whoami and id commands in Linux CLI - Mini Project: Build & Apply

Using whoami and id Commands in Linux

📖 Scenario: You are working on a Linux system and want to learn how to find out your current username and user ID information using simple commands.

🎯 Goal: Learn to use the whoami command to display your current username and the id command to show your user ID, group ID, and group memberships.

📋 What You'll Learn

Use the whoami command to display the current username.

Use the id command to display user ID and group information.

💡 Why This Matters

🌍 Real World

Knowing your username and user ID is important for managing permissions and running commands with the right access on Linux systems.

💼 Career

System administrators and developers often need to check user identity and permissions quickly using these commands.

1

Display your current username using whoami

Type the command whoami to display your current username.

Linux CLI

# Type whoami command below
# Your code here

Hint

The whoami command shows the username you are logged in as.

2

Display your user ID and group information using id

Type the command id to display your user ID, group ID, and groups you belong to.

Linux CLI

whoami
# Type id command below
# Your code here

Hint

The id command shows detailed user and group information.

3

Use id command with your username

Use the command id $(whoami) to display the user ID and group information for your current username explicitly.

Linux CLI

whoami
id
# Type id command with $(whoami) below
# Your code here

Hint

This runs id on the username returned by whoami.

4

Display only your user ID using id

Use the command id -u to display only your numeric user ID.

Linux CLI

whoami
id
id $(whoami)
# Type id -u command below
# Your code here

Hint

The id -u command shows only your user ID number. The exact number depends on your system.

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