Adding NixOS option for systemd user lingering

Development
1

I have started using the systemd “user lingering” feature on one of my NixOS systems, and I would like to add a NixOS option for controlling this functionality. From the loginctl(1) man page:

enable-linger [USER...], disable-linger [USER...]
Enable/disable user lingering for one or more users. If enabled for a specific user, a user manager is spawned for the user at boot and kept around after logouts. This allows users who are not logged in to run long-running services. Takes one or more user names or numeric UIDs as argument. If no argument is specified, enables/disables lingering for the user of the session of the caller.

Enabling this this simply creates an empty file at /var/lib/systemd/linger/USER.

I think the option belongs either in users.users.<name> as a boolean attribute, or in systemd.users as a list of usernames. As far as I can tell, there are no systemd-related options under users.users.<name>, so systemd.users seems the more appropriate place. I would like to get some feedback before opening a pull request to implement the option.

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2

Out of curiosity, what is the use-case here?

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The system is a headless server, and this allows users to have Syncthing (installed via home-manager) running when not logged in.

4

If it’s a headless server without any interactive users, can’t you run syncthing using the nixos module instead?

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There are interactive users, and Syncthing is designed to be run as a normal user if you want multi-user support.

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If you don’t have enough feedback, consider pinging the people listed as maintainers of the package you intend to contribute to. The maintainers are in the package files somewhere.

1 Like
7

It’s not super elegant, but you can simply do

# Enable linger for some user
systemd.tmpfiles.rules = [
  "f /var/lib/systemd/linger/alice"
  "f /var/lib/systemd/linger/bob"
];
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related Enabling persistent user instance systemd · Issue #3702 · NixOS/nixpkgs · GitHub

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9

Linger is important for running Docker services in rootless mode. Otherwise you need a logged-in user session for the containers to stay up, which is not ideal for network services that are supposed to be persistent.

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I run zigbee2mqtt in a container, but no lingering is needed for that. podman runs in a regular systemd system unit with DynamicUser = yes set.

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Possibly, I haven’t figured out the incantations needed to get docker compose into a NixOS systemd unit. But linger worked for my purposes.

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I haven’t had a need for docker/podman-compose, so I can’t really say anything about that, but you can configure containers through virtualisation.oci-containers which is what I do for zigbee2mqtt. Very straight-forward.