/etc/passwd and /etc/shadow in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this command?

You run the command cut -d: -f1 /etc/passwd | head -3. What is the expected output?

Linux CLI

cut -d: -f1 /etc/passwd | head -3

A

root
sys
adm

B

root
bin
daemon

C

root
daemon
bin

D

daemon
bin
sys

💡 Hint

The first field in /etc/passwd is the username. The command extracts usernames and shows the first three.

The /etc/passwd file lists user accounts. The first three usernames are usually root, daemon, and bin in that order.

🧠 Conceptual

intermediate

What is the main difference between /etc/passwd and /etc/shadow?

Choose the correct statement about the difference between /etc/passwd and /etc/shadow files.

A /etc/passwd is readable by all users, /etc/shadow is readable only by root and stores encrypted passwords.

B /etc/passwd stores encrypted passwords, /etc/shadow stores user IDs.

C /etc/shadow stores usernames, /etc/passwd stores passwords in plain text.

D /etc/passwd and /etc/shadow both store passwords in plain text.

💡 Hint

Think about file permissions and security of password storage.

/etc/passwd contains user account info and is world-readable. /etc/shadow contains encrypted passwords and is only readable by root for security.

🔧 Debug

advanced

Why does this script fail to read /etc/shadow?

A user runs this script to read the first line of /etc/shadow:

#!/bin/bash
head -1 /etc/shadow

But it shows a permission denied error. Why?

A /etc/shadow is only readable by root, normal users cannot read it.

B head command does not work on /etc/shadow file.

C The script is missing execute permission.

D The script syntax is incorrect.

💡 Hint

Check file permissions of /etc/shadow.

/etc/shadow contains sensitive password hashes and is only readable by root. Normal users get permission denied errors.

🚀 Application

advanced

Extract usernames with locked passwords from /etc/shadow

Which command correctly lists usernames whose password field in /etc/shadow starts with an exclamation mark (!) indicating locked accounts?

A sed -n '/^!/p' /etc/shadow

B awk -F: '$2 ~ /^!/ {print $1}' /etc/shadow

C cut -d: -f1 /etc/shadow | grep '!'

D grep '^!' /etc/shadow | cut -d: -f1

💡 Hint

Look for lines where the second field starts with ! and print the first field.

The password field is the second field in /etc/shadow. Using awk with field separator ':' and regex /^!/ on $2 correctly filters locked accounts.

📝 Syntax

expert

What error does this command produce?

What error will this command produce?

cut -d: -f1 /etc/shadow | head -3

A No output, command runs silently

B File not found error

C Syntax error due to wrong delimiter

D Permission denied error because /etc/shadow is restricted

💡 Hint

Consider file permissions of /etc/shadow for normal users.

Normal users cannot read /etc/shadow, so cut command fails with permission denied error.