Add or Remove Users in FreeBSD Groups
After installing FreeBSD, regular users are not allowed to log in as the "root" user via the "su -" command. The following procedure shows how to grant superuser access for administrative convenience, assuming that the regular user knows the superuser password.
1. Access "root" from login screen.
2. Add a user to the group.
root@host: # pw groupmod wheel -m username
3. Check if such user has been added to the group.
root@host: # pw groupshow wheel
/* The added user needs to log out and log in again for the changes to take effect. */
4. Remove a user from the group.
root@host: # pw groupmod wheel -d username
5. Log out from "root".
root@host: # exit
1. The FreeBSD Documentation Project. FreeBSD Handbook. Section 3.3, "Users and Basic Account Management".