configuration.nix

{ ... }: {

    boot.initrd.postDeviceCommands = ''
      for o in $(cat /proc/cmdline); do
          case $o in
              nfsnixstore=*)
                  params="''${o#nfsnixstore=}"
                  nfsnixstore_mount=/nfs-nix-store
                  nfsnixstore_export=$(echo $params | cut -d, -f1)
                  nfsnixstore_options=$(echo $params | cut -d, -f2-)
                  echo "mounting $nfsnixstore_export with $nfsnixstore_options on $nfsnixstore_mount..."
                  mkdir -p $nfsnixstore_mount
                  mount -t nfs -o $nfsnixstore_options $nfsnixstore_export $nfsnixstore_mount
                  ;;
          esac
      done
    '';

    fileSystems."/" = {
      fsType = "tmpfs";
      options = [ "mode=0755" ];
    };

    fileSystems."/nix/.ro-store" = {
      device = "../nfs-nix-store";
      options = [ "bind" ];
      neededForBoot = true;
    };

    fileSystems."/nix/.rw-store" = {
      fsType = "tmpfs";
      options = [ "mode=0755" ];
      neededForBoot = true;
    };

    fileSystems."/nix/store" = {
      fsType = "overlay";
      device = "overlay";
      options = [
        "lowerdir=/nix/.ro-store"
        "upperdir=/nix/.rw-store/store"
        "workdir=/nix/.rw-store/work"
      ];
    };


}

list-dependencies-dhcpcd.log

$ systemctl list-dependencies dhcpcd.service
dhcpcd.service
● ├─system.slice
● ├─systemd-udev-settle.service
● ├─network.target
● │ ├─network-local-commands.service
● │ └─network-interfaces.target
● └─sysinit.target
●   ├─dev-hugepages.mount
●   ├─dev-mqueue.mount
●   ├─kmod-static-nodes.service
●   ├─sys-fs-fuse-connections.mount
●   ├─sys-kernel-config.mount
●   ├─sys-kernel-debug.mount
●   ├─systemd-ask-password-console.path
●   ├─systemd-journal-catalog-update.service
●   ├─systemd-journal-flush.service
●   ├─systemd-journald.service
●   ├─systemd-modules-load.service
●   ├─systemd-random-seed.service
●   ├─systemd-sysctl.service
●   ├─systemd-timesyncd.service
●   ├─systemd-tmpfiles-setup.service
●   ├─systemd-udev-trigger.service
●   ├─systemd-udevd.service
●   ├─systemd-update-done.service
●   ├─systemd-update-utmp.service
●   ├─local-fs.target
●   │ ├─-.mount
●   │ ├─nix-.ro\x2dstore.mount
●   │ ├─nix-.rw\x2dstore.mount
●   │ ├─nix-store.mount
●   │ └─systemd-remount-fs.service
●   └─swap.target

list-dependencies-nix-ro-store.log

$ systemctl list-dependencies nix-.ro\\x2dstore.mount
nix-.ro\x2dstore.mount
● ├─-.mount
● ├─system.slice
● └─network-online.target
●   └─dhcpcd.service

systemctl-cat-nix-ro-store.log

$ systemctl cat nix-.ro\\x2dstore.mount
# /run/systemd/generator/nix-.ro\x2dstore.mount
# Automatically generated by systemd-fstab-generator

[Unit]
Documentation=man:fstab(5) man:systemd-fstab-generator(8)
SourcePath=/etc/fstab
Before=local-fs.target

[Mount]
Where=/nix/.ro-store
What=../nfs-nix-store
Options=bind