su segfault (core dump) problem.

[Greg Lindahl]

> anything that you are running that is (for example) opening a file in
> /usr (presumed shared and static) instead of /var (presumed local and
> volatile) is a candidate for such a problem if node a reads from and
> writes to the file while node b is doing the same thing.  A shared /dev
> can be equally evil the same way.

If you expect /usr to be invariant, mount it read-only. You'll find out soon
enough all the things which write to it!

-- g