User & Group Adminstration


User


1 : Show the details of all users
 user -D                            


2 : To add new user in system 
useradd name 

3 : To delete particuler user from the group 
userdel -r name


4 : usermod command is used for modifying user
eg: If user want to insert comment then
 usermod -c "comment"  user name


5: To set the password on particuler user command will be
passwd username

 


Group Administration

 

1 : To add new group named projectX command will be
groupadd projectX 


2 : To remove group named projectX command wil be
groupdel projectX


3 : To add user in a group 
usermod -G <Group name> <username>


eg: To add username haktuts in a group name called projectX
usermod -G project X haktuts


4 : To add user in a multiple group 
usermod -G <Group name><Group name> <username>


eg: To add username haktuts in a group name called projectX and project Y
           
usermod -G projectX,projectY haktuts


5 : How to provide admin right to specified user in a particuler group
gpasswd -A username groupname 


6 : To add user in a group 
 gpasswd -a username groupname


7 : To remove group named projectX command wil be
 gpasswd -d username groupname 


8 :create new group called abcd           
newgrp abcd   
Note: User can be add in a group via usermod as well as gpasswd  command                                                

 

User and Group Databases file 

 


1 : To check the all set password  go to directory
cat /etc/passwd


2 : To see password which is set in encrypted form
cat /etc/shadow 


3 : To check detail of all the group
cat /etc/group

 



How to Read the passwd file located in etc directory?


username:x:1000:1001::/home/username


username i.e name of user
x   stands for password of user which is masked
1000 is the user id
1001 is the group id
::   user  comment between collens
/home/username  Home directory of user

 

 


How to Read the shadow file located in etc directory?

 

 

username:xyzxyzxyz:11111:0:9999:7:::


username i.e name of user
xyzxyzxyz   stands for password of user which is masked or encrypted form
11111  stands for  No.of days since 1970
0  stands for minimum no of days to change the password
9999  stands for max no of days to change the password
7  stands for warning period
Note Password is encrypted through data encryption standard or MD5 algorithm

 

Types of user 

 


There are two types of user 
1 System users
2 Normal users
id from 0-499 is reserved for system user and 500-60000 is for normal user.