Make sure the CD is not being used.
Remember, a CD is "being used" if a shell or an application is accessing any of its files or directories. If you are not sure whether you have found all users of a CD (a shell hidden behind a desktop tool might be accessing it), use the fuser command, as described in "How to Find Out If a CD Is Still in Use".
Eject the CD.
# eject cdrom0 |