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.