Why aren't 16-bit UIDs enough?

I would like to make the point:

Linux needs to get support for UIDs >16 bits.

Some people have argued that you shouldn't have 65,536 people sharing the same machine. This may be true regarding the typical machine; however, the point is that it is often desirable to share UIDs across many machines and when you have >65,536 people on your network, 16-bit UIDs aren't enough.
This is the situation at the University of Michigan. We have about 110,000 users in a shared Unix environment; we use AFS to store all home directories. We use a shared passwd file on thousands of Unix machines all over campus so people can log in anywhere and there really is no way to "fudge" this setup with 16-bit UIDs.

But nonetheless we'd like to use Linux...

Perhaps arguably, the whole concept of "user IDs" may be what's outlasted its usefulness here, not choosing a particular size for UID. However, transcending the traditional Unix UID system is certainly beyond my scope at the moment and it's much easier to just change everything to 32-bits for now :)

Now, here are some non-rational arguments:

- 16 bits are so "MS-DOS"!!
- I want a Linux box with 100,000 people logged into it simultaneously
and, of course,
- HP, IBM, Sun, SGI, ..., *BSD have 32-bit UIDs!!!!!

- Chris Wing - wingc@engin.umich.edu - 12/1/1998