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