Sometimes when I want to umount a device, e.g.sudo umount /dev/loop0I will get the messageumount: /mnt: device is busy.        (In some cases useful info about processes that use         the device is found by lsof(8) or fuser(1))I usually solve this issue by closing a console window (in my case xfce4-terminal) and then umount.What does this problem mean? Is there some smarter solution?
umount - device is busy
mount
It means that some process has a working directory or an open file handle underneath the mount point. The best thing to do is to end the offending process, change its working directory or close the file handle before unmounting.There is an alternative on Linux though. Using umount -l calls a lazy unmount. The filesystem will still be mounted but you won't be able to see or use it, except for processes that are already using it. When the offending program exits (through whatever means) the system will finish unmounting the filesystem.