sshd setup for termux

configurations/mobile.nix

@@ -31,6 +31,11 @@ let
       # (default is bashInteractive)
       user.shell = "${pkgs.zsh}/bin/zsh";
 
+      # SSH user (matches `User oqyude` in the client's ~/.ssh/config).
+      # Default is "nix-on-droid"; home stays at the read-only
+      # /data/data/com.termux.nix/files/home either way.
+      user.userName = "oqyude";
+
       # Minimal termux settings (nix-on-droid options only:
       # environment.*, nix.*, time.*, user.*, system.*, android-integration.*)
 

home/termux.nix

@@ -51,11 +51,18 @@
       TUCKR_HOME = "$HOME/Storage/dotfiles";
       EDITOR = "fresh";
     };
-    file.".nanorc".text = ''
+    file = {
+      ".nanorc".text = ''
         set nowrap
         set tabstospaces
         set tabsize 2
       '';
+      # Authorized keys for sshd (see modules/termux/default.nix).
+      # Declarative for now — the Store/.ssh symlink scheme is postponed.
+      ".ssh/authorized_keys".text = ''
+        ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKduJia+unaQQdN6X5syaHvnpIutO+yZwvfiCP4qKQ/P
+      '';
+    };
   };
   programs = {
     # ---- Shell: zsh ----
@@ -68,7 +75,7 @@
         enable = true;
         theme = "robbyrussell";
       };
-      loginExtra = "clear && fastfetch";
+      loginExtra = "clear && fastfetch && cd ~/.config/nix-on-droid";
       initContent = ''
         beet-p() {
           local base="${config.home.homeDirectory}/.config/beets/My"
@@ -99,6 +106,7 @@
         z-proxy = "export ALL_PROXY=socks5://localhost:10808";
         zh-proxy = "export HTTPS_PROXY=http://localhost:10808 && export HTTP_PROXY=http://localhost:10808";
         nix-dir = "cd ~/.config/nix-on-droid";
+        q-ssh = "sshd-start";
 
         # beets
         beet-ima = "beet im ./ -A";

modules/termux/default.nix

@@ -1,9 +1,42 @@
 {
+  config,
   lib,
   pkgs,
   ...
 }:
+let
+  sshdDir = "${config.user.home}/sshd";
+  sshdTmpDir = "${config.user.home}/sshd-tmp";
+  port = 8022;
+in
 {
-  # imports = [
+  # Minimal sshd server for LAN access (e.g. `ssh epral` from other hosts).
-  # ];
+  # nix-on-droid has no systemd: sshd is started manually via `sshd-start`
+  # (or from Termux:Boot / a session). The host key is generated once on the
+  # first activation and kept in ~/sshd (NOT /etc — it is rebuilt on every
+  # activation).
+  environment.etc."ssh/sshd_config".text = ''
+    HostKey ${sshdDir}/ssh_host_ed25519_key
+    Port ${toString port}
+    PasswordAuthentication no
+    AllowUsers ${config.user.userName}
+  '';
+
+  # Generate the host key on first activation (idempotent).
+  build.activation.sshd = ''
+    if [[ ! -d "${sshdDir}" ]]; then
+      $DRY_RUN_CMD rm -rf "${sshdTmpDir}"
+      $DRY_RUN_CMD mkdir -p "${sshdTmpDir}"
+      $VERBOSE_ECHO "Generating sshd host key..."
+      $DRY_RUN_CMD ${pkgs.openssh}/bin/ssh-keygen -t ed25519 -f "${sshdTmpDir}/ssh_host_ed25519_key" -N ""
+      $DRY_RUN_CMD mv "${sshdTmpDir}" "${sshdDir}"
+    fi
+  '';
+
+  environment.packages = [
+    (pkgs.writeScriptBin "sshd-start" ''
+      #!${pkgs.runtimeShell}
+      exec ${pkgs.openssh}/bin/sshd -f /etc/ssh/sshd_config -D "$@"
+    '')
+  ];
 }