Hi Dave,
Here is the OS on my Development Server
[PHP_OS] => Darwin
[PHP_OS_FAMILY] => Darwin
I run cPanel on a VPS with CloudLinux with disk quotas on each of my 60+ client accounts. I will need to migrate to a new server over the next year with Centos being dropped by CloudLinux. Red Hat has really thrown a wrench into things over the past month.
One issue I think to consider is on a shared hosting environment is that there may be disk quotas on the account. You do not have access to the total disk but have limits on the account. I think focusing on the accounts home directory would be the highest you can go in this case. In cpanel we actually have the disk reports available to us already.
The permutations are enormous and the results can be misleading. Not sure the du command is necessary. Certainly no benefit to me as it is although a great idea.
Jeff Shields