bg - Linux

Overview

The bg command in Linux is used to resume suspended jobs in the background. Originally designed for usage in a POSIX shell environment, bg restarts a suspended job without requiring user interaction at the terminal. It is especially useful in multitasking environments where users need to continue working with the terminal while a process runs in the background.

Syntax

The basic syntax of the bg command is:

bg [options] [job_spec...]
  • job_spec: Specifies the job to be put in the background. If no job_spec is provided, the current job is used.

Options/Flags

The bg command usually does not have many options. Here are a couple of common ones:

  • -l: Lists the job after moving it to the background.
  • [job_spec]: Instead of an option, you can specify a job number (e.g., %1 for job 1) to put into the background.

Examples

  1. Basic Example
    Resume the most recently suspended job in the background:

    bg

  2. Specific Job
    Resume a specific job (job number 2 in this case) in the background:

    bg %2

  3. Multiple Jobs
    Resume multiple specific jobs in the background:

    bg %1 %3 %5

Common Issues

  • Job Specification Error: If a non-existent job is referenced, you will receive an error, no such job. Always check existing jobs with the jobs command.
  • Permission Issues: Sometimes, jobs cannot be moved to the background due to permissions, particularly when dealing with system processes or those owned by other users.

Integration

The bg command can be integrated with other commands for powerful scripting and process management. Here’s an example of using bg with grep and jobs:

grep -r "searchText" /some/path/ &
bg
jobs

This command sequence starts a grep search in the background, resumes any stopped job with bg, and lists all current jobs.

  • fg: Brings jobs to the foreground for interactive processing.
  • jobs: Lists the jobs with their statuses, helping to identify job numbers for use with bg and fg.
  • kill: Used to send signals to jobs, which can be used to stop or control various background or foreground processes.

For further reading on bg and job control in bash, the GNU Bash documentation (link) provides comprehensive insights.