Can't install ubuntu

[Champlin93]

I'm trying to do a standard install of Ubuntu 12.4.1 on my computer after accidentally using Pen Drive Linux's USB Installer on my Ubuntu partition. When trying to install i get an error saying unable to unmount /cdrom device busy.
Upon checking Gparted i see that sda5 (what use to be SWAP space before my accident) is mounted to /cdrom and sda5 and 6(ubuntu partition) are both labeled PENDRIVE and sda5 indeed can't be unmounted.
So i tried the command

sudo umount -l -r -f /cdrom

. No errors were given and upon checking Gparted is is indeed unmounted but i still can't format it to SWAP because the device is still "busy".
Any suggestions?

[Bashing-om]

Champlin93; Hi ! Welcome to the forum .

How about a approach like this:
As a forced umount "umount -f" doesn't resolve anything . The quick fix is a lazy unmount:

umount -l /mnt/deadmount

Another fix for those who do not have mount -l option is smbumount (which worked like a charm for me), I did however first kill the smbmount process manually, not sure it that was needed. -> But:
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a better way is to learn which process uses the device

 umount /dev/sdb1

<substitute your device/partition>
umount: /dev/sdb1: device is busy <-output of command example
umount: /dev/sdb1: device is busy <-output of command example

 fuser -m /dev/sdb1

/dev/sdb1: 3322

3322 is id of the process in this example that uses the device. if you like to know what it is, you may try this:

ps aux | grep 3322

 kill -9 3322

 umount /dev/sdb1

that should work..
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