su (switch user) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this command?

You run the command su -c 'whoami' as a normal user. What will be the output if you enter the root password correctly?

Linux CLI

su -c 'whoami'

A root

B normal user name

C su: Authentication failure

D command not found

💡 Hint

The -c option runs a command as the switched user.

The command su -c 'whoami' runs whoami as the root user after successful authentication, so the output is root.

💻 Command Output

intermediate

What happens if you run su without a username?

You type su and press Enter. What user will you switch to after entering the password?

Linux CLI

su

A Switches to root user

B Switches to current user again

C Switches to nobody user

D Shows an error message

💡 Hint

By default, su switches to the superuser if no username is given.

When no username is specified, su switches to the root user after password authentication.

📝 Syntax

advanced

Which command correctly switches to user 'alice' and starts a login shell?

Choose the correct su command to switch to user 'alice' with a login shell.

A su alice --login

B su alice -l

C su - alice

D su -l alice

💡 Hint

The dash - before the username starts a login shell.

The correct syntax is su - alice to start a login shell as user 'alice'.

🔧 Debug

advanced

Why does this command fail with 'Authentication failure'?

You run su - bob but get 'Authentication failure' even though you typed the correct password. What could be the reason?

Linux CLI

su - bob

A You typed the root password instead of bob's password

B User 'bob' does not have a password set

C The 'su' command is not installed

D You are not allowed to run 'su' as a normal user

💡 Hint

Check if the target user has a valid password.

If user 'bob' has no password set, authentication will fail even with the correct password typed.

🚀 Application

expert

How to run a command as another user without switching shell interactively?

You want to run ls /root as root from your normal user account without entering an interactive shell. Which command achieves this?

A su -c ls /root

B su - root -c 'ls /root'

C su -c 'ls /root'

D su root -c 'ls /root'

💡 Hint

Use the dash to start a login shell and the -c option to run a command.

The command su root -c 'ls /root' runs ls /root as root without starting a login shell, without interactive switching.