From 2e4849b84104b20a275c1ac6cba150c679bc3992 Mon Sep 17 00:00:00 2001
From: jakobrs <jakobrs100@gmail.com>
Date: Sat, 26 Dec 2020 10:55:40 +0100
Subject: [PATCH] installation-cd-base.nix: Add 'live.nixos.passwd' boot option

For interactive SSH access to a system without a (working)
keyboard and monitor, without rebuilding the image itself.
---
 .../administration/boot-problems.section.md     |  6 ++++++
 .../administration/boot-problems.section.xml    | 17 +++++++++++++++++
 .../installer/cd-dvd/installation-cd-base.nix   | 11 +++++++++++
 3 files changed, 34 insertions(+)

diff --git a/nixos/doc/manual/administration/boot-problems.section.md b/nixos/doc/manual/administration/boot-problems.section.md
index eb9209602a32..dee83e7ec225 100644
--- a/nixos/doc/manual/administration/boot-problems.section.md
+++ b/nixos/doc/manual/administration/boot-problems.section.md
@@ -30,6 +30,12 @@ If NixOS fails to boot, there are a number of kernel command line parameters tha
 
 : Make systemd very verbose and send log messages to the console instead of the journal. For more parameters recognised by systemd, see systemd(1).
 
+In addition, these arguments are recognised by the live image only:
+
+`live.nixos.passwd=password`
+
+: Set the password for the `nixos` live user. This can be used for SSH access if there are issues using the terminal.
+
 Notice that for `boot.shell_on_fail`, `boot.debug1`, `boot.debug1devices`, and `boot.debug1mounts`, if you did **not** select "start the new shell as pid 1", and you `exit` from the new shell, boot will proceed normally from the point where it failed, as if you'd chosen "ignore the error and continue".
 
 If no login prompts or X11 login screens appear (e.g. due to hanging dependencies), you can press Alt+ArrowUp. If you’re lucky, this will start rescue mode (described above). (Also note that since most units have a 90-second timeout before systemd gives up on them, the `agetty` login prompts should appear eventually unless something is very wrong.)
diff --git a/nixos/doc/manual/from_md/administration/boot-problems.section.xml b/nixos/doc/manual/from_md/administration/boot-problems.section.xml
index b484d075818a..4ea01e78f32f 100644
--- a/nixos/doc/manual/from_md/administration/boot-problems.section.xml
+++ b/nixos/doc/manual/from_md/administration/boot-problems.section.xml
@@ -106,6 +106,23 @@
       </listitem>
     </varlistentry>
   </variablelist>
+  <para>
+    In addition, these arguments are recognised by the live image only:
+  </para>
+  <variablelist>
+    <varlistentry>
+      <term>
+        <literal>live.nixos.passwd=password</literal>
+      </term>
+      <listitem>
+        <para>
+          Set the password for the <literal>nixos</literal> live user.
+          This can be used for SSH access if there are issues using the
+          terminal.
+        </para>
+      </listitem>
+    </varlistentry>
+  </variablelist>
   <para>
     Notice that for <literal>boot.shell_on_fail</literal>,
     <literal>boot.debug1</literal>,
diff --git a/nixos/modules/installer/cd-dvd/installation-cd-base.nix b/nixos/modules/installer/cd-dvd/installation-cd-base.nix
index 6c7ea293e8ac..aecb65b8c576 100644
--- a/nixos/modules/installer/cd-dvd/installation-cd-base.nix
+++ b/nixos/modules/installer/cd-dvd/installation-cd-base.nix
@@ -30,5 +30,16 @@ with lib;
   # Add Memtest86+ to the CD.
   boot.loader.grub.memtest86.enable = true;
 
+  boot.postBootCommands = ''
+    for o in $(</proc/cmdline); do
+      case "$o" in
+        live.nixos.passwd=*)
+          set -- $(IFS==; echo $o)
+          echo "nixos:$2" | ${pkgs.shadow}/bin/chpasswd
+          ;;
+      esac
+    done
+  '';
+
   system.stateVersion = mkDefault "18.03";
 }