pkgs.systemd does not respect config.systemd.package and
config.boot.initrd.systemd.package overrides. Fix references to the
systemd package to ensure that the udevadm used is copied into the
initrd.
While we're at it, fix the non-initrd reference to systemd as well.
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
because ifstate is not a daemon it can not cope with devices becoming available late
d8e38d4aaa/units/systemd-udev-settle.service (L10-L12)
> This service can dynamically be pulled-in by legacy services which
> cannot reliably cope with dynamic device configurations, and wrongfully
> expect a populated /dev during bootup.
The directory seems to be created by other processes using recent
changes in master now. Therefore the manual mkdir is not needed anymore.
As per the removed code comment, this will probably also be fixed later
in pyroute2 directly.
