Coming from a Linux background, I'm used to a file having an owner, and a owning group. Access permissions can be set separately for owner, group, and others, and that's it.
Now on (NT-based) Windows, it's a bit different, because Windows uses ACLs. That means instead of having three lists of permissions (owner, group, rest), I can have as many lists of permissions as I want.
So far, this makes sense. However, why does Windows still have the notion of a file owner? To me it seems that with ACLs, a "file owner" is no longer needed, because all access can be configured via ACLs.
So why does modern Windows still use file ownership? Where does it make a difference who owns a file? As long as two files have the same ACLs, file ownership should not matter – or does it?
Best Answer
First of all, Linux does have ACLs – POSIX ACLs, which allow setting the permission bits for any number of users and groups. (Patches for RichACL, ACLs very similar to NFSv4 and WinNT, have been submitted repeatedly, but not merged yet.)
Ownership can be used as a sort of safety escape – the owner can always change the object's ACLs, even if the change would be denied otherwise, for example, if someone accidentally removed all ACL entries or denied all changes to everyone. (On Linux only the owner or superuser can change a file's ACLs, since there is no separate "change ACLs" permission.)
Another use of file ownership, on both Windows NT and Linux, is for determining whose quota should the file be counted on, if disk quotas are in use.