UNIX / Linux : How to lock or disable an user account

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There are several ways in which user account can be locked or disabled. The posts discusses few of the most widely used ways.

1. Lock the password

To lock a users account use the command usermod -L or passwd -l. Both the commands adds an exclamation mark (“!”) in the second field of the file /etc/passwd. For example :

# usermod -L testuser

or

 

# passwd -l testuser

2. Expire the user account

The commands passwd -l and usermod -L are ineffcient when it comes to disable/lock user accounts. These commands will not disallow authentication by SSH public keys (or other PAM modules other than pam_unix that may be enabled). Additionally, changing the shell to /bin/false or /sbin/nologin is unsatisfactory to us since this only affects interactive logins. So to completely disable user accounts you can user the command chage -E0. For example :

# chage -E0 testuser

Expiring an account via use of the 8th field in /etc/shadow (using “chage -E”) will block all access methods that use PAM to authenticate a user.

3. Changing the shell

We can also change the default shell of the user to /sbin/nologin so that the user do not get any login shell when he tries to login into the system.

# usermod -s /sbin/nologin [username]

You can check for the 7th and last field in /etc/passwd for the change of shell to /sbin/nologin.

Verify if the account is locked or disabled.

For each of the methods described above, you can verify if the user account is locked/disabled using below methods.

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1. Check if the user account is locked.
Check for the flag *LK* in the below command output which indicates that the account is locked.

# passwd --status root
root *LK* 2017-07-19 0 45 7 -1 (Password set, SHA512 crypt.)

2. Check if the account has an expire date.
Check for the lines Password expires and Account expires to check if the account password is expired.

# chage -l root
Last password change                                    : Jul 19, 2017
Password expires                                        : Sep 02, 2017
Password inactive                                       : never
Account expires                                         : Sep 02, 2017
Minimum number of days between password change          : 0
Maximum number of days between password change          : 45
Number of days of warning before password expires       : 7

3. Check for non-interactive shell
Check if the user shell has been changed to a non-interactive shell like /sbin/nologin.

# grep ^root /etc/passwd
root:x:0:0:root:/root:/sbin/nologin

 

 

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