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 unmount.
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".
If you found something useful today, please consider a small donation.
Got something to add? Send me email.