$ umount /cdrom
/dev/sr1: Device is busy
This indicates that some process is still accessing the CD-ROM. Either a user has files open on it, or a program is using it as its current working directory.
To identify the process:
$ fuser -u /cdrom
/cdrom: 348c(bill)
The output shows that process ID 348, owned by user bill, is accessing /cdrom.
If you need to terminate all processes using the mount point:
$ fuser -k /cdrom
/cdrom: 348c
No automatic removal. Please use umount /cdrom
Now try unmounting again:
$ umount /cdrom
The unmount should now succeed.
As root, you can forcefully terminate all processes accessing files within the mount point:
$ fuser -k /cdrom/*.*
If local directories or mounted partitions are affected (for example /win/d):
$ fuser -k /win/d/*.*
This will terminate all processes currently accessing files within that path.