I'm using systemd-boot (no grub) with UEFI, and for this it is enought to have single /boot with ESP like this

          type = "gpt";
          partitions = {
            ESP = {
              type = "EF00";
              size = "2G";
              content = {
                type = "filesystem";
                format = "vfat";
                mountpoint = "/boot";
              };
            };

For those using disko for vm’s disk sizes…

I wonder. Are you declaratively setting your vm .qcow2 for example, from the host system? Or from inside the vm.

this seems to be enough to get it to work

          esp = {
            size = "1024M";
            type = "EF00";
            content = {
              format = "vfat";
              type = "filesystem";
              mountpoint = "/boot";
              mountOptions = [ "umask=0077" ];
              postMountHook =
                let
                  configTxt = pkgs.writeText "config.txt" ''
                    [pi4]
                    kernel=u-boot-rpi4.bin
                    disable_overscan=1
                    enable_gic=1
                    arm_boost=1

                    [all]
                    avoid_warnings=1
                    enable_uart=1
                    arm_64bit=1
                  '';
                in
                toString (
                  pkgs.writeScript "postMountHook.sh" ''
                    (cd ${pkgs.raspberrypifw}/share/raspberrypi/boot && cp bootcode.bin fixup4.dat start4.elf bcm2711-*.dtb /mnt/boot/)
                    cp ${pkgs.ubootRaspberryPi4_64bit}/u-boot.bin /mnt/boot/u-boot-rpi4.bin
                    cp ${configTxt} /mnt/boot/config.txt
                  ''
                );
            };
          };

proper hack, works without disko too

{
  config,
  pkgs,
  lib,
  ...
}:

let
  installBootLoader =
    (import (pkgs.path + "/nixos/modules/system/boot/loader/generic-extlinux-compatible") {
      inherit config lib pkgs;
    }).config.content.system.build.installBootLoader;

  populateFirmware =
    (import (pkgs.path + "/nixos/modules/installer/sd-card/sd-image-aarch64.nix") {
      inherit config lib pkgs;
    }).sdImage.populateFirmwareCommands;

  installCmd = pkgs.writeShellScript "populate-boot.sh" ''
    set -e && export PATH=${pkgs.coreutils}/bin:$PATH
    ${installBootLoader} "$@"

    ln -s "/boot" "$NIX_BUILD_TOP/firmware" 
    cd "$NIX_BUILD_TOP" && ${populateFirmware} 
    echo "include usercfg.txt" >> /boot/config.txt
  '';
in
{
  system.build.installBootLoader = lib.mkForce installCmd;
}

proper hack, works without disko too

{
  config,
  pkgs,
  lib,
  ...
}:

let
  installBootLoader =
    (import (pkgs.path + "/nixos/modules/system/boot/loader/generic-extlinux-compatible") {
      inherit config lib pkgs;
    }).config.content.system.build.installBootLoader;

  populateFirmware =
    (import (pkgs.path + "/nixos/modules/installer/sd-card/sd-image-aarch64.nix") {
      inherit config lib pkgs;
    }).sdImage.populateFirmwareCommands;

  installCmd = pkgs.writeShellScript "populate-boot.sh" ''
    set -e && export PATH=${pkgs.coreutils}/bin:$PATH
    ${installBootLoader} "$@"

    ln -s "/boot" "$NIX_BUILD_TOP/firmware" 
    cd "$NIX_BUILD_TOP" && ${populateFirmware} 
    echo "include usercfg.txt" >> /boot/config.txt
  '';
in
{
  system.build.installBootLoader = lib.mkForce installCmd;
}

Couple of questions about NixOS live USBs:

I want to partition my 64 GB USB flash drive into two partitions (FAT32 live USB + ext4 storage), so I used the following disko config:

let
  usb = "/dev/disk/by-id/usb-USB_SanDisk_3.2Gen1_0401a943ae4197a38a6f9070194e9ea2b3fb8dbb7997e05ed1b197c0e28946be4b8f000000000000000000001cf4be6800926418a955810751ab6336-0:0";
in {
  disko.devices = {
    disk = {
      live = {
        type = "disk";
        device = usb;
        content = {
          type = "gpt";
          partitions = {
            ESP = {
              type = "EF00";
              device = "${usb}-part1";
              priority = 0;
              size = "8192M";
              content = {
                type = "filesystem";
                format = "vfat";
              };
            };
            storage = {
              device = "${usb}-part2";
              priority = 1;
              size = "100%";
              content = {
                type = "filesystem";
                format = "ext4";
              };
            };
          };
        };
      };
    };
  };
}

I then copied over the files from the (minimal, non-graphical) NixOS live ISO into partition 1, hoping that the instructions on the Arch wiki would generalize to NixOS, but then my live ISO gets stuck with the following error message:

[...]
Timed out waiting for device /dev/root, trying to mount anyway
mounting /dev/root on /iso...
mount: mounting /dev/root on /mnt-root/iso failed: No such file or directory

An error occurred [...]

How can I use my USB flash drive as both a live USB and as a storage device? I found this relevant Discourse link but there was no resolution to the problem there.

I realize this might not be the best place to ask this, but I figured that folks here would have expertise configuring boot partitions correctly.

Couple of questions about NixOS live USBs:

I want to partition my 64 GB USB flash drive into two partitions (FAT32 live USB + ext4 storage), so I used the following disko config:

let
  usb = "/dev/disk/by-id/usb-USB_SanDisk_3.2Gen1_0401a943ae4197a38a6f9070194e9ea2b3fb8dbb7997e05ed1b197c0e28946be4b8f000000000000000000001cf4be6800926418a955810751ab6336-0:0";
in {
  disko.devices = {
    disk = {
      live = {
        type = "disk";
        device = usb;
        content = {
          type = "gpt";
          partitions = {
            ESP = {
              type = "EF00";
              device = "${usb}-part1";
              priority = 0;
              size = "8192M";
              content = {
                type = "filesystem";
                format = "vfat";
              };
            };
            storage = {
              device = "${usb}-part2";
              priority = 1;
              size = "100%";
              content = {
                type = "filesystem";
                format = "ext4";
              };
            };
          };
        };
      };
    };
  };
}

I then copied over the files from the (minimal, non-graphical) NixOS live ISO into partition 1, hoping that the instructions on the Arch wiki would generalize to NixOS, but then my live ISO gets stuck with the following error message:

[...]
Timed out waiting for device /dev/root, trying to mount anyway
mounting /dev/root on /iso...
mount: mounting /dev/root on /mnt-root/iso failed: No such file or directory

An error occurred [...]

How can I use my USB flash drive as both a live USB and as a storage device? I found this relevant Discourse link but there was no resolution to the problem there.

I realize this might not be the best place to ask this, but I figured that folks here would have expertise configuring boot partitions correctly.

For reference, the NixOS manual says I should dd the ISO to the disk directly: sudo dd if=<path-to-image> of=/dev/sdX bs=4M conv=fsync