feat(installer): enhance NixOS installer with SSH access and encryption password input

README.md

@@ -8,7 +8,7 @@ Build a bootable NixOS ISO with the installer preinstalled:
 nix build .#iso
 ```
 
-Write `result/iso/nixos-zfs-installer.iso` to a USB stick (for example with `dd`) or boot it in a VM. The image is the minimal NixOS installation CD with ZFS enabled and `nixos-installer` on `PATH`, so once booted you can run:
+Write `result/iso/nixos-zfs-installer.iso` to a USB stick (for example with `dd`) or boot it in a VM. The image is the minimal NixOS installation CD with ZFS enabled and `nixos-installer` on `PATH`. SSH is enabled and the `nixos` and `root` accounts use the password `nixos`, so you can also run the installer remotely. Once booted:
 
 ```sh
 sudo nixos-installer
@@ -42,7 +42,7 @@ Validate the live environment first with:
 ./nixos-installer --check
 ```
 
-Set `ENCRYPT_KEY` to enable LUKS during install:
+Paste a value into the TUI encryption password field to enable LUKS during install, or set `ENCRYPT_KEY`:
 
 ```sh
 sudo env ENCRYPT_KEY='change-me' ./nixos-installer

python/installer/__main__.py

@@ -6,7 +6,7 @@ import curses
 import logging
 import sys
 from argparse import ArgumentParser
-from os import getenv
+from os import environ, getenv
 from pathlib import Path
 from random import getrandbits
 from subprocess import run
@@ -38,6 +38,29 @@ REQUIRED_COMMANDS = (
 )
 
 
+def configure_terminal() -> None:
+    """Force a terminal type every live system has a terminfo entry for.
+
+    Terminals such as kitty advertise TERM values (xterm-kitty) that live
+    systems have no terminfo entry for, so setupterm fails before the TUI
+    can start.
+    """
+    environ["TERM"] = "xterm-256color"
+
+    if getenv("TERMINFO") or getenv("TERMINFO_DIRS"):
+        return
+    terminfo_fallback_directories = (
+        Path("/run/current-system/sw/share/terminfo"),
+        Path("/usr/share/terminfo"),
+        Path("/etc/terminfo"),
+        Path("/lib/terminfo"),
+    )
+
+    existing_directories = [str(directory) for directory in terminfo_fallback_directories if directory.is_dir()]
+    if existing_directories:
+        environ["TERMINFO_DIRS"] = ":".join(existing_directories)
+
+
 def partition_disk(disk: str, swap_size: int, reserve: int = 0) -> None:
     """Partition a disk.
 
@@ -299,8 +322,8 @@ def installer(
                 check=True,
             )
 
-    # Fixed mount point for the new system; the installer runs as root on a fresh disk
+    # nixos-install rejects mount points under world-writable paths like /tmp
-    mnt_dir = "/tmp/nix_install"  # noqa: S108
+    mnt_dir = "/mnt"
 
     Path(mnt_dir).mkdir(parents=True, exist_ok=True)
 
@@ -336,10 +359,14 @@ def main(argv: Sequence[str] | None = None) -> None:
         logger.info("installer runtime dependencies are available")
         return
 
+    configure_terminal()
     state = curses.wrapper(draw_menu)
 
     encrypt_key = getenv("ENCRYPT_KEY")
 
+    if not encrypt_key:
+        encrypt_key = state.encryption_password
+
     if not state.selected_device_ids:
         logger.error("No disks selected; exiting without installing")
         sys.exit(1)

python/installer/tui.py

@@ -10,6 +10,8 @@ from python.process import run_output
 
 logger = logging.getLogger(__name__)
 
+BYTE_MAX = 255
+
 
 class Cursor:
     """Cursor class."""
@@ -101,6 +103,9 @@ class State:
         self.reserve_size = 0
         self.show_reserve_input = False
 
+        self.encryption_password = None
+        self.show_encryption_password_input = False
+
         self.selected_device_ids: set[str] = set()
 
     def get_selected_devices(self) -> tuple[str, ...]:
@@ -155,7 +160,22 @@ def debug_menu(std_screen: curses.window, key: int) -> None:
         std_screen.addstr(height - 2, i * 3, f"{i}██", curses.color_pair(i))
 
 
-def get_text_input(std_screen: curses.window, prompt: str, y: int, x: int) -> str:
+def draw_input_line(std_screen: curses.window, prompt: str, input_str: str, y: int, x: int, mask: str | None) -> None:
+    """Draw an input line without leaking masked values."""
+    _, width = std_screen.getmaxyx()
+    displayed_input = input_str if mask is None else mask * len(input_str)
+    line = f"{prompt}{displayed_input}"
+    available_width = max(0, width - x - 1)
+
+    std_screen.move(y, x)
+    if available_width > 0:
+        std_screen.addstr(y, x, line[:available_width])
+    std_screen.clrtoeol()
+    std_screen.move(y, min(x + len(line), width - 1))
+    std_screen.refresh()
+
+
+def get_text_input(std_screen: curses.window, prompt: str, y: int, x: int, mask: str | None = None) -> str | None:
     """Get text input.
 
     Args:
@@ -163,27 +183,27 @@ def get_text_input(std_screen: curses.window, prompt: str, y: int, x: int) -> st
         prompt (str): The prompt.
         y (int): The y position.
         x (int): The x position.
+        mask (str | None, optional): The character used to mask displayed input. Defaults to None.
 
     Returns:
-        str: The input string.
+        str | None: The input string, or None if input was cancelled.
     """
     esc_key = 27
-    curses.echo()
+    curses.noecho()
-    std_screen.addstr(y, x, prompt)
     input_str = ""
+    draw_input_line(std_screen, prompt, input_str, y, x, mask)
     while True:
         key = std_screen.getch()
-        if key == ord("\n"):
+        if key in (ord("\n"), ord("\r")):
             break
         if key == esc_key:
-            input_str = ""
+            curses.noecho()
-            break
+            return None
         if key in (curses.KEY_BACKSPACE, ord("\b"), 127):
             input_str = input_str[:-1]
-            std_screen.addstr(y, x + len(prompt), input_str + " ")
+        elif 0 <= key <= BYTE_MAX:
-        else:
             input_str += chr(key)
-        std_screen.refresh()
+        draw_input_line(std_screen, prompt, input_str, y, x, mask)
     curses.noecho()
     return input_str
 
@@ -210,6 +230,9 @@ def swap_size_input(
 
     if state.show_swap_input:
         swap_size_str = get_text_input(std_screen, swap_size_text, swap_offset, 0)
+        if swap_size_str is None:
+            state.show_swap_input = False
+            return state
         try:
             state.swap_size = int(swap_size_str)
             state.show_swap_input = False
@@ -243,6 +266,9 @@ def reserve_size_input(
 
     if state.show_reserve_input:
         reserve_size_str = get_text_input(std_screen, reserve_size_text, reserve_offset, 0)
+        if reserve_size_str is None:
+            state.show_reserve_input = False
+            return state
         try:
             state.reserve_size = int(reserve_size_str)
             state.show_reserve_input = False
@@ -254,6 +280,37 @@ def reserve_size_input(
     return state
 
 
+def encryption_password_input(
+    std_screen: curses.window,
+    state: State,
+    password_offset: int,
+) -> State:
+    """Encryption password input.
+
+    Args:
+        std_screen (curses.window): The curses window.
+        state (State): The state object.
+        password_offset (int): The password offset.
+
+    Returns:
+        State: The updated state object.
+    """
+    password_status = "set" if state.encryption_password else "unset"
+    encryption_label = "Encryption password: "
+    encryption_prompt = "Encryption password (blank disables LUKS): "
+    std_screen.addstr(password_offset, 0, f"{encryption_label}{password_status}")
+    if state.key == ord("\n") and state.cursor.get_y() == password_offset:
+        state.show_encryption_password_input = True
+
+    if state.show_encryption_password_input:
+        password = get_text_input(std_screen, encryption_prompt, password_offset, 0)
+        if password is not None:
+            state.encryption_password = password
+        state.show_encryption_password_input = False
+
+    return state
+
+
 def status_bar(
     std_screen: curses.window,
     cursor: Cursor,
@@ -464,6 +521,11 @@ def draw_menu(std_screen: curses.window) -> State:
             state=state,
             reserve_offset=swap_offset + 1,
         )
+        encryption_password_input(
+            std_screen=std_screen,
+            state=state,
+            password_offset=swap_offset + 2,
+        )
 
         status_bar(std_screen, state.cursor, width, height)
 

systems/iso/default.nix

@@ -24,11 +24,32 @@
 
   networking.hostName = "installer";
 
+  # On flake-built systems <nixpkgs> resolves through the flake registry,
+  # so nixos-install fails without these features enabled.
+  nix.settings.experimental-features = [
+    "flakes"
+    "nix-command"
+  ];
+
   environment.systemPackages = [
     outputs.packages.${pkgs.stdenv.hostPlatform.system}.installer-nixos
   ];
 
+  # Live-media only: sshd is already enabled by the installation profile,
+  # but ssh logins need a non-empty password.
+  users.users = {
+    nixos = {
+      password = "nixos";
+      initialHashedPassword = lib.mkForce null;
+    };
+    root = {
+      password = "nixos";
+      initialHashedPassword = lib.mkForce null;
+    };
+  };
+
   services.getty.helpLine = ''
     Run "sudo nixos-installer" to install NixOS onto a ZFS root pool.
+    SSH is enabled; the "nixos" and "root" passwords are "nixos".
   '';
 }