Linux bg Command: Details and Examples

The bg command in Linux is used to resume a suspended job in the background, allowing it to continue running without occupying the terminal. This is particularly useful for multitasking in a terminal environment.

Syntax

Where job_spec is the job ID or job number (e.g., %1) of the suspended job. If no job specification is provided, the most recently suspended job is resumed in the background.

Key Details

Examples

Example 1: Resuming a Suspended Job

Start a long-running process, suspend it, and resume it in the background.

$ sleep 100
^Z
[1]+  Stopped                 sleep 100
$ bg
[1]+ sleep 100 &
$ jobs
[1]+  Running                 sleep 100 &

Explanation: The sleep 100 command is started, suspended with Ctrl+Z, and then resumed in the background with bg.

Example 2: Specifying a Job ID

Run multiple jobs, suspend them, and resume a specific job in the background.

$ find / -name "*.txt" 2>/dev/null
^Z
[1]+  Stopped                 find / -name "*.txt"
$ sleep 200
^Z
[2]+  Stopped                 sleep 200
$ bg %1
[1]+ find / -name "*.txt" &
$ jobs
[1]+  Running                 find / -name "*.txt" &
[2]-  Stopped                 sleep 200

Explanation: Two jobs are suspended. bg %1 resumes the first job (find) in the background.

Example 3: Running a Script in the Background

Start a script, suspend it, and resume it in the background.

$ ./long_running_script.sh
^Z
[1]+  Stopped                 ./long_running_script.sh
$ bg
[1]+ ./long_running_script.sh &

Explanation: A script is started, suspended, and then resumed in the background with bg.

Example 4: Combining with `fg`

Move a job to the background and later bring it back to the foreground.

$ tar -zcf archive.tar.gz /home/user
^Z
[1]+  Stopped                 tar -zcf archive.tar.gz /home/user
$ bg
[1]+ tar -zcf archive.tar.gz /home/user &
$ fg %1
tar -zcf archive.tar.gz /home/user

Explanation: The tar command is suspended, moved to the background with bg, and later brought to the foreground with fg %1.

Example 5: Checking Job Status

Verify the status of background jobs after using bg.

$ ping google.com
^Z
[1]+  Stopped                 ping google.com
$ bg
[1]+ ping google.com &
$ jobs
[1]+  Running                 ping google.com &

Explanation: The ping command is suspended and resumed in the background. jobs shows its status.

Example 6: Starting a Job Directly in the Background

Although not using bg directly, you can start a job in the background using &.

$ sleep 300 &
[1] 12345
$ jobs
[1]+  Running                 sleep 300 &

Explanation: The & operator starts the job in the background immediately, bypassing the need for bg.

Example 7: Multiple Background Jobs

Manage multiple suspended jobs and resume them selectively.

$ sleep 100
^Z
[1]+  Stopped                 sleep 100
$ sleep 200
^Z
[2]+  Stopped                 sleep 200
$ bg %2
[2]+ sleep 200 &
$ jobs
[1]+  Stopped                 sleep 100
[2]-  Running                 sleep 200 &

Explanation: Two jobs are suspended, and bg %2 resumes the second job in the background.

Example 8: Using with Long-Running Downloads

Resume a download process in the background.

$ wget http://example.com/largefile.zip
^Z
[1]+  Stopped                 wget http://example.com/largefile.zip
$ bg
[1]+ wget http://example.com/largefile.zip &

Explanation: A download with wget is suspended and resumed in the background.

Example 9: Handling Non-Existent Job

Attempt to resume a non-existent job.

$ bg %3
bash: bg: %3: no such job

Explanation: If the specified job ID does not exist, bg returns an error.

Example 10: Using with a Loop

Suspend a loop and resume it in the background.

$ while true; do echo "Running..."; sleep 1; done
^Z
[1]+  Stopped                 while true; do echo "Running..."; sleep 1; done
$ bg
[1]+ while true; do echo "Running..."; sleep 1; done &

Explanation: A loop is suspended and resumed in the background, continuing to print output.

Note: Use the jobs command to list all jobs and their IDs. To bring a background job to the foreground, use fg [job_spec]. To terminate a job, use kill [job_spec].