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).
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