jobs command in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of jobs command with background processes

You run these commands in a Linux shell:

sleep 30 &
sleep 40 &
jobs

What is the expected output of the jobs command?

A

[1]-  Running                 sleep 30 &
[2]+  Running                 sleep 40 &

B No output, jobs command shows nothing

C

[1]+  Done                    sleep 30 &
[2]-  Done                    sleep 40 &

D

[1]+  Running                 sleep 30 &
[2]-  Running                 sleep 40 &

💡 Hint

Jobs are numbered in order started; the last job is marked with a plus (+).

The jobs command lists background jobs with their job numbers. The most recent job is marked with a plus (+) and the previous with a minus (-). Both sleep commands run in background, so status is Running.

💻 Command Output

intermediate

Effect of fg command on jobs

You start a background job:

sleep 60 &

Then run jobs and see:

[1]+  Running                 sleep 60 &

What happens when you run fg %1?

A Syntax error: fg requires a job name, not a number

B The sleep 60 job is terminated immediately

C Nothing happens, job stays in background

D The sleep 60 job moves to foreground and blocks the shell until it finishes

💡 Hint

The fg command brings a background job to foreground.

The fg command resumes the specified job in the foreground, so the shell waits until the job completes.

🔧 Debug

advanced

Why does jobs show no output?

You run this sequence:

sleep 20 &
jobs

But jobs shows no output. What is the most likely reason?

A The jobs command requires root privileges

B The sleep command finished before jobs was run

C The shell session is not interactive, so jobs command shows nothing

D The sleep command was run in foreground, so no jobs exist

💡 Hint

Jobs only work in interactive shells.

The jobs command only reports jobs in interactive shells. In scripts or non-interactive shells, it shows nothing.

🧠 Conceptual

advanced

Understanding job control signals

You have a job running in foreground. You press Ctrl+Z. What happens to the job and how does jobs reflect this?

A The job continues running in background, jobs shows 'Running'

B The job is suspended (stopped), and jobs shows it as 'Stopped'

C The job is terminated, and jobs shows no entry

D The job is paused but jobs shows 'Done'

💡 Hint

Ctrl+Z sends SIGTSTP to suspend the job.

Ctrl+Z suspends the foreground job, stopping it temporarily. The jobs command then lists it as 'Stopped'.

🚀 Application

expert

Counting background jobs with jobs command

You run multiple background jobs:

sleep 10 &
sleep 20 &
sleep 30 &

Write a one-liner command using jobs and other shell tools to count how many background jobs are currently running.

A jobs | grep Running | wc -l

B jobs -p | wc -l

C jobs | wc -l

D ps aux | grep sleep | wc -l

💡 Hint

Filter jobs output for Running status, then count lines.

The command 'jobs | grep Running | wc -l' counts only the lines with 'Running', corresponding to currently running background jobs. Other options may count stopped jobs or unrelated processes.