Virtualization with vmm: brief history of a failure
I have been wanting to play around with OpenBSD’s native virtualization solution (vmm / vmd) for a while. It is what my VPS host openbsd.amsterdam uses, and I figured having some minimal knowledge of how that works could come in handy in case I mess something up with my virtual machine.
My goal was to set up a FreeBSD VM on an OpenBSD host, preferably relying only official documentation - no DuckDuckGoing.
I am quite a noob when it comes to virtualization. I have used VirtualBox ages ago, and a couple of months back I managed to spin up a qemu VM mostly by copy-pasting commands from the internet. All I know about vmm is that it consists of 3 pieces: vmm(4), vmd(8) and vmctl(8). After a quick scan of the man pages I figured out that vmm is the device driver (whatever that means), vmd is the deamon and vmctl the actual program I want to use to create, start up and shut down the VM.
Keep in mind that this post does not contain instructions to be followed. This is just the cronicle of my first attempt at using this tool.
The first thing I did was heading to the FreeBSD website and download an image of the recently released FreeBSD 14. I started downloading the .iso image, but I soon realized that telling my VM to boot from it would be yet one more thing to figure out. FreeBSD also offers VM images in qcow2 format, the one used by vmm, so I got one of these instead.
Following the examples in vmctl(8), I tried:
$ vmctl start -d frr.qcow2 freebsd
vmctl: connect: /var/run/vmd.sock: No such file or directory
Mmh, ok. There is a missing (socket) file. I don’t know how to create it, and I don’t think I should do it. After a little thinking I realize I should probably start the deamon:
# rcctl -f start vmd
That’s not good, and the error message does not say much. As an aside, I have to point out that this is a constant annoyance I have with OpenBSD: the tools are generally good, the documentation is amazing, but oh god the feedback on error is terrible.
Anyways, after some more man page reading I realize I probably need to install some firmware with fw_update(8) with
It was a bit of a guess game to figure out what driver I had to
install, but I got it on my second attempt (my first try was
The command indeed does something, so I try starting the deamon again:
# rcctl -f start vmd
I took me relatively long to learn that
rcctl has a
to turn on some diagnostics (
-d is for “debug”, but why not a more
-v for “verbose”?). So I try:
# rcctl -f start vmd
vmd_flags empty, using default ><
That is a bit cryptic, but at least it’s something.
Walking in circles
At this point I stopped making progress. It looks like the output above is just generic service-starting stuff, and it has nothing to do with my specific problem.
I tried rebooting, but nothing changed. After reading the man pages more carefully, I thought that maybe enabling the service to start automatically at boot instead starting it manually could do something. It would be weird if it worked, but it was worth a shot. So I enabled it with
# rcctl enable vmd
And rebooted. But still:
I found out about yet another man page, vm.conf(5). I read some of it, but I quickly convinced myself that my error was not related to configuration. It looks like anything you can do from vm.conf you can also do by providing the correct options and arguments to vmctl.
As a last resort, I looked at intro(4), but I did not find anything useful.
I finally gave up and decided to read the official online FAQ. I don’t like relying on them, because it is not something I always have access to - for example if I am travelling and don’t have an internet connection.
The Virtualization section gave me an answer:
A CPU with nested paging support is required to use vmm(4). Support can be
checked by looking at the processor feature flags: SLAT for AMD or EPT for
Intel. In some cases, virtualization capabilities must be manually enabled in
the system's BIOS. Be sure to run the fw_update(8) command after doing so to
get the required vmm-firmware package.
Processor compatibility can be checked with the following command:
$ dmesg | egrep '(VMX/EPT|SVM/RVI)'
And sure enough that command returns nothing on my machine. That is is because I am doing this experiment on my Netbook, and its old Intel Atom N450 CPU does not support virtualization. Bummer.
In the end, I was not able to set up my virtual machine, but that was neither my fault nor OpenBSD’s. At least I did not waste much time with this - I did all of the above in little more than one hour. I guess this is what they call “fail fast?”