passwd (change password) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of passwd command with expired password

What is the output when running passwd -e username on a Linux system?

Linux CLI

passwd -e username

A Error: User 'username' does not exist.

B Password expiry information changed.

C Usage: passwd [options] [username]

D Password successfully changed.

💡 Hint

The -e option forces password expiration for the user.

The passwd -e username command expires the user's password immediately, so the user must change it at next login. The output confirms this action.

💻 Command Output

intermediate

Result of passwd command with invalid option

What error message appears when running passwd -z on a Linux system?

Linux CLI

passwd -z

A

passwd: invalid option -- 'z'
Try 'passwd --help' for more information.

B passwd: option requires an argument -- 'z'

C Password successfully updated.

D passwd: unknown command 'z'

💡 Hint

Check how passwd handles unknown options.

The passwd command shows an error for invalid options, indicating the invalid option and suggesting help.

🔧 Debug

advanced

Why does passwd fail with 'Authentication token manipulation error'?

You run passwd to change a user's password but get the error: Authentication token manipulation error. What is the most likely cause?

A The system is out of disk space on the root partition.

B The /etc/passwd file is missing from the system.

C The user is not in the sudoers file and lacks permission to change the password.

D The password entered does not meet complexity requirements.

💡 Hint

Consider permissions needed to update password files.

This error usually happens when the user lacks permission to update password files, often because they are not root or do not have sudo rights.

🚀 Application

advanced

Automate password expiration for multiple users

You want to expire passwords for users alice, bob, and carol using a single shell command. Which command correctly does this?

A passwd -e $(alice bob carol)

B passwd -e alice bob carol

C passwd -e alice && passwd -e bob && passwd -e carol

D for user in alice bob carol; do passwd -e $user; done

💡 Hint

Think about how to run a command multiple times in a loop.

Option D uses a loop to run passwd -e for each user individually, which is the correct approach.

🧠 Conceptual

expert

Understanding passwd password aging options

Which passwd option sets the minimum number of days before a user can change their password again?

A -n

B -w

C -x

D -i

💡 Hint

Minimum days means how soon after a change the password can be changed again.

The -n option sets the minimum number of days between password changes.

Practice

1. What does the passwd command do in Linux?

easy

A. It changes the password of a user securely.

B. It lists all users on the system.

C. It creates a new user account.

D. It deletes a user account.

Solution

1. Step 1: Understand the purpose of passwd

   The passwd command is designed to change user passwords securely on Linux systems.

2. Step 2: Compare options with command function

   Options B, C, and D relate to user management but not password changes. Only It changes the password of a user securely. correctly describes passwd.

3. Final Answer:

   It changes the password of a user securely. -> Option A

4. Quick Check:

   passwd changes passwords = A [OK]

Hint: Remember: passwd is for changing passwords only [OK]

Common Mistakes:

• Confusing passwd with user creation commands
• Thinking passwd lists users
• Assuming passwd deletes accounts

2. Which of the following is the correct syntax to change the password for user alice as root?

easy

A. passwd -p alice

B. passwd -u alice

C. passwd --change alice

D. passwd alice

Solution

1. Step 1: Recall root usage of passwd

   Root can change any user's password by running passwd username.

2. Step 2: Analyze options for correct syntax

   Only passwd alice uses the correct syntax. Options A, B, and C use invalid or non-existent flags.

3. Final Answer:

   passwd alice -> Option D

4. Quick Check:

   Root changes user password with passwd username = D [OK]

Hint: Use passwd username as root to change others' passwords [OK]

Common Mistakes:

• Adding wrong flags like -u or -p
• Using --change which is not a valid option
• Trying to change password without specifying username as root

3. What will happen if a normal user runs the command passwd root?

medium

A. The root password will be changed immediately.

B. The user will be prompted to enter the current root password.

C. The command will fail with a permission error.

D. The user's own password will be changed instead.

Solution

1. Step 1: Understand user permissions for passwd

   Only root can change other users' passwords. Normal users cannot change root's password.

2. Step 2: Predict command behavior for normal user

   When a normal user tries passwd root, the system denies permission and shows an error.

3. Final Answer:

   The command will fail with a permission error. -> Option C

4. Quick Check:

   Normal user cannot change root password = A [OK]

Hint: Only root can change other users' passwords; others get permission error [OK]

Common Mistakes:

• Assuming normal user can change root password
• Thinking user will be asked root's current password
• Believing user's own password changes instead

4. You run passwd alice as root but get the error: passwd: Authentication token manipulation error. What is the most likely cause?

medium

A. The password entered does not meet complexity rules.

B. You forgot to run the command with sudo or as root.

C. The user alice does not exist.

D. The passwd command is not installed.

Solution

1. Step 1: Understand the error meaning

   The error usually means insufficient permissions to update password files.

2. Step 2: Identify cause based on command context

   If not run as root or with sudo, passwd cannot change another user's password, causing this error.

3. Final Answer:

   You forgot to run the command with sudo or as root. -> Option B

4. Quick Check:

   Permission error means missing root privileges = C [OK]

Hint: Run passwd with root or sudo to avoid permission errors [OK]

Common Mistakes:

• Assuming user does not exist without checking
• Thinking password complexity causes this error
• Believing passwd is missing from system

5. You want to automate changing passwords for multiple users listed in a file users.txt. Which script snippet correctly changes each user's password to NewPass123 using passwd?

hard

A. for user in $(cat users.txt); do echo -e "NewPass123\nNewPass123" | passwd $user; done

B. while read user; do echo "NewPass123" | passwd --stdin $user; done < users.txt

C. for user in users.txt; do passwd $user NewPass123; done

D. cat users.txt | passwd -p NewPass123

Solution

1. Step 1: Understand how to feed password to passwd

   The passwd command reads password from standard input when piped, requiring password twice (new and confirmation).

2. Step 2: Analyze each script snippet

   while read user; do echo "NewPass123" | passwd --stdin $user; done < users.txt uses --stdin which is not standard on all systems. for user in $(cat users.txt); do echo -e "NewPass123\nNewPass123" | passwd $user; done correctly uses echo -e to send password twice piped to passwd. for user in users.txt; do passwd $user NewPass123; done incorrectly treats file name as user list. cat users.txt | passwd -p NewPass123 misuses passwd with pipe and -p which is invalid.

3. Final Answer:

   for user in $(cat users.txt); do echo -e "NewPass123\nNewPass123" | passwd $user; done -> Option A

4. Quick Check:

   Pipe password twice to passwd in loop = B [OK]

Hint: Pipe password twice with echo -e inside loop to automate [OK]

Common Mistakes:

• Using non-standard --stdin option
• Not sending password twice for confirmation
• Treating filename as username list without reading
• Misusing passwd options