You can check if there's anything in /mnt/flash (or wherever you mounted to), with ls, e.g.

$ ls /mnt/flash.

Hot dang! Lockpicker, you nailed it!

The commands:

mkdir /mnt/flash
and
mount -t vfat /dev/sda1 /mnt/flash

resulted in an icon on my desktop and there are my files on the USB device.

Hot dang!

Many thanks to all who have contributed.

One thing I still don't understand is why use sda1 in the mount command above when Ubuntu has identified the USB device as sda? Please clarify.

You use sda1 because even if it's labelled as sda, it still has a partition on it and you mount filesystems found on partitions. You could repartition it and have two (or more) partitions and then these would be labelled as sda1 and sda2.

To get back to the topic: "how to unmount a device you can't find?"

-> use mount to determine the mounted filesystems:

That should list every mounted filesystem. Then simply use umount to unmount the desired filesystem; if the device you're looking for is not in the list (like sda1), then it's probably not mounted.

This thread seems to have turned into "how to mount" rather than "how to umount"..

My apology as I am coming from Windoze/dos environment, but is this sort of correct?

Ubuntu identified the device and "assigned" it to sda (but it is still not mounted), then the mount command did in fact mount it at sda1 within (or on top of or associated with) sda. i.e., sort of like a subfolder (sda1) under folder sda?

Please correct any misunderstanding or give better analogy as I do want to learn how to do this sort of stuff on my own in future. thanks.

Wooopsie! Just tried to unmount the device before removing it and got:

Error: mount point /mnt/flash is not below /media/

Help!

Bouncer, just saw yours as it posted while I was writing mine above. Thanks for yours and technically you are doubtless correct, but surely it should not be an issue when the obvious answer to the question is to solve another problem first. Then the original issue either then becomes moot, or as in this case, we are now back to the original question.

I used the command:

odyssey@ubuntu:/mnt/flash$ umount sda1 /mnt/flash
umount: sda1 is not mounted (according to mtab)

but it is still mounted, so still can't unmount

for unmounting, just use

umount /mnt/flash
or
umount /dev/sda1

That should do it!

This is beginning to seem like the never-ending saga. Results:

odyssey@ubuntu:/mnt/flash$ sudo umount /mnt/flash
Password:
umount: /mnt/flash: device is busy
umount: /mnt/flash: device is busy

odyssey@ubuntu:/mnt/flash$ sudo umount /dev/sda1
umount: /mnt/flash: device is busy
umount: /mnt/flash: device is busy

Looks like both would have worked if Ubuntu didn't think that the "device is busy" (which AFAIAC, it is not as it has been sitting undisturbed for the last 24 hours.

ran fdisk -l and got

Disk /dev/sda: 64 MB, 64487424 bytes
4 heads, 32 sectors/track, 984 cylinders
Units = cylinders of 128 * 512 = 65536 bytes

Device Boot Start End Blocks Id System
/dev/sda1 * 1 983 62896 6 FAT16

This particular USB drive is a Jumpdrive "Secure" meaning it has some sort of encryption feature (which I have never used), but maybe the "secure" feature runs an application which is constantly polling for input to the drive and marks it for encryption or whatever. This is speculative and maybe irrelevant, but since it is a USB device, it probably runs Linux for any intelligence it needs to provide.

Can anyone suggest a way to determine what is going on that results in the message "device is busy"?

try
umount -l /mnt/flash

that is a lower case L.

Even more. I mounted a second USB drive (without encryption features to create issues) and went to unmount it. Being lazy, I copied the prior command ( sudo umount /dev/sda1 ) and pasted it onto the command line, intending to change the sda1 to sdb1, but apparently the copy picked up the Enter command that was given in the earlier entry and so the command ocurred before I could make the change.

Anyway, much to my surprise, it instantly unmounted the first USB device. Surprising because before the same command resulted in the message in the previous post, but this time it worked.

I then gave the command: "sudo umount /dev/sdb1" and it unmounted the second drive.

So maybe all is OK, but there was some weirdness in that last bit! Anyone have any thoughts on this?

Edit: jstephens, we cross posted. Any additional comments would be welcome.

The device is busy as you're in the folder that the filesystem is mounted to (presumably you have none of the files open). If you change to another directory and try to unmount, it should work.

I understand. Thanks.