fg and bg commands in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this sequence of commands?

You run the following commands in a Linux shell:

sleep 30 &
jobs
fg %1

What will the jobs command output before fg %1 is run?

Linux CLI

sleep 30 &
jobs
fg %1

A [1]+ Done sleep 30

B [1]+ Stopped sleep 30

C [1]- Running sleep 30 &

D [1]+ Running sleep 30 &

💡 Hint

Think about what happens when a command is run in the background with & and how jobs lists them.

When you run 'sleep 30 &' the job runs in the background and is marked as 'Running'. The jobs command shows it with a plus sign for the current job and the '&' indicates background.

💻 Command Output

intermediate

What happens after running bg on a stopped job?

You start a command and stop it with Ctrl+Z. Then you run bg %1. What will be the job status if you run jobs immediately after?

Linux CLI

sleep 30
# Press Ctrl+Z to stop
bg %1
jobs

A [1]+ Stopped sleep 30

B [1]+ Running sleep 30 &

C [1]+ Done sleep 30

D [1]+ Terminated sleep 30

💡 Hint

bg resumes a stopped job in the background.

The bg command resumes the stopped job in the background, so jobs will show it as Running with an ampersand.

📝 Syntax

advanced

Which command correctly brings job 2 to the foreground?

You have multiple jobs running. Which of these commands correctly brings job number 2 to the foreground?

A fg %2

B fg job2

C fg 2

D fg #2

💡 Hint

Jobs are referenced by a percent sign followed by the job number.

The correct syntax to bring job number 2 to foreground is 'fg %2'. 'fg 2' is invalid because it lacks the percent sign. 'fg job2' and 'fg #2' are invalid syntaxes.

🔧 Debug

advanced

Why does this bg command fail with 'no such job' error?

You run:
sleep 100 &
bg %1

But get the error: 'bg: no such job'. Why?

Linux CLI

sleep 100 &
bg %1

A Because the percent sign is missing in the command.

B Because the job number 1 does not exist yet.

C Because bg requires the job to be stopped, not running.

D Because the job is already running in the background, bg cannot resume it.

💡 Hint

bg only works on stopped jobs.

The bg command resumes stopped jobs in the background. If the job is already running, bg cannot resume it and gives 'no such job' error.

🚀 Application

expert

How to bring the most recent stopped job to foreground using a single command?

You have multiple jobs stopped and running. Which command brings the most recent stopped job to the foreground?

A fg %+

B fg %%

C fg %-

D fg %1

💡 Hint

The %+ symbol refers to the current job.

In job control, '%+' refers to the current job, which is usually the most recent stopped or background job. Using 'fg %+' brings it to foreground.