unable to unmount volume

[Christopher Lees]

I have had similar problems under Dapper with an external hard disk,
where it claimed that one of the partitions was busy.

I used the lsof command to find out what process was occupying the
partition:

lsof /media/usbdisk

And it showed that Nautilus was the problem. Killing Nautilus (killall
nautilus) and then unmounting always did the trick.

Under Feisty, I was also having problems until I installed the HAL
update.

If updating your system doesn't help, and there are no programs keeping
the drive busy as far as you can determine, then it's fairly safe to
yank out the drive as long as you run the "sync" command first.