systemd-udev-settle.service is overused #73095
Description
Describe the bug
Related: #53446
Using systemd-udev-settle "is not recommended" (man 8 systemd-udev-settle.service). Nevertheless, we have quite a few services depend on it:
$ rg -l systemd-udev-settle
nixos/tests/misc.nix
nixos/modules/hardware/ksm.nix
nixos/modules/security/lock-kernel-modules.nix
nixos/modules/virtualisation/openvswitch.nix
nixos/modules/virtualisation/libvirtd.nix
nixos/modules/virtualisation/lxd.nix
nixos/modules/virtualisation/anbox.nix
nixos/modules/tasks/kbd.nix
nixos/modules/services/x11/xserver.nix
nixos/modules/services/hardware/tcsd.nix
nixos/modules/services/hardware/brltty.nix
nixos/modules/services/networking/dhcpcd.nix
nixos/modules/services/scheduling/atd.nix
nixos/modules/services/hardware/trezord.nix
nixos/modules/services/hardware/acpid.nix
nixos/modules/system/boot/networkd.nix
nixos/modules/system/boot/systemd.nix
nixos/modules/tasks/filesystems/zfs.nix
On some systems/kernels (e.g. mobile-nixos kernels, cc @samueldr @kirelagin), this can cause boot to wait for systemd-udev-settle to time out, which is no fun.
Expected behavior
Services depend only on the devices that they need, either by waiting for them themselves or by depending on systemd's relevant .device unit.
Metadata
- system:
"aarch64-linux" - host os:
Linux 3.18.71, NixOS, 19.09.941.27a5ddcf747 (Loris) - multi-user?:
yes - sandbox:
yes - version:
nix-env (Nix) 2.3 - channels(root):
"nixos-19.09.941.27a5ddcf747" - nixpkgs:
/nix/var/nix/profiles/per-user/root/channels/nixos