Filesystems not unmounting: probably because some process is
using it. It might even be you- if you have CD'd there. Something
that sometimes catches folks: you "cd /cdrom" and then perhaps
start another shell. Later on you cd somewhere else, but the shell you
started with is still sitting on /cdrom- and it wll not
On all modern systems, you should have "lsof". A simple "lsof /mnt" (or wherever the cd or disk is) will show you the processes and programs using that.
If you don't have "lsof", use "fuser /mnt" or "fuser /dev/cd0" (note that on Linux these
will produce different results but are equivalent on OSR5 at least)
to find the process and kill it.
A music CD can easily get stuck that way. A mounted DVD/CD image in use
can also be "stuck".