Well, as is indicated by their names, UserID is what identifies you to the machine you are logging in to. The Password is a (hopefully) unique string that only the owner of that account should know. This keeps others from logging in to your account.
The Unix password file (/etc/passwd) contains the following fields for each user ->
name:passwd:uid:gid:gecos:dir:shell
* The name is the UserID.
* Password is, well, the password (This is either stored in encrypted form, so that no one can know your password just by looking at this file, or stored in a different file, called 'shadow'. If the password is stored elsewhere, there will be an 'x' in the password field).
* The UID is your UserID - a number unique to your system that identifies you to the computer ( sort of like a hostname like
slashdot.org is another name for the IP address
64.28.67.150 ).
* The GID is a GroupID - you can belong to different groups to identify you further.
* GECOS is leftover from the old (you guessed it) GECOS operating system - this give even friendlier information, depending on how it is set up, like your full name, department, office number, phone number, so on...
* The DIR is your home directory - when you log in, this is where you will be, and most likely where you store all of your files.
* The shell field tells the computer what "shell" to use, like ksh, sh, bash, csh, and so on... The shell is what you type into - it "translates" to make the commands you type run. It talks (pretty much) directly to the core of the Operating System.
Anyhow, this now concludes the short passwd tutorial. Hope that helped!
