Files Description
/etc/passwd Where the user's name, and other pertinent information are stored. This includes the password unless your system is using shadow passwords.
/etc/shadow Where the user's password is stored if you are using shadow passwords.
/etc/group Where group names are stored.
/etc/aliases Where the user's name is matched to a nickname for e-mail.
/etc/sudoers A list of users with special privileges along with the commands they can execute.