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Running Debian 9 inside OpenBSD vmm(4)

At the time of writing, vmm(4) does not emulate CDROM after initial boot. This means you cannot install Debian directly under vmm(4).

We can work around this by doing the initial install under qemu.

Process

Make a disk image with vmctl(8).

$ vmctl create deb9.img -s 50G

(Makes a 50 Gigabyte disk image)

Boot the Debian install CD under qemu with the disk image attached.

$ qemu-system-x86_64 -cdrom debian-9.3.0-amd64-xfce-CD-1.iso -hda deb9.img -boot d -m 3G -net nic -net user

Install Debian as usual.

This will be slow, as qemu is not accelerated on OpenBSD.

Once the install is done, shut down the VM.

Boot the new system under qemu, but without the install CDROM inserted.

$ qemu-system-x86_64 -hda deb9.img -m 3G -net nic -net user

Change the console to the serial line.

At the time of writing, vmm(4) doesn't do VGA emulation, so we have to use the serial line as a console.

Login and edit /etc/default/grub. Add console=ttyS0 to GRUB_CMDLINE_LINUX_DEFAULT. You should then have a line like:

GRUB_CMDLINE_LINUX_DEFAULT="quiet console=ttyS0"

Install the new boot-loader config to the disk, then halt the VM.

# update-grub
...
# halt -p

Boot the VM under vmm(4).

$ doas vmctl start deb9 -d deb9.img -i 1 -L -m 3G -c

Update the networking configuration.

vmm(4) emulates a different kind of network device to qemu, so we have to change the config.

Edit /etc/networks/interfaces and replace all instances of ens3 with enp0s3. You should then have a section like this:

# The primary network interface
allow-hotplug enp0s3
iface enp0s3 inet dhcp<Paste>

Grant the VM network access.

We can use firewall rules to grant the VM access to the internet.

On the OpenBSD host, edit /etc/pf.conf and add a lines like this:

vm_ext=iwm0
vm_dns=8.8.8.8
...
pass out on $vm_ext from 100.64.0.0/10 to any nat-to ($vm_ext)
pass in proto udp from 100.64.0.0/10 to any port domain \
     rdr-to $vm_dns port domain

Change vm_ext and vm_dns to: an interface through which to grant the VM internet access, and a valid DNS server respectively.

The parentheses around $vm_ext causes the NAT rule to lazily look up the address of the interface. This is useful on (e.g.) a laptop, where the IP of (in this case) iwm0 may change as you move networks.

Don't forget that the order of pf(4) rules matters!

Apply the new rules:

# pfctl -f /etc/pf.conf

Then enable ipv4 (or ipv6, if you need it) forwarding:

# sysctl net.inet.ip.forwarding=1
# echo "net.inet.ip.forwarding=1" >> /etc/sysctl.conf

Reboot the VM.

And you are done.

It's probably a good idea to copy the image somewhere safe so you can use as a template for Linux VMs.

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