/etc/passwd and /etc/shadow in Linux CLI - Step-by-Step Execution

Concept Flow - /etc/passwd and /etc/shadow

Read /etc/passwd

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Parse user info: username, UID, GID, home, shell

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Check password field in /etc/passwd

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Read /etc/shadow for encrypted password

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Verify password or manage user authentication

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Use info for login or system tasks

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End

The system reads /etc/passwd for user info, then checks /etc/shadow for secure password data to authenticate users.

Execution Sample

Linux CLI

cat /etc/passwd
cat /etc/shadow

Shows the contents of /etc/passwd and /etc/shadow files to see user info and encrypted passwords.

Execution Table

Step	Command	Action	Output Example	Notes
1	cat /etc/passwd	Read user account info	root:x:0:0:root:/root:/bin/bash user1:x:1000:1000::/home/user1:/bin/bash	Password field is 'x' meaning password is in /etc/shadow
2	cat /etc/shadow	Read encrypted passwords	root:$6$abc123$encryptedhash...:18295:0:99999:7::: user1:$6$def456$encryptedhash...:18295:0:99999:7:::	Passwords are hashed and secured
3	Check password field in /etc/passwd	Find 'x' or '*'	'x' found	Indicates password stored in /etc/shadow
4	Use info for login	Authenticate user by comparing password hash	Success or failure	System uses /etc/shadow hash to verify password
5	End	No more steps	N/A	Process complete

💡 Finished reading user info and password hashes for authentication

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
passwd_content		root:x:0:0:root:/root:/bin/bash user1:x:1000:1000::/home/user1:/bin/bash	Same	Same	Same
shadow_content			root:$6$abc123$encryptedhash... user1:$6$def456$encryptedhash...	Same	Same
password_field				'x'	'x' means password in shadow file

Key Moments - 3 Insights

Why does /etc/passwd show 'x' in the password field instead of the actual password?

Because the actual encrypted passwords are stored securely in /etc/shadow, not in /etc/passwd. See execution_table step 3 where 'x' indicates this.

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

/etc/passwd contains user info like username and home directory, while /etc/shadow stores encrypted passwords securely. This separation improves security (see execution_table steps 1 and 2).

Can a normal user read /etc/shadow?

No, /etc/shadow has restricted permissions to protect password hashes. Only root or privileged processes can read it (implied in execution_table step 2).

Visual Quiz - 3 Questions

Look at the execution table, what does the 'x' in the password field of /etc/passwd mean at step 3?

A Password is stored in /etc/shadow

B Password is empty

C Password is stored in /etc/passwd

D User account is disabled

💡 Hint

Refer to execution_table row 3 under 'Notes' explaining the meaning of 'x'

At which step do we see the encrypted password hashes?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Check execution_table row 2 under 'Output Example' for encrypted hashes

If /etc/shadow is unreadable, what impact does it have on user authentication?

A Users can still log in with passwords

B System cannot verify passwords, login fails

C Passwords are read from /etc/passwd instead

D User accounts are deleted

💡 Hint

Refer to execution_table step 4 where password verification uses /etc/shadow

Concept Snapshot

/etc/passwd stores user info like username, UID, home directory.
Password field shows 'x' or '*' if password is in /etc/shadow.
/etc/shadow stores encrypted passwords securely with restricted access.
System reads /etc/passwd first, then /etc/shadow to authenticate users.
This separation protects password security on Linux systems.

Full Transcript

The /etc/passwd file contains basic user account information such as username, user ID, group ID, home directory, and default shell. However, it does not store actual passwords for security reasons. Instead, the password field in /etc/passwd usually contains an 'x' or '*', indicating that the encrypted password is stored in the /etc/shadow file. The /etc/shadow file holds the hashed passwords and has restricted permissions to protect this sensitive data. When a user logs in, the system reads /etc/passwd to find the user details, then reads /etc/shadow to verify the password by comparing the entered password's hash with the stored hash. This two-file system improves security by limiting access to password hashes. Normal users cannot read /etc/shadow, only privileged users or processes can. This separation is essential for safe user authentication on Linux systems.