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1e4eb2df3f
This service is essentially a random sleep() call that old software that is unable to properly handle modern hardware initialisation being asynchronous can use to *mostly* get by. Over the years is has caused so many issues in NixOS, like introducing long delays in the boot process[1], complete deadlocks[2] and even failures when reloading services or activating a new configuration[3]. systemd has been discouraging its use since 2011 (15 years ago!), then it officially deprecated it in 2018 and since 2020 it started to show on every boot a huge wall of text calling out all the offending services that still use it. Around 2021 we managed to fix around 15 NixOS modules[4] that were relying on systemd-udev-settle and practically ZFS[5] was the only remaining one. However, since then, people have actually started to bring it back with new services[6][7][8]. This is not acceptable. So, to prevent any more (lazy) uses of systemd-udev-settle, we stop providing the systemd-udev-settle.service unit entirely. For existing modules that unfortunately still need it, we replace it with the command `udevadm settle --timeout=180`, which is all that the service does. Hopefully this will also increase the awareness that it's bad and something to be fixed. Note: I tested this change using - `nixosTests.zfs`, - `nixosTests.ifstate`, - `nixosTests.misc`, - `nixosTests.openvswitch`, - `nixosTests.predictable-interface-names` - `nixosTests.nvidia-container-toolkit` and making sure that none of the 165 packages that provide upstream units (via the `systemd.packages` option) had a dependency on systemd-udev-settle.service. [1]: https://github.com/NixOS/nixpkgs/pull/25311 [2]: https://github.com/NixOS/nixpkgs/issues/107341 [3]: https://github.com/NixOS/nixpkgs/pull/113804 [4]: https://github.com/NixOS/nixpkgs/issues/73095 [5]: https://github.com/openzfs/zfs/issues/10891 [6]: https://github.com/NixOS/nixpkgs/pull/257525#discussion_r1442702970 [7]: https://github.com/NixOS/nixpkgs/pull/460075 [8]: https://github.com/NixOS/nixpkgs/pull/284507