From ed5f0fbfcd89b6109c48e2c8f1909d83b08ab33c Mon Sep 17 00:00:00 2001
From: WilliButz <willibutz@posteo.de>
Date: Mon, 23 Jun 2025 20:08:28 +0200
Subject: [PATCH] nixos/repart-image: don't pass seed when it's null, update
 documentation

From systemd-repart(8):

If not specified it is attempted to read the machine ID from the host
(or more precisely, the root directory configured via --root=) and use
it as seed instead, falling back to a randomized seed otherwise. Use
--seed=random to force a randomized seed.

The option documentation now suggests the special value "random", for
a random seed rather than relying on the implicit fact that there is
no machine ID available in the build sandbox, causing repart to fallback
on generating a random seed.

Fixes #419331
---
 nixos/modules/image/repart-image.nix | 4 +++-
 nixos/modules/image/repart.nix       | 3 ++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/nixos/modules/image/repart-image.nix b/nixos/modules/image/repart-image.nix
index e62db75caf8f..49087d4786c5 100644
--- a/nixos/modules/image/repart-image.nix
+++ b/nixos/modules/image/repart-image.nix
@@ -173,11 +173,13 @@ stdenvNoCC.mkDerivation (
         "--architecture=${systemdArch}"
         "--dry-run=no"
         "--size=auto"
-        "--seed=${seed}"
         "--definitions=${finalAttrs.finalRepartDefinitions}"
         "--split=${lib.boolToString split}"
         "--json=pretty"
       ]
+      ++ lib.optionals (seed != null) [
+        "--seed=${seed}"
+      ]
       ++ lib.optionals createEmpty [
         "--empty=create"
       ]
diff --git a/nixos/modules/image/repart.nix b/nixos/modules/image/repart.nix
index 13c90aa9ab7a..a44a2e5f9ea3 100644
--- a/nixos/modules/image/repart.nix
+++ b/nixos/modules/image/repart.nix
@@ -161,8 +161,9 @@ in
       # Generated with `uuidgen`. Random but fixed to improve reproducibility.
       default = "0867da16-f251-457d-a9e8-c31f9a3c220b";
       description = ''
-        A UUID to use as a seed. You can set this to `null` to explicitly
+        A UUID to use as a seed. You can set this to `random` to explicitly
         randomize the partition UUIDs.
+        See {manpage}`systemd-repart(8)` for more information.
       '';
     };