how to add user to group on centos

Groups on CentOS

On a CentOS system, groups are used to manage user access to system resources. A group is a collection of users that share common access permissions to resources such as files, directories, and devices.

Groups are created and managed with the groupadd, groupmod, and groupdel commands. Each user on the system is a member of at least one group and can be a member of additional groups. By default, a user is a member of the group with the same name as the user’s username.