The “bg” command is a built-in command in Unix-like operating systems that allows users to resume suspended jobs and keep them running in the background. When a job is suspended using the “Ctrl + Z” key combination, it is temporarily halted and placed in the background, allowing the user to perform other tasks in the shell.
The primary purpose of the “bg” command is to bring the suspended job back to the foreground and continue its execution in the background without interrupting the current shell session. This is particularly useful when there are multiple jobs running concurrently, and the user wants to switch between them or free up the terminal for other tasks.
Key features and concepts of the “bg” command include:
- Job Control: The “bg” command is part of the job control functionality provided by Unix-like operating systems. It allows users to manage and control the execution of multiple jobs within a shell session.
- Resuming Suspended Jobs: When a job is suspended using “Ctrl + Z”, it is placed in a suspended state and temporarily stops executing. The “bg” command is used to resume these suspended jobs and move them to the background, where they continue running.
- Background Execution: When a job is running in the background, it does not occupy the foreground of the terminal. This means that the user can continue working in the shell and execute other commands while the background job runs concurrently.
- Job Status: The “bg” command provides information about the status of the job being resumed, such as its process ID (PID) and the job number assigned by the shell. This information can be useful for further management and monitoring of the job.
- Output Handling: By default, the output generated by a background job is not displayed directly on the terminal. Instead, it is typically redirected to a file or discarded. However, the user can redirect the output to a file or use other techniques to capture and view the output if needed.
It is important to note that the “bg” command is used specifically for resuming suspended jobs and moving them to the background. It does not start new processes or manage the execution of commands that were originally intended to run in the background. For starting new background processes, the “&” symbol is commonly used at the end of a command.
bg Command Examples
1. Resume the most recently suspended job and run it in the background:
# bg
2. Resume a specific job (use jobs -l to get its ID) and run it in the background:
# bg %job_id
Summary
In summary, the “bg” command is used to resume suspended jobs and continue their execution in the background. It allows users to manage and control the execution of multiple jobs within a shell session, providing flexibility and concurrency. By using “bg,” users can efficiently switch between jobs and free up the terminal for other tasks while background jobs continue running.