su (switch user) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the su command do in Linux?

The su command lets you switch from your current user to another user account in the terminal. It stands for "switch user."

beginner

How do you switch to the root user using su?

You type su and press Enter. Then you enter the root user's password when asked. This gives you root access.

intermediate

What is the difference between su and su -?

su switches user but keeps your current environment. su - switches user and loads the new user's full environment, like a fresh login.

beginner

How do you switch to another user named alice using su?

You type su alice and press Enter. Then enter Alice's password when prompted.

beginner

Why might you use exit after using su?

Typing exit logs you out of the switched user session and returns you to your original user.

What does the command su - do differently than su?

A Logs out the current user

B Switches user but keeps the current environment

C Shows the current user name

D Switches user and loads the new user's environment

su - switches user and loads the new user's full environment, like a fresh login.

Which password do you need to enter when you run su alice?

A Alice's password

B Your own password

C Root password

D No password is needed

You must enter the password of the user you want to switch to, in this case, Alice's password.

What happens if you type su without a username?

A Switches to root user

B Switches to guest user

C Shows an error

D Logs out current user

Typing su alone switches to the root user by default.

How do you return to your original user after using su?

A Type <code>logout</code>

B Close the terminal

C Type <code>exit</code>

D Press Ctrl+C

Typing exit ends the switched user session and returns you to your original user.

Why is su useful in Linux?

A To update software automatically

B To switch between different user accounts

C To create new files

D To check disk space

su lets you switch between user accounts in the terminal.

Explain how to switch to the root user using su and how to return to your original user.

Think about logging in as root and then logging out.

Describe the difference between su and su - and when you might use each.

Consider how environment variables and settings change.

Practice

1. What does the su command do in Linux?

easy

A. Updates the system packages

B. Shows the current user's groups

C. Switches the current user to another user

D. Displays the current directory contents

Solution

1. Step 1: Understand the purpose of su

   The su command is used to switch from the current user to another user in the terminal.

2. Step 2: Compare options

   Updating system packages uses apt or yum, showing user's groups uses 'groups', displaying directory contents uses 'ls'. These are unrelated to user switching.

3. Final Answer:

   Switches the current user to another user -> Option C

4. Quick Check:

   su = switch user [OK]

Hint: Remember: su means switch user [OK]

Common Mistakes:

• Confusing su with commands like ls or groups
• Thinking su updates software
• Assuming su shows files

2. Which of these is the correct syntax to switch to user alice and load her full environment?

easy

A. su - alice

B. su alice

C. su --user alice

D. su /alice

Solution

1. Step 1: Recall the syntax for full environment loading

   Using su - username switches user and loads their full environment.

2. Step 2: Check options

   su alice changes user without full environment, su --user alice uses invalid flag, su /alice is invalid syntax.

3. Final Answer:

   su - alice -> Option A

4. Quick Check:

   Use dash (-) to load full environment [OK]

Hint: Use dash (-) after su for full environment [OK]

Common Mistakes:

• Omitting the dash (-) to load environment
• Using wrong flags like --user
• Adding slashes before username

3. What will be the output of the following commands if you run su - bob and enter the correct password?

whoami

medium

A. root

B. Permission denied

C. current user name

D. bob

Solution

1. Step 1: Understand what su - bob does

   This command switches the current user to 'bob' and loads his environment after password verification.

2. Step 2: Check the output of whoami

   After switching, whoami shows the current active user, which will be 'bob'.

3. Final Answer:

   bob -> Option D

4. Quick Check:

   After su, whoami = new user [OK]

Hint: whoami shows switched user after su [OK]

Common Mistakes:

• Expecting root instead of target user
• Thinking it shows original user
• Assuming permission denied without password

4. You try to switch to user john using su john but get the error: Authentication failure. What is the most likely cause?

medium

A. You entered the wrong password for john

B. User john does not exist

C. You forgot to use sudo before su

D. You need to be root to use su

Solution

1. Step 1: Understand the error message

   Authentication failure means the password entered was incorrect for the target user.

2. Step 2: Analyze other options

   User existence error would say 'unknown user'. Using sudo is not required for su. You do not need to be root to switch users if you know the password.

3. Final Answer:

   You entered the wrong password for john -> Option A

4. Quick Check:

   Authentication failure = wrong password [OK]

Hint: Authentication failure means wrong password [OK]

Common Mistakes:

• Assuming user does not exist
• Thinking sudo is required for su
• Believing only root can switch users

5. You want to run a script as user deploy without fully switching to their environment. Which command is best to use?

hard

A. su -c deploy ./script.sh

B. su deploy -c './script.sh'

C. su deploy ./script.sh

D. su - deploy ./script.sh

Solution

1. Step 1: Understand running commands as another user

   Using su username -c 'command' runs the command as that user without opening a full shell.

2. Step 2: Check options for correct syntax

   su -c deploy ./script.sh wrong flag order, su - deploy ./script.sh starts login shell, su deploy ./script.sh starts non-login shell. Only su deploy -c './script.sh' runs directly.

3. Final Answer:

   su deploy -c './script.sh' -> Option B

4. Quick Check:

   Use -c to run command as user [OK]

Hint: Use su -c 'command' to run without full switch [OK]

Common Mistakes:

• Placing - before username incorrectly
• Omitting -c flag for command
• Confusing argument order