whoami and id commands in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of whoami command

What is the output of the whoami command when run by a logged-in user named alice?

Linux CLI

whoami

A id

B alice

C users

D root

💡 Hint

The whoami command shows the current user's login name.

The whoami command prints the username of the current user running the command. If the user is 'alice', it outputs 'alice'.

💻 Command Output

intermediate

Understanding id command output

What does the id command output show when run by user bob with UID 1001, GID 1001, and groups 1001 and 27?

Linux CLI

id

A user=bob uid=1001 gid=1001 groups=1001,27

B bob 1001 1001 27

C uid=1001(bob) gid=1001(bob) groups=1001(bob),27(sudo)

D uid=bob gid=1001 groups=27

💡 Hint

The id command shows user ID, group ID, and group memberships with names.

The id command outputs the user ID (uid), group ID (gid), and all groups the user belongs to, showing both numeric IDs and names.

🧠 Conceptual

advanced

Difference between whoami and id commands

Which statement correctly describes the difference between whoami and id commands?

A <code>whoami</code> shows only the current username; <code>id</code> shows user and group IDs and group memberships.

B <code>whoami</code> shows user and group IDs; <code>id</code> shows only the username.

C <code>whoami</code> shows all logged-in users; <code>id</code> shows current user only.

D <code>whoami</code> shows group memberships; <code>id</code> shows the current username.

💡 Hint

Think about what each command prints about the user.

whoami prints the username of the current user. id prints detailed info: user ID, group ID, and all groups the user belongs to.

💻 Command Output

advanced

Output of id command with multiple groups

What is the output of id for user carol with UID 2000, GID 3000, and groups 3000, 4, and 27, where group 4 is 'adm' and 27 is 'sudo'?

Linux CLI

id

A uid=carol gid=3000 groups=4,27

B uid=2000 gid=3000 groups=carol,adm,sudo

C carol 2000 3000 4 27

D uid=2000(carol) gid=3000(carol) groups=3000(carol),4(adm),27(sudo)

💡 Hint

The id command shows numeric IDs and group names.

The output format includes numeric IDs and names for user ID, group ID, and all groups the user belongs to.

💻 Command Output

expert

Error when running id with invalid option

What error message appears when running id --unknown on a Linux system?

Linux CLI

id --unknown

A

id: unrecognized option '--unknown'
Try 'id --help' for more information.

B id: invalid argument '--unknown'

C bash: id: command not found

D id: option requires an argument -- 'unknown'

💡 Hint

Invalid options usually produce a message about unrecognized option.

The id command prints an error message about unrecognized option and suggests using --help.

Practice

1. What does the whoami command display when run in a Linux terminal?

easy

A. The current logged-in username

B. The current directory path

C. The list of running processes

D. The system's IP address

Solution

1. Step 1: Understand the purpose of whoami

   The whoami command is designed to show the username of the current user logged into the shell.

2. Step 2: Compare with other options

   Options A, B, and C describe other commands or outputs unrelated to whoami.

3. Final Answer:

   The current logged-in username -> Option A

4. Quick Check:

   whoami = username [OK]

Hint: Remember: whoami = "Who am I?" shows your username [OK]

Common Mistakes:

• Confusing whoami with pwd (current directory)
• Thinking whoami shows system info
• Mixing up with commands showing processes

2. Which of the following is the correct syntax to display your user ID and group information in Linux?

easy

A. user id

B. id

C. whoami -u

D. showid

Solution

1. Step 1: Identify the correct command syntax

   The command id without arguments shows user ID, group ID, and group memberships.

2. Step 2: Check other options for validity

   Options A, B, and D are invalid commands or incorrect syntax for this purpose.

3. Final Answer:

   id -> Option B

4. Quick Check:

   id shows user and group info [OK]

Hint: Use simple id to see user and group IDs [OK]

Common Mistakes:

• Adding wrong flags to whoami
• Typing commands with spaces like 'user id'
• Using non-existent commands like showid

3. What will be the output of the command id -u if the current user has user ID 1001?

medium

A. 1001

B. uid=1001(user)

C. user=1001

D. id: invalid option

Solution

1. Step 1: Understand the -u option of id

   The -u option prints only the numeric user ID (UID) of the current user.

2. Step 2: Match output format

   The output will be just the number 1001, not a string with 'uid=' or other text.

3. Final Answer:

   1001 -> Option A

4. Quick Check:

   id -u = UID number only [OK]

Hint: id -u prints only your numeric user ID [OK]

Common Mistakes:

• Expecting full id output with -u
• Confusing uid= prefix with plain number
• Thinking -u is invalid option

4. You run the command id -u but get an error: "id: invalid option -- 'U'". What is the likely cause?

medium

A. You ran the command as root user

B. Your Linux system does not support the id command

C. You used a space between id and -u

D. You typed a capital U instead of lowercase u

Solution

1. Step 1: Check the option case sensitivity

   Linux commands are case sensitive. The option -u is lowercase. Using uppercase -U instead of lowercase -u can cause errors.

2. Step 2: Analyze the error message

   The error "invalid option -- 'U'" suggests the option letter was not recognized, likely due to uppercase letter typed instead of lowercase.

3. Final Answer:

   You typed a capital U instead of lowercase u -> Option D

4. Quick Check:

   Linux options are case sensitive [OK]

Hint: Check option letter case carefully; Linux is case sensitive [OK]

Common Mistakes:

• Typing uppercase instead of lowercase option
• Assuming id command is missing
• Adding spaces incorrectly in command

5. You want to write a script that prints your username and all group names you belong to. Which combination of commands will achieve this?

hard

A. id -un && id -G

B. whoami -g && id -u

C. echo $(whoami) && id -Gn

D. whoami && id -G

Solution

1. Step 1: Identify command to print username

   whoami prints the current username. Using echo $(whoami) prints it clearly.

2. Step 2: Identify command to print group names

   id -Gn prints all group names the user belongs to, separated by spaces.

3. Step 3: Evaluate options

   echo $(whoami) && id -Gn correctly combines username and group names. whoami -g && id -u uses invalid whoami -g. id -un && id -G uses id -un (which prints username) and id -G (which prints numeric group IDs, not names). whoami && id -G prints username and numeric group IDs, not names.

4. Final Answer:

   echo $(whoami) && id -Gn -> Option C

5. Quick Check:

   Use whoami + id -Gn for username and group names [OK]

Hint: Use whoami for username and id -Gn for group names [OK]

Common Mistakes:

• Using invalid flags with whoami
• Confusing numeric IDs with names
• Not combining commands properly