Fix Virtualbox installation for Docker on macOS

While following a tutorial to install Virtualbox in order to have docker working on macOS, I hit an issue where the docker-machine create command fails with an error that looks like this:

VBoxManage: error: Failed to create the host-only adapter
VBoxManage: error: VBoxNetAdpCtl: Error while adding new interface: failed to open /dev/vboxnetctl: No such file or directory
VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005), component HostNetworkInterfaceWrap, interface IHostNetworkInterface
VBoxManage: error: Context: "RTEXITCODE handleCreate(HandlerArg *)" at line 95 of file VBoxManageHostonly.cpp

If you search on the Web, everybody says you have to open the Security & Privacy settings window and allow the Oracle kernel extensions to run. But I didn’t have it. I tried uninstalling Virtualbox, re-installing through the official website, reboot, uninstall, re-install with brew cask but I always had the issue. Some people reported having a failed Virtualbox installation but mine seemed ok.

I tried the spctl solution but it didn’t change anything.

In the end, I tried this StackOverflow answer:

sudo "/Library/Application Support/VirtualBox/LaunchDaemons/VirtualBoxStartup.sh" restart

It failed, but it told me to check the Security & Privacy setting window. I did, and I had the button everyone was talking about. I enabled the kernel extension, rebooted, and it worked.

Hope this can save some time to anyone having the same issue!