sudo chown root file.txt, change the owner of
sudo chown root:root file.txt, change the owner and group of
sudo chown :staff file.txt, change the group of
sudo chown -R root:root /var/www, change the owner and group of all files and directories under
sudo chown -h root file.txt, fix the owner of the file pointed to by the symbolic link
sudo in the command line code means to execute the command with administrator privileges.