How can I linux add user to group under Linux operating system using command line options?

Linux add user to Group

Linux Add a User to Group (or Secondary Group) on Linux

Changing the group of user is associated to is a very easy task, but not
everybody knows the commands, especially to add a user to a secondary group. In
this tutorial we will learn about all user and group related commands.

You can use the useradd or usermod commands to add a user to a group. The useradd command
creates a new user or update default new user information. The usermod command
modifies a user account and it is useful to add user to existing groups. There
are two types of groups under Linux operating systems:
  • Primary user group.
  • Secondary or supplementary user group.

 

All user
account related information are stored in the following files:
  • /etc/passwd – Contains one line for
    each user account.
  • /etc/shadow – Contains the password
    information in encrypted formatfor the system’s accounts and optional account
    aging information.
  • /etc/group – Defines the groups on
    the system.
  • /etc/default/useradd – This file
    contains a value for the default group, if none is specified by the useradd
    command.
  • /etc/login.defs – This file defines
    the site-specific configuration for the shadow password suite stored in
    /etc/shadow file.

 

How to Add a new user to secondary group
In this
example, create a new user called rahul and add it to group called admin. First
login as a root user (make sure group admin exists or not ), :
# grep admin /etc/group

Sample outputs:
[root@linuxelearn
~]# grep admin /etc/group
desktop_admin_r:x:497:
admin:x:507:
[root@linuxelearn
~]#
If you do not see any output then you need to add group admin group using the
groupadd command:
How to Add a New Group    To read Full article about this click here


To add a new group into system, all you need to do is use the groupadd command
like so:#groupadd <groupname>

[root@linuxelearn
~]# groupadd admin

When you create
a group then add that group to user (rahul)
using usermod linux command.
[root@linuxelearn
~]# usermod -G admin rahul
How to add an Existing User to a Group

Frist check
that user rahul exists or not :
# grep ^rahul /etc/passwdNext we are trying to add a user to the group, using this syntax:

#usermod -a -G <groupname> username

For example, to add user rahul to the group admin, use the following command:

[root@linuxelearn
~]# usermod -a -G admin nagios
How can I change a User’s Primary Group

Sometimes you might want to switch out the primary group that a user is
assigned to, which you can do with this usermod
command:#usermod -g <groupname> username

[root@linuxelearn
~]# usermod -g rpgroup nagios

Add a New User and Assign a Group in One Command

Sometimes you might need to add a new user that has access to a particular
resource or directory, like adding a new FTP user. You can do so with the
useradd command:

#useradd -g <groupname> username

Now you are trying to add a new user named pooja to the ftp group:

#useradd -G ftp pooja

[root@linuxelearn
~]# useradd -G ftp pooja

And then you  want to assign a password
for that user, of course:

#passwd Username

 

[root@linuxelearn
~]# passwd pooja
Changing
password for user pooja.
New
password:
BAD
PASSWORD: it is based on a dictionary word
Retype
new password:
passwd:
all authentication tokens updated successfully.
[root@linuxelearn
~]#

Add a User to Multiple Groups

You can easily add a user to more than one group by simply specifying them in a
comma-delimited list, as long as you are assigning the secondary groups:

#usermod -a -G ftp,admin,nagios  <username>

 

[root@linuxelearn
~]# usermod -a -G ftp,admin,nagios pooja
Please note
that capital G (-G) option add user to a list of supplementary groups. Each
group is separated from the next by a comma, with no intervening whitespace. For
example, add user rahul to groups admin, ftp, and nagios.
View a User’s Group Assignments

If you’re trying to figure out a permissions issue, you’ll want to use the id
command to see what groups the user is assigned to:#id <username>

This will display output something like this:

 

[root@linuxelearn
~]# id pooja
uid=503(pooja)
gid=508(pooja) groups=508(pooja),504(ftp),505(nagios),507(admin)
[root@linuxelearn
~]#
You can also use the groups command if you like, though it is the same as using
id -Gn <username>.#groups <username>

 

[root@linuxelearn
~]# groups pooja
pooja
: pooja ram rpgroup admin
[root@linuxelearn
~]#
How to Check a List of All Groups

To view all the groups on the system, you can just use the groups command:#groups

[root@linuxelearn
~]# groups
root
bin daemon sys adm disk wheel
[root@linuxelearn
~]#


How to remove or delete a user from the group

#gpasswd –d <username> <groupname>
#gpasswd –d pooja admin
[root@linuxelearn
~]# gpasswd -d pooja admin
Removing
user pooja from group admin
[root@linuxelearn
~]# grep admin /etc/group
desktop_admin_r:x:497:
admin:x:507:nagios
[root@linuxelearn
~]#
To Add and
remove users and groups you can also use the graphical tool in Linux
#system-config-users
linux add user to group

 

 

This article cover everything you need to know about adding users to groups on Linux.
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