User and group administration in Linux

User and Group Administration:-

There are three type of user account in Red hat Linux

1. Super user or Administrative account
2. Regular user account
3. service account

1. Super User created automatically at the time of installation
2. Regular user Account;

1. Using command line method ‘useradd’ or ‘adduser’ command
2. Graphical method by using Red hat user manager utility

a.

# adduser user_name (Recommended : minimum 6 character used  in password)

# passwd user_name

Example:

#adduser Gaurav

#passwd Gaurav

 Now open the file /etc/passwd to check the entry of user

#vi /etc/passwd

it contain 7 entry of each user

1. Username
2. Password
3. userid
4. groupid
5. blank (User information field ) comment
6. home directory
7. login shell

password entry for each user will be stored in /etc/shadow

# vi /etc/shadow

now in order to check the Userid, Group we use /etc/login.def

# vi /etc/login.def

when any user account is created then user will get userid, groupid automatically from /etc/login.def

5^th field is used for user information or comment

6^th field is used for home directory. When any user is created its default home directory is created inside /home

/home/Gaurav

7^th field is login shell. Default shell for user is /bin/bash

different shells are used

 ksh, sh, csh, tcsh,zsh

shell is an user interface between user and O.S. linux command shell is a prompt that allow us to interact with our system by executing various command.

In order to check the shell available use /etc/shells

# vi /etc/shells

in order to get the information about the group we need /etc/group

#vi /etc/group

it contain four field

1. Group name
2. password
3. GroupId
4. Member of group

# finger : this command is used to get the information about the user

Syntax:

            #finger username

            #finger Gaurav

#id       :           this command is used to get userid, groupid of the user

syntax:

            #id username

            #id Gaurav

Creating Group: 

Syntax:

#groupadd groupname

            #groupadd –g gid groupname

Example:

            #groupadd jeet

Exercise:

Create a user that should have uid=1000 shell=sh description and home directory as /data

Sol:

            #useradd –u 1000 –c Gauravgupta –s /bin/sh –d /data Gaurav

            #passwd Gaurav

Grpahically

System Setting :-> User & Group

OR

#system-config-user

Every user have two group one is elementary group or primary group and secondary group

            -g         :           Primary Group

            -G        :           Secondary Group

Creating Group

#groupadd g1

#groupadd g2

Steps:

1.      adding group to the user

#usermod –g g1 –G g2 Gaurav

2.      To change id of the user

#usermod –u 1001 Gaurav

3.      change comment

#usermod –c Gauravgupta

4.      change home directory

#usermod –d /Gaurav-home Gaurav –m

5.      change shell

#usermod –s /bin/bash Gaurav

6.      change user login name

#usermod –l newname oldname

#usermod –l divakar Gaurav

7.      Change Group name

#groupmod –n newname oldname

#groupmod –n group1 g1

8.      change Group id

#groupmod –g 2005 group1