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2configs/autoupdate: skip auto-upgrade when the flake is older than the running system
author
lassulus
date
(Aug 6, 2026, 8:52 AM CEST)
commit
16fbb947
16fbb947662def7b5e80f24a0ffe52c06e61bf83
parent
acf512ff
acf512ff1b29e8c724e9cae2cd241d5b3f46cfef
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-1
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2configs/autoupdate.nix
+48
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2configs/autoupdate.nix
···
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{
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config,
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lib,
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pkgs,
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self,
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...
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}:
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let
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flake = "github:lassulus/superconfig";
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# Timestamp of the flake revision this system was built from, baked into the
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# closure so the running system knows how old its own source is.
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stampFile = "/run/current-system/source-lastModified";
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# system.autoUpgrade switches to whatever the flake currently evaluates to,
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# forwards or backwards. A machine deployed from an unpushed local checkout
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# therefore gets reverted to the older remote HEAD on the next timer run.
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# Refuse to move backwards in time.
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guard = pkgs.writeShellApplication {
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name = "autoupgrade-forward-only";
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runtimeInputs = [
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config.nix.package
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pkgs.coreutils
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pkgs.jq
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];
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text = ''
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stamp=''${1:-${stampFile}}
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current=$(cat "$stamp" 2>/dev/null || echo 0)
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if ! meta=$(nix flake metadata --refresh --json ${lib.escapeShellArg flake}); then
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echo "autoupgrade: cannot reach ${flake}; letting nixos-upgrade report the error"
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exit 0
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fi
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remote=$(jq -r '.lastModified // 0' <<<"$meta")
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if [ "$remote" -gt "$current" ]; then
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exit 0
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fi
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echo "autoupgrade: ${flake} is at $remote, running system is at $current; skipping"
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exit 1
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'';
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};
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in
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{
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system.autoUpgrade = {
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enable = true;
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flake = "github:lassulus/superconfig";
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inherit flake;
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randomizedDelaySec = "6h";
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};
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system.extraSystemBuilderCmds = ''
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echo -n ${toString (self.lastModified or 0)} > $out/source-lastModified
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'';
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systemd.services.nixos-upgrade.serviceConfig.ExecCondition = lib.getExe guard;
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}