You may be faced with a situation in which you must figure out who has permissions to a file or directory and what those permissions are. This sounds simple enough. It really is not as simple as it may sound, here is an example. You view the contents of the /var/www (/var/www/html in CentOS) directory where your web site content is found and you see a directory that looks like this:
Ubuntu
drwxr-xr-x 2 www-data fsmith 4096 2008-05-12 05:19 3qw
CentOS
drwxr-xr-x 2 apache fsmith 4096 2008-05-12 05:19 3qw