Remove kernel module on Linux – failed

When I was reinstalling Virtual Box I stumbled on an error with unloading module vboxnetflt.

I tried several methods to remove that module manually:

root@server:~# /etc/init.d/vboxdrv setup
* Stopping VirtualBox kernel modules
* Cannot unload module vboxnetflt
root@server:~# modprobe -r vboxnetflt
FATAL: Module vboxnetflt not found.
root@server:~# rmmod vboxnetflt
ERROR: Module vboxnetflt is in use

I had no success even with force:
root@server:~# rmmod --force vboxnetflt
ERROR: Removing 'vboxnetflt': Resource temporarily unavailable

I turned out we had a lost vbox process VBoxHeadless hanging. After killing it everything went fine. So if rmmod --force did not work for you – look for potential processes keeping handles to the module.