Show user list
Show user’s group
Assign user to a primary group (Require re-login to apply the new group)
usermod -g GROUP_NAME USER_NAME
Assign user to a secondary group
usermod -a -G GROUP_NAME USER_NAME
Turn on setgid bit (all new files and subdirectories created within the current directory inherit the group ID of the directory, rather than the primary group ID of the user who created the file)
chmod g+s .
Turn off setgid bit
chmod g-s .
Check if setgid is on
(If it is on, the group permission will become rws instead of rwx)