admin user use sudo can be do:（拥有sudo权限应该做什么？）
1: add <username> to <groupname> group
sudo gpasswd -a <username> <groupname>
2: remove <username> from <groupname> group
sudo gpasswd -d <username> <groupname>
3: change owner of directory
sudo chown -R <username> /home/bee/test
normal user can be do direct:（普通用户权限可以做什么操作？）
It is important to set "umask 066" before operating files
"umask 066" means remove read & write, just keep execute.
1: change the group ownership of a file or directory
chgrp <groupname> ~/test
2: change ACLs of a file or directory
open or close read & write for group
chmod -R g+rw ~/test
chmod -R g-rw ~/test
open or close read & write for other
chmod -R o+r ~/test
chmod -R o-r ~/test