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Understanding and Controlling Jobs (jobs, bg, fg)

In Linux, a job refers to a running process, but jobs are managed with a specific set of commands. Unlike processes, which run independently, jobs are associated with a user’s terminal session. The key job-related commands in Linux allow users to monitor, control, and manipulate running jobs. These commands are essential for handling tasks like sending processes to the background or bringing them to the foreground.

In this lesson, we will cover the following commands to manage jobs:

  • jobs – List jobs associated with the current terminal.
  • bg – Resume a job in the background.
  • fg – Bring a job to the foreground.

1. Understanding Jobs with jobs​

The jobs command displays the list of jobs running in the current session. Each job has a job ID and status (running, stopped, etc.). This command is typically used to track the state of background tasks or jobs that have been paused.

Basic Syntax:​

jobs [options]

Common Options:​

OptionDescription
-lList jobs with process IDs (PIDs).
-nShow only jobs that have been started in the last session.
-pDisplay only job PIDs.

Example Usage:​

1. View all jobs:​

jobs

Example output:

[1]+ 1234 Stopped   nano myfile.txt
[2]- 5678 Running   python3 myscript.py &

In this output:

  • Job 1 is stopped (paused) and is running nano on myfile.txt.
  • Job 2 is running in the background, executing python3 myscript.py.

2. List jobs with process IDs:​

jobs -l

3. List only job PIDs:​

jobs -p

2. Running Jobs in the Background with bg​

The bg command is used to resume a paused job and run it in the background. Jobs that are sent to the background continue running, but they no longer occupy the terminal's main screen.

Basic Syntax:​

bg [job_id]

Example Usage:​

1. Send a job to the background:​

When you start a process and press Ctrl+Z (pause), it will stop running. You can then resume the job in the background.

Example:​

  1. Open nano to edit a file, then press Ctrl+Z to pause it.
  2. Now, to resume it in the background, use the bg command with the job ID:
bg %1

2. Send the most recent stopped job to the background:​

If you have multiple jobs stopped, you can resume the most recent one by omitting the job ID:

bg

This will resume the most recently paused job.

3. Bringing Jobs to the Foreground with fg​

The fg command brings a job from the background to the foreground, meaning that it will be the active process in the terminal. You can interact with the process directly again.

Basic Syntax:​

fg [job_id]

Example Usage:​

1. Bring a specific job to the foreground:​

If you want to bring a job, say job 1, to the foreground:

fg %1

2. Bring the most recent background job to the foreground:​

To bring the most recent background job to the foreground, simply use:

fg

This will move the last job run in the background to the foreground.

4. Stopping Jobs​

You can pause or stop a running job in the terminal using Ctrl+Z. This does not terminate the process; it simply pauses it and moves it into a stopped state.

Once a job is stopped, you can either:

  • Resume it in the background using bg.
  • Bring it back to the foreground using fg.

Job Management Workflow​

Here's an example workflow for managing jobs in a terminal session:

  1. Start a command that runs in the foreground (e.g., nano):
nano myfile.txt

  1. Press Ctrl+Z to pause the job and put it into the stopped state.

  2. List all jobs using jobs:

jobs
  1. Send the paused job to the background:
bg %1
  1. Bring the job back to the foreground:
fg %1
  1. To stop the job completely, press Ctrl+C or use the kill command.

Key Takeaways:​

  • jobs displays all active jobs and their status (running, stopped).
  • bg resumes a paused job in the background, allowing the terminal to be used for other tasks.
  • fg brings a background job to the foreground, making it the active process in the terminal.

These commands provide effective control over processes that may not require continuous terminal interaction.

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