Users and groups are used on GNU/Linux for access control that is, to control access to the system's files, directories, and peripherals. Linux offers relatively simple/coarse access control mechanisms by default.

1. By – Varnnit Jain
9990888972
Users And Groups In RHEL

2. Users
 Every person that logs into the computer is considered as a
user.
 Every user is assigned a unique user ID number (UID).
UID 0 identifies root.
 User acccounts usually starts at UID 500.
 1-499 UID is reserved for the system users.
 Whenever you create any user in Linux It belongs to their
own group.
 User names and UIDs are stored in /etc/passwd.
 Users are assigned a home directory ( /home/username) and
a program that is run when they log in. (Usually a shell)

3. USERS
 Users have full access to their directories.
 User cannot read, write or execute each other
files without permission.

4. GROUP
 A group is a collection of users which make easy
for administration to perform the task of
administration level.
 When they need to apply permissions and
restrictions with the same level to many users ,
the such permissions an restrictions can be
applied to related groups.
 Users are assigned to groups .
 Every user is a member of at least one group and
possibly more.
 Each group is assigned a unique group ID
number (GID).

5. GROUP
 Each group is given their own private group
(primary group, usually the same name of the
user).
 Users can be added to other groups.
 User’s primary group is defined in the
/etc/passwd file.
 User’s secondary group is defined in the
/etc/group file.
 All users in a group can share files that belong to
that user.

6. In Command Line
 #adduser username : Create a new user.
 #passwd username : Change/set
password for user.
 #groupadd groupname: create a new group.
 #gpasswd groupname : Set Group Password.
 #usermod –g groupname user name ,:Change
the primary group of the user
 #usermod –G groupname username : Create a
secondary group for a user.
 #usermod –a G groupname username : join user
in multiple secondary group but more steps are
required.

7.  #usermod –l username : Lock user.
 #usermod --lock username : lock user.
 #passwd -S username : Want to see if the user is
ocked or not.
 #usermod –U username : Unlock user.
 #usermod –unlock username : Unock user.
 #userdel –r username : Delete user wih its
directory.
 #usermod –l newname oldname : Rename the user.
 #gpasswd –a username groupname : Add user to
groups.
 #gpasswd –d username groupname : Remove user
from group.

8. Example
1. #adduser varnnit
2. #passwd varnnit.
2. #groupadd varnnitjain ; gpasswd varnnitjain

9. 3. A new user has been added.

10. 4. #usermod –aG group_name user_name This command is
used to add a user to a secondary group.

11. .
5. #usermod –L username
6. #passwd –S username
7. #usermod –U username

12. 8. #userdel –r username

13. 9. #usermod –l new_name old_name

14. 10. Usermod –e expire_date user_name
11. #gpasswd –a user_name group_name