From e0e1338ba48c7d2f64a61eb59daa06a0b78915f3 Mon Sep 17 00:00:00 2001
From: nikstur <nikstur@outlook.com>
Date: Wed, 18 Feb 2026 17:13:38 +0100
Subject: [PATCH 1/2] nixos/tests/systemd: pkgs.systemd ->
 nodes.machine.systemd.package

This makes it easier to tests changes from staging without having to
rebuild the whole world and instead just supplying a new systemd package
via the module system.
---
 nixos/tests/systemd.nix | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/nixos/tests/systemd.nix b/nixos/tests/systemd.nix
index f0bbdef76c61..98cc88a0326f 100644
--- a/nixos/tests/systemd.nix
+++ b/nixos/tests/systemd.nix
@@ -109,10 +109,10 @@
       machine.wait_for_unit("first-boot-complete.target")
 
       machine.succeed(
-        "journalctl --system -o cat --grep 'systemd ${lib.escapeRegex pkgs.systemd.version} running'"
+        "journalctl --system -o cat --grep 'systemd ${lib.escapeRegex nodes.machine.systemd.package.version} running'"
       )
 
-      assert "systemd ${lib.versions.major pkgs.systemd.version} (${pkgs.systemd.version})" in machine.succeed(
+      assert "systemd ${lib.versions.major nodes.machine.systemd.package.version} (${nodes.machine.systemd.package.version})" in machine.succeed(
         "systemctl --version"
       )
 

From ba8e1547428a49d64453905d12a7d812ea53f3c7 Mon Sep 17 00:00:00 2001
From: nikstur <nikstur@outlook.com>
Date: Wed, 18 Feb 2026 17:11:11 +0100
Subject: [PATCH 2/2] nixos/systemd: point various systemd daemons to
 /etc/static

This is done to prepare the removal of
0006-hostnamed-localed-timedated-disable-methods-that-cha.patch from
systemd.

Pointing the daemon to /etc/static will make imperative changes to these
files (e.g. via hostnamectl) fail because systemd cannot edit them.
---
 nixos/modules/system/boot/systemd.nix | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/nixos/modules/system/boot/systemd.nix b/nixos/modules/system/boot/systemd.nix
index 4b7bb1271392..8bfd2a784f47 100644
--- a/nixos/modules/system/boot/systemd.nix
+++ b/nixos/modules/system/boot/systemd.nix
@@ -807,6 +807,31 @@ in
     # Don't bother with certain units in containers.
     systemd.services.systemd-remount-fs.unitConfig.ConditionVirtualization = "!container";
 
+    # When using the classic /etc mechanism, we set certain paths in /etc to
+    # /etc/static so that systemd cannot change them (as they are symlinks to
+    # the read-only Nix Store). This is only done so that these services cannot
+    # change the values. All other parts of systemd should read them from their
+    # canonical locations.
+    #
+    # If you use the overlay mechanism to manage /etc, this is unnecessary
+    # because either the overlay is mutable (and users can legitimately change
+    # values without them being overridden) or it is immutable and systemd will
+    # suggest to only make runtime changes.
+    systemd.services."systemd-localed".environment = lib.mkIf (!config.system.etc.overlay.enable) {
+      SYSTEMD_ETC_LOCALE_CONF = "/etc/static/locale.conf";
+      SYSTEMD_ETC_VCONSOLE_CONF = "/etc/static/vconsole.conf";
+    };
+    systemd.services."systemd-timedated".environment =
+      lib.mkIf (!config.system.etc.overlay.enable && config.time.timeZone != null)
+        {
+          SYSTEMD_ETC_LOCALTIME = "/etc/static/localtime";
+          SYSTEMD_ETC_ADJTIME = "/etc/static/adjtime";
+        };
+    systemd.services."systemd-hostnamed".environment = lib.mkIf (!config.system.etc.overlay.enable) {
+      SYSTEMD_ETC_HOSTNAME = "/etc/static/hostname";
+      SYSTEMD_ETC_MACHINE_INFO = "/etc/static/machine-info";
+    };
+
     # Increase numeric PID range (set directly instead of copying a one-line file from systemd)
     # https://github.com/systemd/systemd/pull/12226
     boot.kernel.sysctl."kernel.pid_max" = mkIf pkgs.stdenv.hostPlatform.is64bit (lib.mkDefault 4194304);