Control user services on non-NixOS

[khlopkov]

Description

I use Home Manager on a non-NixOS (Debian in my case). Home Manager installed few systemd services with a packages into ~/.nix-profile/share/systemd/user/ from nixpkgs. Those services can not be found, for example this command:

systemctl --user restart xdg-desktop-portal-gtk

gives the following output:

Failed to restart xdg-desktop-portal-gtk.service: Unit xdg-desktop-portal-gtk.service not found.

I was able to fix this by adding a symlink from the `~/.nix-profile/share/systemd to the ~/.config/systemd:

ln -s ~/.nix-profile/share/systemd/ ~/.config/systemd

But there are few issues with this workaround:

1. I can not enable those services from my Home Manager configuration and have to enable them manually.
2. It conflicts with the xdg.portal.enable (and I suppose with other services that can be enabled through the Home Manager). It prints following when trying to set this option to true:

   Existing file '/home/etsilence/.config/systemd/user/xdg-desktop-portal.service' is in the way of '/nix/store/d3yw2n212zbz7473pbwwc41dj1ipkk8x-home-manager-files/.config/systemd/user/xdg-desktop-portal.service'

It can be fixed by linking specific services into :

ln -s ~/.nix-profile/share/systemd/user/xdg-desktop-portal-gtk.service ~/.config/systemd/user/xdg-desktop-portal-gtk.service

But in this case I have to symlink each required service

There is a similar issue: https://github.com/nix-community/home-manager/issues/4922, but I started a new one, because this thread is about more wide problem rather just a problem with a xdg.portal.enable option. Will it be possible to control over systemd.user services installed from nixpkgs on non NixOS environments?

[khlopkov]

@baloo from the linked issue's thread suggested adding this activation script into home-manager's configuration:

  home.activation.linkSystemd = let
    inherit (lib) hm;
  in hm.dag.entryBefore [ "reloadSystemd" ] (''
    find $HOME/.config/systemd/user/ \
      -type l \
      -exec bash -c "readlink {} | grep -q $HOME/.nix-profile/share/systemd/user/" \; \
      -delete

    find $HOME/.nix-profile/share/systemd/user/ \
      -type f -o -type l \
      -exec ln -s {} $HOME/.config/systemd/user/ \;
  '');

Is it possible to merge something similar to the home-manager master branch?

The decision above, LGTM, because it should replace only those files controlled by Home Manager. But it will also replace custom services declared by user via home-manager. Also, this script should fail in case when user manually (not by Home Manager) added a .service file into $HOME/.config/systemd/user/ and it is also declared in $HOME/.nix-profile/share/systemd/user/. So I am not sure this specific script can be merged into a master branch.

I probably would like to contribute this change into Home Manager, but I think it needs some discussion before

[khlopkov]

Probably that's out of scope of the issue, but I think there are also some other files that should be linked into user's home: .application files of packages, dbus interfaces and services

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[CyberShadow]

Why does home-manager create some unit file links in ~/.config/systemd/user, and some in ~/.nix-profile/share/systemd/user?

Maybe it would be simpler to make it create everything in ~/.nix-profile/share/systemd/user, then on non-NixOS, ~/.config/systemd/user could be symlinked to it?