A user is a person who enters into the computer system for specific task is called user,when we create a user in linux,system create a user configuration and directory.this configuration file and directory store information about users.this configuration file includes home directory,login shell,password.group,encrypted pasword,encrypted password for group,default login.
There are two type of users - 1.Super User 2.Local User, super user is also called system administration,he/she is head of the computer department.he/she is the root user.he/she has all root access,all other users than super user are called local user,they have limited computer access.basically local users are logged into computer system for thir work.
The 'root' account is the most privileged account on a unix system.this account gives you the ability to carry out all side of system administration,including adding accounts,changing user password,examinig log file,installing software,etc.
The 'root' account has no security restrictions imposed upon it.this means it is easy to perform administrative duties without disturbance.however,the system assumes you know what you are doing and will do exactly what you request.
In this example,linux use shadow password suite,the shadow suite is fairly easy to install and will automatically convert your non-shadow password file format over to the new shadow format.there are two steps to creating a new user account.
The first step to actually create the account itself,the second is to provide an alias to thir e-mail address for example "firstname.lastname@example.org".
The username is at most 8 characters login,and whenever possible you should choose thir last name,or last name and first initial if a user account already exists(the add user script will detect and prevent you from adding,duplicate account names).
You will then be prompted to enter other information,full name of user,user group(usually the default value), a user id# (automatically assigned),home directory,(automatically assigned),a user shell,some password expiration values,and finally the desired password(which won't echo to the screen,you should have the user choose a password between 6 to 8 characters in length for security reasons).