User administration Linux

1. 1) /etc/passwd

The file where system user account definition is done is /etc/passwd. This file has the following structure :

$ cat /etc/passwd
...
username:x:500:600:Some comments:/home/username:/bin/bash
...

username
The system account username . It should not start with a number or include uppercase letters.

x
The password. An x points to /etc/shadow for the password. An * means the account is disabled.