

• Job numbers in square brackets [1] and [2]
• The status of each job (Running)
• The command that was executed
• The + symbol indicates the "current" job (most recently started or used)
• The - symbol indicates the job that would become current if the current job completed

Let's start a third background job:

./long_running_task.sh &

Check the jobs list again:

jobs

You should now see three running jobs in the list.

Bringing Jobs to the Foreground

In this step, you will learn how to bring background jobs to the foreground using the fg command.

Using the fg Command

The fg command brings a background job to the foreground, making it the active process in your terminal. When a job is in the foreground, it can receive input from the keyboard, and its output is displayed directly in the terminal.

To bring the most recent background job (marked with + in the jobs output) to the foreground, simply type:

fg

You should see the command running in the foreground, and your terminal will be occupied until the command completes. The output will look like this:

./long_running_task.sh

And if the task is still running, you'll have to wait for it to complete. When it finishes, you'll see:

Task completed.

If you need to interrupt a foreground process before it completes, press Ctrl+C.

Let's start another background job:

./long_running_task.sh &

Now check the jobs list:

jobs

Foregrounding a Specific Job

In this step, you will learn how to bring a specific background job to the foreground using its job number.

Using fg with Job Numbers

When you have multiple background jobs, you can bring a specific job to the foreground by referencing its job number with the fg command.

First, let's make sure we have multiple jobs running. Start a couple of new background tasks:

./long_running_task.sh &
./long_running_task.sh &

Check the list of jobs and their numbers:

jobs

To bring a specific job to the foreground, use the format fg %jobnumber. For example, to bring job number 1 to the foreground:

fg %1

The output will show the command running in the foreground:

./long_running_task.sh

Wait for the task to complete or press Ctrl+C to interrupt it.

Now try bringing another job to the foreground. For example, if you have a job with number 2:

fg %2

This technique is useful when you need to switch between multiple tasks, giving attention to a specific process as needed.

Summary

In this lab, you have learned essential skills for managing processes in a Linux environment:

1. Creating and executing background tasks: You created a script that simulates a long-running operation and learned how to run it in the background using the & symbol.

2. Managing multiple background jobs: You learned how to start multiple background tasks and check their status using the jobs command.

3. Bringing jobs to the foreground: You discovered how to use the fg command to bring background tasks into the foreground, either the most recent job or a specific job by referencing its job number.

These job control techniques are fundamental for efficient multitasking in Linux. They allow you to:

• Run time-consuming processes without tying up your terminal
• Monitor multiple operations simultaneously
• Switch between tasks as needed
• Manage your workflow more effectively

As you continue working with Linux systems, these commands will become valuable tools in your daily operations, especially when working with servers, running scripts, or managing multiple processes.