How to Add a User to a Group in Linux

Existing User to a Secondary Group

To add an existing user to a secondary group, use the following command:

 usermod -a -G groupname username 

Example:

 usermod -a -G editors john 

Creating a User While Adding it to a Group

You can create a user and add it to a group simultaneously using the useradd command:

 useradd -G groupname username 

Example:

 useradd -G editors jane