Non c'è niente aperto?
[root@localhost My Downloads]# umount -f /mnt/cdrom2
umount2: Device or resource busy
umount: /dev/ide/host0/bus1/target1/lun0/cd: non montato
umount: /mnt/cdrom2: Illegal seek
umount2: Device or resource busy
umount: /mnt/cdrom2: device occupato