When I'm developing, I try to continuously deploy to a realistic environment as often as possible. This means a Debian server running a stack as close to production as I can get. Of course, I don't deploy to the actual production servers (a lesson I've learnt many times over), so I virtualise a Debian box and clone package set from the production server. Combined with bridged networking and a quick hosts file change, and I've got a production-equivalent server always available at server.local.
Hence, I use VirtualBox all the time on my Mac, and I've got at least one server instance running all the time. But the Virtualbox.app clutters up the dock, and I really just want the instance available via SSH, I don't care about actually seeing its framebuffer.
Fortunately, you can run headless Virtualbox instances on OSX. It just takes a little extra work. Assuming you installed Virtualbox in the default location, headless Virtualbox binaries live in:
$ ls /Applications/VirtualBox.app/Contents/MacOS | grep "VBoxHeadless"
You can easily run an instance in headless mode by specifying the unique name of the VM on the command line (replace "Debian Server" with the name of your VM):
/Applications/Virtualbox.app/Contents/MacOS/VBoxHeadless --startvm "Debian Server"
Of course, it's a pain to have to start these instances each time you boot the host system, but you can have the VM start on login by adding a LoginHook. Here's how:
sudo defaults write com.apple.loginwindow LoginHook /Applications/Virtualbox.app/Contents/MacOS/VBoxHeadless --startvm "Debian Server"
If you want to stop the VM, just use whatever ACPI shutdown method the guest instance provides (for a Debian server, sudo /sbin/init 0 will suffice), and the VBoxHeadless process will silently quit. If you're virtualising a graphical OS, like Windows, you should probably check the documentation to use with VBoxHeadless; you can easily specify a VRDP address so you can connect to the instance via any RDP client.
Date: 3rd January 2010.
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