HOW IS THE UNIX PASSWORD FILE SETUP?

The password file is usually called /etc/passwd
Each line of the passwd file of a UNIX system follows the following
format: userid:password:userid#:groupid#:GECOS field:home dir:shell


What each of these fields mean/do---
userid -=> the userid name, entered at login and is what the login searches the file for. Can be a name or a number.

password -=> the password is written here in encrypted form. The encryption is one way only. When a login occurs the password entered is run through the encryption algorithm (along with a salt) and thencontrasted to the version in the passwd file that exists for the login name entered. If they match, then the login is allowed. If not, the password is declared invalid.

userid# -=> a unique number assigned to each user, used for permissions

groupid# -=> similar to userid#, but controls the group the user belongs to. To see the names of various groups check /etc/group

GECOS FIELD -=> this field is where information about the user isstored. Usually in the format full name, office
number, phone number, home phone.Also good source of info to try and crack a password.

home dir -=> is the directory where the user goes into
the system at (and usually should brought
to when a cd is done)

shell -=> this is the name of the shell which is
automatically started for the login

Note that all the fields are separated by colons in the passwd file.

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WHAT DO THOSE *s, !s, AND OTHER SYMBOLS MEAN IN THE PASSWD FILE?
Those mean that the password is shadowed in another file. You have to find out what file, where it is and so on. Ask somebody on your system about the specifics of the Yellow Pages system, but discretely!

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WHAT IS A UNIX TRIPWIRE?
(from Belisarius)
Tripwire is a tool for Uni