This information has been submitted elsewhere as a 'hack' (to MacFixit.com), but it isn't really. To be honest, I'm not completely sure myself exactly how it's implemented, but I will describe what's necessary.
At the heart of the Unix concept of multiple users (and hence what their permissions are) is the file /etc/passwd. This contains a list of system users, their shells, and their user IDs. The user ID of 0 (zero) represents the system administrator, who has access to all files and directories. Unlike OSes like Lucent's Plan 9 or "trusted" operating systems used in security-intensive military and other situations, the Unix concept of administration has one user who has access to everything, and other users who have limited access to other resources.
Usually, this Unix user ID 0 is referred to as "root" (Windows NT/2000 implements the same concept under the username "Administrator"). If you look at the system files that you're attempting to administer from a Unix console point of view (/MacOS X/Applications/Utilities/Terminal.app), these files are all owned by "root," with only "root" set up to have the priviliges to modify these files.
When you install MacOS X Public Beta, you are prompted to create a username and password; the "user" you create "will have administrative priviliges," you are told. This is true, to an extent - but not fully. You are allowed by the MacOS X GUI to do things that only the Unix "root" can do - but there is no entry in /etc/passwd for your username (although, mysteriously, files can be owned by you).
Although as a BSD sysadmin this shames me to admit, this takes place somewhere in MacOS X that I haven't had time to find out. If I get the chance to search some more and find out how this works, I will post it here (or if someone else already knows, please post
).
Functionally, what happens is that your MacOS X login is translated to having "root" privileges (probably in some MacOS X-specific setup which places you in the same group as root or functionally gives you a User ID of 0. However, you still aren't identified when you log into the terminal environment as "root," which is the user that owns these files.
To change them, use the Terminal app (listed above) and use the "su" command. This will prompt you for a password, which will be the same as that of the "administrative" user you set up originally. From there, you can modify/delete/etc. all the files you want, using Unix shell commands.
