feat: custom kexec installer for headless install on read-only-root (ZimaOS)

- add nixos-images input; nixosConfigurations.kexec bakes in the ssh login key
- build via config.system.build.kexecInstallerTarball
- deploy: ./deploy kexec <host> streams the installer to /tmp and kexecs
- works around ZimaOS RO root where nixos-anywhere ssh-copy-id fails

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

deploy

@@ -1,8 +1,12 @@
 #!/usr/bin/env bash
 # Deploy the jupiter NixOS config.
 #
-#   ./deploy install <ip>     first install onto a fresh box (nixos-anywhere).
+#   ./deploy kexec   <host>   headless-only: for a read-only-root box (ZimaOS)
-#                             Wipes the OS disk. Ships the sops host key.
+#                             where nixos-anywhere can't ssh-copy-id. Uploads a
+#                             kexec installer (our SSH key baked in) to /tmp and
+#                             boots into it. Then run `install`.
+#   ./deploy install <ip>     first install onto a fresh box / running installer
+#                             (nixos-anywhere). Wipes the OS disk. Ships host key.
 #   ./deploy [switch] [host]  rebuild + activate on a running jupiter (default).
 #   ./deploy boot   [host]    stage for next boot, don't activate now.
 #   ./deploy test   [host]    activate without adding a boot entry.
@@ -18,11 +22,30 @@ HOSTKEY="$HOME/.config/homelab/jupiter/ssh_host_ed25519_key"
 
 cmd="${1:-switch}"
 case "$cmd" in
-  switch|boot|test|install) shift || true ;;
+  switch|boot|test|install|kexec) shift || true ;;
   *) cmd="switch" ;;
 esac
 
 case "$cmd" in
+  kexec)
+    host="${1:-}"
+    [ -n "$host" ] || { echo "usage: ./deploy kexec <ip-or-host>" >&2; exit 1; }
+
+    echo ">> building kexec installer (SSH key baked in)"
+    nix build .#nixosConfigurations.kexec.config.system.build.kexecInstallerTarball \
+      -o result-kexec
+    tb="$(ls result-kexec/*.tar.gz | head -1)"
+
+    echo ">> streaming installer to root@$host and kexec-ing  (enter root password)"
+    echo "   Extracted to /tmp (tmpfs); no compressed copy stored. SSH drops as"
+    echo "   the box jumps into the RAM installer. Disks are untouched."
+    # Stream the tarball straight into remote tar to avoid a second 522MB copy.
+    ssh "root@$host" 'mkdir -p /tmp/k && tar -C /tmp/k -xzf - && /tmp/k/kexec/run' < "$tb" || true
+
+    echo ">> box is kexec-ing. Wait ~1-2 min for the installer + network, then:"
+    echo "   ./deploy install $host"
+    ;;
+
   install)
     host="${1:-}"
     [ -n "$host" ] || { echo "usage: ./deploy install <ip-or-host>" >&2; exit 1; }

flake.lock

@@ -20,6 +20,59 @@
         "type": "github"
       }
     },
+    "nixos-images": {
+      "inputs": {
+        "nixos-stable": "nixos-stable",
+        "nixos-unstable": "nixos-unstable"
+      },
+      "locked": {
+        "lastModified": 1783593136,
+        "narHash": "sha256-zy5an02BdZ65OgVKdRkz2TpbdBrsW+uQD7AA2wLuiTM=",
+        "owner": "nix-community",
+        "repo": "nixos-images",
+        "rev": "803f28511c7d5f39f2537c342122fd94b8e1d519",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "nixos-images",
+        "type": "github"
+      }
+    },
+    "nixos-stable": {
+      "locked": {
+        "lastModified": 1783389287,
+        "narHash": "sha256-0xIy4dVLqq47rA+mRy0hXDfjhQd4E5PoIns/RmB7nR4=",
+        "ref": "nixos-26.05",
+        "rev": "0ad6f47ea4fe188f4bc8f0380f93ae8523337c6c",
+        "shallow": true,
+        "type": "git",
+        "url": "https://github.com/NixOS/nixpkgs"
+      },
+      "original": {
+        "ref": "nixos-26.05",
+        "shallow": true,
+        "type": "git",
+        "url": "https://github.com/NixOS/nixpkgs"
+      }
+    },
+    "nixos-unstable": {
+      "locked": {
+        "lastModified": 1782175435,
+        "narHash": "sha256-EMzXKmnOtBQ2MnvpiNOm7E+kOMvdPrIKaeg52Tip2Uk=",
+        "ref": "nixpkgs-unstable",
+        "rev": "89570f24e97e614aa34aa9ab1c927b6578a43775",
+        "shallow": true,
+        "type": "git",
+        "url": "https://github.com/NixOS/nixpkgs"
+      },
+      "original": {
+        "ref": "nixpkgs-unstable",
+        "shallow": true,
+        "type": "git",
+        "url": "https://github.com/NixOS/nixpkgs"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1783703440,
@@ -39,6 +92,7 @@
     "root": {
       "inputs": {
         "disko": "disko",
+        "nixos-images": "nixos-images",
         "nixpkgs": "nixpkgs",
         "sops-nix": "sops-nix"
       }

flake.nix

@@ -11,9 +11,13 @@
       url = "github:Mic92/sops-nix";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    nixos-images = {
+      url = "github:nix-community/nixos-images";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
-  outputs = { self, nixpkgs, disko, sops-nix, ... }@inputs:
+  outputs = { self, nixpkgs, disko, sops-nix, nixos-images, ... }@inputs:
     let
       system = "x86_64-linux";
     in
@@ -39,6 +43,23 @@
           specialArgs = { inherit inputs; };
           modules = [ ./jupiter/vm.nix ];
         };
+
+        # Custom kexec installer with our SSH key baked in, for headless install
+        # onto a box with a read-only root (ZimaOS) where nixos-anywhere can't
+        # ssh-copy-id. Build the tarball:
+        #   nix build .#nixosConfigurations.kexec.config.system.build.kexecInstallerTarball
+        # then scp it to the target's writable /tmp and run kexec/run (see README).
+        kexec = nixpkgs.lib.nixosSystem {
+          inherit system;
+          modules = [
+            nixos-images.nixosModules.kexec-installer
+            ({ ... }: {
+              users.users.root.openssh.authorizedKeys.keys = [
+                "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGZpkPVhzi1zG5JI9hWyUgdyvNIQbp4ts4jw3idpMhhN erik@laptop"
+              ];
+            })
+          ];
+        };
       };
     };
 }