Background processes (&) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this command sequence?

Consider the following commands run in a Linux shell:

sleep 2 & echo Done

What will be printed immediately after running these commands?

Linux CLI

sleep 2 & echo Done

A Done after 2 seconds

B Done

C No output until sleep finishes

D sleep: command not found

💡 Hint

The ampersand (&) runs the first command in the background, so the shell does not wait for it.

The 'sleep 2 &' runs the sleep command in the background, so the shell immediately runs 'echo Done' and prints 'Done' right away.

💻 Command Output

intermediate

What happens when you run multiple background jobs?

You run these commands in a Linux shell:

sleep 3 & sleep 1 & sleep 2 & wait

What will happen after running these commands?

Linux CLI

sleep 3 & sleep 1 & sleep 2 & wait

A The shell waits until all three sleep commands finish before returning to prompt

B The shell returns immediately without waiting

C Only the first sleep command runs in background, others run in foreground

D The shell waits only for the first sleep command

💡 Hint

The 'wait' command waits for all background jobs to finish.

All three sleep commands run in background because of '&'. The 'wait' command pauses the shell until all background jobs complete.

🔧 Debug

advanced

Why does this background command fail to run properly?

You try to run this command in a shell:

echo Hello & & echo World

What error will the shell produce?

Linux CLI

echo Hello & & echo World

A bash: syntax error near unexpected token `&'

B Hello\nWorld

C No output, command hangs

D Hello

💡 Hint

Check how many ampersands are used and their placement.

The shell sees two ampersands in a row without a command between them, causing a syntax error.

🚀 Application

advanced

How to run a script in background and save its output to a file?

You want to run a script named backup.sh in the background and save both its output and errors to backup.log. Which command does this correctly?

A ./backup.sh >& backup.log &

B ./backup.sh & > backup.log 2>&1

C ./backup.sh &> backup.log 2>&1

D ./backup.sh > backup.log 2>&1 &

💡 Hint

Redirect output before putting command in background.

The correct syntax redirects stdout and stderr to the file, then runs the command in background with '&'.

🧠 Conceptual

expert

What is the effect of running a command with nohup and & together?

You run this command:

nohup longtask.sh &

What happens to the process if you close the terminal?

A The process stops immediately when terminal closes

B The process pauses until terminal is reopened

C The process keeps running even after terminal closes

D The process restarts automatically after terminal closes

💡 Hint

nohup prevents hangup signals from stopping the process.

nohup makes the process ignore hangup signals, so combined with '&' it runs in background and keeps running after terminal closes.