Coexisting VirtualBox and VMWare Fusion on macOS

Both VirtualBox and VMWare Fusion are neat virtualization tools. I use Fusion for most day to day work - it’s served me well for a long time and I have a significant stash of useful machines in it. But sometimes I also need to use VirtualBox, typically for working with Vagrant. The problem is that the two of them don’t get along very well…

When you install VirtualBox and then try to start a VM in Fusion you’ll see something like this:

Could not open /dev/vmmon: No such file or directory.

Googling this will lead you to the answer that VirtualBox and Fusion are incompatible and that you need to uninstall VirtualBox. I didn’t find a better solution documented, so here it is in blog post form now instead.

The incompatibility is between the kernel extensions used by each. I think Fusion is the more well behaved in this respect - it loads and unloads its kernel extensions as it starts and stops. This means that when it’s not running, VirtualBox can run. But VirtualBox doesn’t do this. It loads kernel extensions at installation time (and presumably on boot thereafter). You can see these in kextstat:

jb@unu:~ $ kextstat | grep virtualbox
  226    3 0xffffff7f83d52000 0x61000    0x61000    org.virtualbox.kext.VBoxDrv (5.1.22) 93316754-E074-3CE2-9464-DDA4356FF02E <7 5 4 3 1>
  228    0 0xffffff7f83bd8000 0x8000     0x8000     org.virtualbox.kext.VBoxUSB (5.1.22) D956DCFA-4E4F-320A-BEBC-E4823501B1FF <227 226 41 7 5 4 3 1>
  230    0 0xffffff7f83c22000 0x6000     0x6000     org.virtualbox.kext.VBoxNetAdp (5.1.22) 4A6C39E1-5D90-3E34-9673-57B0DD779CD7 <226 5 4 1>
  231    0 0xffffff7f83c28000 0x5000     0x5000     org.virtualbox.kext.VBoxNetFlt (5.1.22) 446923A0-E855-3E75-9173-66FA4CE2474A <226 7 5 4 3 1>

We can work around this with a couple of scripts so that we can at least switch between the two manually. To be able to run Fusion we need to unload the VirtualBox kexts:

for id in VBoxNetAdp VBoxNetFlt VBoxUSB VBoxDrv; do
    kextunload -b "org.virtualbox.kext.$id"

Save that as ~/bin/unload-vbox or something and run it as sudo unload-vbox. When we’re not running Fusion we can load the VirtualBox kexts and VirtualBox will work fine:

for id in VBoxDrv VBoxUSB VBoxNetFlt VBoxNetAdp; do
    kextload -r "/Library/Application Support/VirtualBox" \
     "/Library/Application Support/VirtualBox/$id.kext"

In the end, some sort of coexistence is achieved. :)


Jakob is a Senior Technical Architect at Kastelo Inc. and works with development, networking, and maintaining Syncthing.

We're based in Malmö, Sweden — probably the best place to be in the Nordics.

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