Linux Add Group
Use groupadd or addgroup command to create new user group in Linux system.
$ addgroup GROUP_NAME
Let’s create a group named “testgroup”.
$ addgroup testgroup
Add User to Group
Use usermod command to add user in secondary group.
$ usermod -G testgroup testuser
You can view the group’s names of the user belongs to.
$ groups testuser testuser : testuser testgroup
Assign Group during Create New User
You can also assign the specific group during create creation process. This will also create the primary group
$ useradd -G testgroup rahul