passwd (change password) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the primary purpose of the passwd command in Linux?

The passwd command is used to change a user's password securely on a Linux system.

beginner

Which user can change another user's password using passwd?

Only the root user (administrator) can change other users' passwords using passwd username.

beginner

What happens if you run passwd without any arguments?

It prompts you to change the password of the current logged-in user.

beginner

Why does passwd not show characters when you type your new password?

For security, passwd hides input so no one can see your password as you type.

intermediate

How can you force a user to change their password at next login?

Use passwd -e username to expire the password and require a change on next login.

What does the command passwd do when run by a normal user?

A Deletes the current user's password

B Displays the current user's password

C Changes another user's password

D Changes the current user's password

Running passwd without arguments lets a user change their own password.

Who can change another user's password using passwd username?

A Only root user

B No one can change others' passwords

C Only users in the sudo group

D Any logged-in user

Only the root user has permission to change other users' passwords.

What option forces a user to change their password at next login?

A -e

B -d

C -l

D -r

The -e option expires the password, requiring a change on next login.

Why does passwd not show your password characters when typing?

A Because the terminal is broken

B For security to hide your password

C To save screen space

D Because passwords are not needed

Hiding password input prevents others from seeing your password.

What happens if you run passwd username as root?

A Locks the user account

B Deletes the user

C Changes the password for the specified user

D Displays user info

Root can change any user's password by specifying the username.

Explain how to change your own password using the passwd command.

Think about what happens when you just type 'passwd' and press enter.

Describe how an administrator can force a user to update their password at next login.

Look for the option that expires passwords.

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