What does the '-u' option do in the 'passwd' command?

The -u option in the passwd command is used to unlock a user account that has been locked. When a user account is locked, the user cannot log in. By using passwd -u username, you can unlock the specified user account, allowing the user to log in again.

Here's an example of how to use it:

sudo passwd -u username

Replace username with the actual username of the account you want to unlock.