How to control background jobs?

Controlling Background Jobs in Linux

In the Linux operating system, background jobs refer to processes that run in the background without requiring user interaction. These jobs can be started, paused, resumed, and terminated using various commands and techniques. Mastering the control of background jobs is an essential skill for Linux users and administrators, as it allows them to manage system resources more efficiently and automate repetitive tasks.

Understanding Background Jobs

In a Linux system, when a user runs a command, the process can be executed in the foreground or the background. Foreground processes require user interaction and occupy the terminal session, while background processes run independently without blocking the terminal.

To illustrate the concept, imagine you're working on a document in a text editor (a foreground process) and you need to run a long-running task, such as compiling a large codebase. Instead of waiting for the compilation to finish before you can continue editing your document, you can send the compilation task to the background, allowing you to continue working on the document in the foreground.

graph LR A[User] --> B[Foreground Process] A --> C[Background Process] B --> D[Occupies Terminal] C --> E[Runs Independently]

Launching Background Jobs

To start a process in the background, you can append the & symbol to the command. This tells the shell to execute the command in the background and return control to the user immediately.

# Example: Running a long-running task in the background
$ sleep 60 &
[1] 12345

In the example above, the sleep 60 command runs in the background, and the shell returns the job number (in this case, [1]) and the process ID (in this case, 12345) to the user.

Listing and Controlling Background Jobs

Once you have started a background job, you can use the following commands to manage it:

jobs: This command lists all the background jobs currently running in the shell.

$ jobs
[1]  Running    sleep 60 &
[2]- Running    sleep 120 &
[3]+ Running    sleep 180 &

fg: This command brings a background job to the foreground, allowing you to interact with it directly.

$ fg %2
sleep 120

bg: This command resumes a suspended background job.

$ sleep 60 &
[1] 12345
$ kill -STOP 12345  # Suspend the job
$ bg %1            # Resume the job in the background
[1] 12345

kill: This command can be used to terminate a background job.

$ kill %2  # Terminate the job with job number 2
$ kill 12345  # Terminate the job with process ID 12345

Advanced Techniques

Redirecting Output: You can redirect the output of a background job to a file to avoid cluttering the terminal.

$ command > output.txt &

Nohup: The nohup command allows you to run a process that continues to run even after you log out of the system.

$ nohup command &

Screen and tmux: These terminal multiplexers provide advanced features for managing background jobs, including the ability to detach and reattach sessions, split the screen, and more.

graph TD A[User] --> B[Foreground Process] A --> C[Background Process] B --> D[Occupies Terminal] C --> E[Runs Independently] C --> F[Redirected Output] C --> G[Nohup] C --> H[Screen/tmux]

By understanding and effectively using these techniques, you can streamline your workflow, automate repetitive tasks, and better manage system resources in a Linux environment.