If you define a unit, and either systemd or a package in
systemd.packages already provides that unit, then we now generate a
file /etc/systemd/system/<unit>.d/overrides.conf. This makes it
possible to use upstream units, while allowing them to be customised
from the NixOS configuration. For instance, the module nix-daemon.nix
now uses the units provided by the Nix package. And all unit
definitions that duplicated upstream systemd units are finally gone.
This makes the baseUnit option unnecessary, so I've removed it.
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
This allows to define systemd.path(5) units, for example like this:
{
systemd = let
description = "Set Key Permissions for xyz.key";
in {
paths.set-key-perms = {
inherit description;
before = [ "network.target" ];
wantedBy = [ "multi-user.target" ];
pathConfig.PathChanged = "/run/keys/xyz.key";
};
services.set-key-perms = {
inherit description;
serviceConfig.Type = "oneshot";
script = "chown myspecialkeyuser /run/keys/xyz.key";
};
};
}
The example here is actually useful in order to set permissions for the
NixOps keys target to ensure those permisisons aren't reset whenever the
key file is reuploaded.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
You can now say:
systemd.services.foo.baseUnit = "${pkgs.foo}/.../foo.service";
This will cause NixOS' generated foo.service file to include
foo.service from the foo package. You can then apply local
customization in the usual way:
systemd.services.foo.serviceConfig.MemoryLimit = "512M";
Note however that overriding options in the original unit may not
work. For instance, you cannot override ExecStart.
It's also possible to customize instances of template units:
systemd.services."getty@tty4" =
{ baseUnit = "/etc/systemd/system/getty@.service";
serviceConfig.MemoryLimit = "512M";
};
This replaces the unit options linkTarget (which didn't allow
customisation) and extraConfig (which did allow customisation, but in
a non-standard way).
