User accounts are disabled or locked automatically after a specified number of failed login attempts. By default, the maximum failed login attempts is three times.

Once the user account is locked, you will get the following output even if you have the correct username and password.

Please login as root to reset the number of unsuccessful log-in attempts for the admin account, which enables the account if it has been locked out.  

# pam_tally2 -r -u <username>

Sample command output for resetting the user account for admin:

[[email protected] ~]# pam_tally2 -r -u admin
Login           Failures Latest failure     From
admin               0

Synopsis        Description
-u                     username
-r                     reset

The default of three maximum login attempts can be changed by going to the Settings > Security in the GUI.