I occasionally come across a situation where I am trying to unmount a device (umount /mnt/harddrive ) for whatever reason and it refuses to unmount because it claims to be in use:

umount: /path: device is busy.

Usually this is after I think I’m sure that no programs are using the device or that no files are open on the device. So how do we find out what is using it? Easy – with this one simple command…

lsof | grep /mnt/harddrive

It then returns the details of what is actually keeping your device active. For me it was a SAMBA share and a calibre ebook library.

You can kill these things with a simply kill PID