I like to mount /usr read-only for safetly reasons but makewhatis needs to have a writeable /usr/share/man/whatis database. I always thought that it should always be possible to mount /usr read-only (I think that's what the file-system standard says). Should the "whatis" files move to /var/cache/man? Or should /etc/cron.daily/makewhatis check for writeable "whatis" files? Not really a problem but "nice to have"... :-)
I consider this not as an enhancement request, but a real bug. /usr is supposed to be readonly mountable as per FHS. Priority/severity adjusted to normal/normal.
Fixed; the whatis db has been moved to /var/cache/man.