nixos: use user service for activation

[pasqui23]

Description

Use user units to activate home configurations. This has several benefits:

1. Less units are run on startup, especially if more than one user is configured
2. Home manager can access $XDG_RUNTIME_DIR, including calling dbus units
3. Commands depending on X or Wayland are similarly aviable

ssh is special cased so that its config file still is linked on boot to allow remote login.
If other components needs to be similarly special cased I could rework this PR to include a few dedicated options.

EDIT(@ncfavier): fixes #3415

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all.

• Test cases updated/added. See example.

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[pasqui23]

I also suspect that this will fix https://gitlab.com/rycee/sd-switch/-/issues/2

[ncfavier]

Hi, I've rebased this PR against master following #2971: ncfavier@d28c365. Feel free to force-pull from my fork:

git fetch https://github.com/ncfavier/home-manager nixos-late-start
git reset --hard FETCH_HEAD

(I haven't reviewed the changes, only fixed the conflicts.)

[pasqui23]

@rycee why the test is failing with

error: The option `systemd.user' does not exist. Definition values:
       - In `/home/runner/work/home-manager/home-manager/nixos/default.nix':
           {
             _type = "if";
             condition = false;
             content = {
               services = {
           ...
(use '--show-trace' to show detailed location information)
Uh oh, the installation failed! Please create an issue at
   [ https://github.com/nix-community/home-manager/is](https://github.com/nix-community/home-manager/issues)
if the error seems to be the fault of Home Manager.

?

[stale]

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[pasqui23]

This compiles and works without any problems.
@rycee I am ready for review.

[ncfavier]

I think this should be hidden behind an option home-manager.useUserService or somesuch and default to false at first. That way we could merge sooner without worrying about breaking people's configurations.

[gkleen]

@rycee bump?

[stale]

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[mikunimaru]

This is the best patch. With the introduction of this feature, errors no longer occur on systems that mount the home folder at login.

[stale]

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[gkleen]

@rycee bump?

[rycee]

Yeah, sorry about the long delay here. I'm very much in favor of doing this, and ultimately I would like for activation through systemd to be the normal procedure, even for standalone installations.

I've been slowly working towards this, for example, by experimenting in #4976.

That said, perhaps it's worth getting this in before that work is done.

[nyabinary]

Yeah, sorry about the long delay here. I'm very much in favor of doing this, and ultimately I would like for activation through systemd to be the normal procedure, even for standalone installations.

I've been slowly working towards this, for example, by experimenting in #4976.

That said, perhaps it's worth getting this in before that work is done.

Eventually, this can lead to upstreaming home manager (via a optional module) in nixpkgs right?

[mikunimaru]

My environment-specific issues were resolved with this patch.
I have been using this patch for several months and have not had any problems.
This patch has minimal impact on users other than those who have explicitly enabled it, so I would be happy if it was merged as soon as possible.

[gkleen]

My environment-specific issues were resolved with this patch. I have been using this patch for several months and have not had any problems. This patch has minimal impact on users other than those who have explicitly enabled it, so I would be happy if it was merged as soon as possible.

ditto

[mikunimaru]

I have already cherry-picked and used this best patch.
Is it possible to resolve the conflict for use with home manager on master branch?

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[urioTV]

bump

This PR is really important. And it's just an option to make it user service, not forcing it to be one.