nixos on m1 vm post

content/posts/nixos-disk-images-m1/index.md

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+date = "2022-06-21"
+draft = false
+path = "/blog/nixos-disk-images-m1"
+tags = ["nix", "nixos"]
+title = "Adventures in building disk images of NixOS virtual machines for M1"
++++
+
+I work in a thoroughly Nix-based environment, and sometimes I need to test
+NixOS things, but I have a Mac at work. So, time to get a NixOS VM going on the
+M1, I guess! This was a partially-planned adventure.
+
+People I know have been saying good things about the (mostly) qemu wrapper
+[UTM] ([also on GitHub here][utm-github]), so that was the tool of choice.
+
+[UTM]: https://mac.getutm.app/
+[utm-github]: https://github.com/utmapp/UTM
+
+I kind of didn't realize there were [normal installer images that would
+absolutely just work][images-lol] (since UTM implements UEFI by default), so I
+tried a more fun option: just build the root filesystem offline and import it.
+
+[images-lol]: https://nixos.wiki/wiki/NixOS_on_ARM/UEFI#Getting_the_installer_image_.28ISO.29
+
+To do this, you will need a Linux machine with Nix and the capacity to execute
+aarch64 binaries, either by emulation with binfmt-misc and qemu-user on Linux,
+or natively because you have an aarch64-linux computer with Nix on it. I have
+the latter because Oracle Cloud [apparently just gives away 24GB memory aarch64
+instances for free][oracle-lol].
+
+[oracle-lol]: https://www.oracle.com/ca-en/cloud/free/#always-free
+
+NixOS has infrastructure for building disk images of systems, so it's more or
+less a case of doing it, with the correct configuration.
+
+The config for the bootloader is also [documented on the NixOS
+wiki here][uefi-bootloader]. The listed config worked for me, which is:
+
+[uefi-bootloader]: https://nixos.wiki/wiki/NixOS_on_ARM/UEFI#Bootloader_configuration
+
+```nix
+{ ... }: {
+  boot.loader.grub = {
+    efiSupport = true;
+    efiInstallAsRemovable = true;
+    device = "nodev";
+  };
+}
+```
+
+Notable things about the hardware UTM configures by default:
+
+* Ethernet: enp0s5, with the host at 192.168.64.1/24 and the guest receiving an
+  IP via DHCP (probably 192.168.64.2)
+* Disk: root on vda2, boot on vda1
+
+It's a QEMU VM so everything is virtio; NixOS provides a configuration to get
+all the necessary modules, which you can import at
+`(modulesPath + "/profiles/qemu-guest.nix")`.
+
+Here's the configuration I used:
+
+{{ codefile(path="./configuration.nix", code_lang="nix", colocated=true, hide=true) }}
+
+Build with:
+
+```
+$ nix-build -I "nixpkgs=channel:nixos-22.05,nixos-config=$(pwd)/configuration.nix" \
+    '<nixpkgs>/nixos' -A config.system.build.image
+```
+
+## Creating a VM
+
+To do this, create a VM, selecting the "Other" type:
+
+{% image(name="./1-os-dialog.png", colocated=true) %}
+Screenshot of the UTM operating system selection dialog, in which macOS, Linux,
+Windows, and Other are listed.
+{% end %}
+
+Then disable ISO boot, since we don't need an installer where we're going.
+
+{% image(name="./2-disable-iso-boot.png", colocated=true) %}
+Dialog in UTM: "disable ISO boot" checkbox checked
+{% end %}
+
+Finish setting up the VM, don't worry about the disk size since we will
+immediately delete it. Select "Open VM Settings" on the summary page so you can
+do that.
+
+{% image(name="./3-open-vm-settings.png", colocated=true) %}
+UTM VM creation summary dialog with "Open VM Settings" box checked
+{% end %}
+
+Then select the disk and delete it:
+
+{% image(name="./4-delete-volume.png", colocated=true) %}
+Screenshot of the VM settings showing the delete button of the disk selected in
+the sidebar.
+{% end %}
+
+Finally, create a new disk, selecting import to get the newly built root
+filesystem image from Nix:
+
+{% image(name="./5-import-image.png", colocated=true) %}
+Screenshot of the "create disk" dialog, with the import button visible.
+{% end %}