#compsci 

## /etc/passwd
The first line in /etc/passwd is:
root:x:0:0:root:/root:/bin/bash

Each line in /etc/passwd is structured in the following way:
1) username
2) password ("x" - means the password is stored in /etc/shadow, "%asterisk%" means the user doesn't have login access and doesn't have a password)
3) the UID
4) the GUID
5) GECOS field - generally used to leave comments about the user or account (comma delimeted: "PulseAudio daemon,,,")
6) home directory
7) user's shell

## /etc/shadow
The file is used to store information about user authentication
The fields are separated by colons as followed:

1) username
2) encrypted password
3) date of the password's last change
4) minimum password age
5) maximum password age
6) password warning period
7) password inactivity period
8) account expiration date
9) reserved field for future use

## /etc/group
Sample line:
root:*:0:pete

The /etc/group fields are as follows:
1) Group name
2) Group password (there is no need to set a group password, so a "*" will be put in place as the default value)
3) GID
4) List of users

## /etc/gshadow

## useradd, userdel, and passwd
useradd - add a user
userdel - delete a user
usermod - modify a user
passwd - change the password of a user