Job Control (bg, fg, jobs)

Welcome to Job Control! This powerful feature in your Linux shell lets you manage running programs without closing your terminal or opening new ones.

Think of it as multitasking for your command line. You can pause a task, move it to the background, or bring it back to the foreground.

When you run a command, it usually runs in the foreground. This means it takes control of your terminal, and you can't type new commands until it finishes.

A background process, however, runs independently. It frees up your terminal so you can continue working on other things while it executes.

To pause a currently running foreground process, use the keyboard shortcut Ctrl+Z. This sends a SIGTSTP signal, suspending the process.

The process doesn't terminate; it becomes a 'stopped' job, waiting for you to tell it what to do next.

Once you've paused a process (or sent one to the background), you can see a list of all active jobs in your current shell session using the jobs command.

Each job gets a unique job number (like [1], [2], etc.) and its status (e.g., Stopped, Running).

If you have a stopped or backgrounded job, you can bring it back to the foreground using the fg command, followed by its job number (e.g., %1).

This makes the job the active process in your terminal again.

To resume a stopped job and send it to the background, use the bg command with its job number.

The process will continue running without blocking your terminal, and you'll get your prompt back immediately.

You don't always need to start a process in the foreground and then pause it. You can launch a command directly into the background by appending an ampersand (&) to the end of the command.

This is great for long-running tasks you don't need to interact with.

When you use jobs, you see job numbers like [1], [2]. These are specific to your shell session.

Every running process also has a unique Process ID (PID), which is a system-wide number. You can see PIDs with jobs -l or ps.

To terminate a background or stopped job, you can use the kill command. You can specify the job number (e.g., kill %1) or its PID (e.g., kill 12345).

kill sends a signal to the process. By default, it's SIGTERM (graceful termination). For forceful termination, use kill -9 %job_number or kill -9 PID.

You've started a long-running command (e.g., find / -name *.txt), but now you need your terminal back to type a different command. What's the correct sequence to pause the find command, send it to the background so it continues running, and then confirm it's a background job?

You've mastered job control!

• Ctrl+Z pauses a foreground process.
• jobs lists all active jobs.
• fg %N brings a job N to the foreground.
• bg %N sends a stopped job N to the background.
• Appending & runs a command directly in the background.
• kill %N or kill PID terminates a job.

This allows you to manage multiple tasks efficiently within a single terminal session!