How to add an existing user into a group in Linux using command line options? ~ How can I add a user to a group under Linux operating system using command line options?

Adding user to a Group

Add a User to a 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/passwd

Next 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

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