How do I unlock an user account (user login id) under Linux operating systems?
The passwd command, used for changing passwords as well used for locking and unlocking accounts on Linux and Unix-like operating systems.
Linux: Unlocking An Account Syntax
The syntax is as follows:
passwd -u username
To unlock the password of the named account called vivek, type:
passwd -u vivek
This option re-enables a password by changing the password back to its previous value (to the value before using the -l option).