1. Adding New Users

2. User Accounts
Typically, a user is an individual who can log in, edit files, run programs and make use of the system. Each user has a username (login name), a UID, one or more groups, and GIDs.
User account information is stored primarily in the password file, found in /etc/passwd. The group information is stored in the group file found in /etc/group. These are both public files, where all users can read them but only root can modify them.

3. Adding New User Adding a new user can be divided into several steps:
Assign a user a name, a UID, primary group and decide which other groups she should be a member of
Enter this information into /etc/passwd and /etc/group files
Assign a password for the account
Set other user account parameters
Create a home directory for the user
Use chown and chgrp to give the new owner ownership
Add the user to any other facilities such as mail, printing and disk quotas
Perform any other site specific initialization tasks.
Test the new account.

4. Defining a new account
Normally, the /etc/passwd file is the master list of information about users. Information about a new user needs to be added to this file.
Each entry in the password file has the following form:
name:coded-passwd:UID:GID:user info:home directory:shellsmith
Smith:/home/smith:/bin/csh

5. Shadow password files
Almost all recent UNIX implementations support shadow password files -files that are protected from all access by non-root users and that store the encrypted password.
crypt - password and data encryption
It is easy to tell when a shadow password file is in use: the password fields in the /etc/passwd are all set to ‘x’. The standard location of the shadow file is /etc/shadow.

6. Automating the Account Creation Process
It is common to create shell scripts to automate the account creation process. There are many variations of the adduser script. The advantage of these tools is that it takes care of remembering a lot of the steps in the process for you.
System V.4 added a user creation command : useradd as well as usermod and userdel. Solaris systems as well as Linux systems with the shadow package have these tools.

7. UNIX Groups Groups may be defined in two ways:
Implicitly, by GID : whenever a new GID appears in the password file, a new group is defined
Explicitly, by name and GID in the /etc/group file
The /etc/group file lists all the system’s named groups:
group_name::GID:additional-users
chem::20:ben,alex,root

8. Standard UNIX Groups root –superuser
daemon -executes system server processes
bin -typically owns the executable files
sys -owns system files
adm -owns the accounting files
uucp -owns the uucp tools and files
mail, news, lp -additional pseudo-users designed to own files and run processes needed by their subsystems
auth -pseudo-users associated with system auditing files
nobody -account used by the NFS protocol

9. Common Startup Files

10. Commonly used commands
useradd
sudo useradd –g 1105 –c “Max R.” max
userdel: removes a user account
usermod: modify a useraccount
sudo usermod –e “12/31/08” max: change the expiration date for the account
groupadd
sudo groupadd –g 1028 pubs
groupdel