[linux] Understanding the 'fg' Command

Introduction

In Linux, the fg command is used to bring a background job to the foreground. When a process is running in the background and you want to interact with it, you can use fg to switch it to the foreground. This can be useful when you have multiple tasks running simultaneously and need to prioritize one over the others.

Syntax

The basic syntax of the fg command is:

fg [job_spec]

Here, job_spec is the job ID of the background process you want to bring to the foreground. If you do not specify a job_spec, the last background process started will be brought to the foreground.

Examples

1. Bringing the last background process to the foreground:

   $ sleep 60 &
   [1] 1234
   $ fg
   

   In this example, the sleep 60 process is started in the background and its job ID is 1. The fg command brings this process to the foreground.

2. Bringing a specific background process to the foreground:

   $ sleep 120 &
   [2] 5678
   $ fg 2
   

   Here, the sleep 120 process is started in the background with job ID 2. By specifying 2 after the fg command, we bring this specific process to the foreground.

3. Using fg with job control:

   $ vi filename.txt
   Ctrl + Z
   $ bg
   $ fg
   

   In this example, we start editing a file with vi and suspend the process with Ctrl + Z. Then, we resume it in the background with bg and finally bring it back to the foreground with fg.

Applicable Versions

The fg command is a part of the GNU Core Utilities package which is available on most Linux distributions. It can be used on systems running bash or other compatible shells.

Overall, the fg command is a handy tool for managing background processes in a Linux environment. Whether you need to prioritize a certain task or interact with a background process, fg allows you to easily bring it to the foreground and continue working on it seamlessly.