Systemd/User Services

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Systemd supports running a separate instance of systemd for a given user, allowing the user to control their own services. See here for more information: https://wiki.archlinux.org/title/Systemd/User

In NixOS, a user service can be expressed with systemd.user.services.<name>, as documented here: https://search.nixos.org/options?query=systemd.user.services

This may be useful if you want a user to be able to start, stop, and restart their own instance of a service without needing to make the user a sudoer.

Here is an example:

systemd.user.services.my-cool-user-service = {
  enable = true;
  after = [ "network.target" ];
  wantedBy = [ "default.target" ];
  description = "My Cool User Service";
  serviceConfig = {
      Type = "simple";
      ExecStart = ''/my/cool/user/service'';
  };
};

By default, user services will be stopped when the user logs out and will start again when the user logs back in due to us setting wantedBy = [ "default.target" ] in the example.

Enabling the user management service and user process lingering

Without the user management unit user@.service, commands such as systemctl --user will fail, and configured options under systemd.user will not take effect. This is typically observed on minimal systems without a desktop environment.

When lingering is enabled for a user, the user management service is spawned at boot and can run services independently of the user's session, including keeping services running after a user logs out.

You can enable "lingering" by setting users.users.<username>.linger = true; or running sudo loginctl enable-linger [USER...].

For a user service to start at boot, change the service configuration to wantedBy = [ "multi-user.target" ];.

Enabling a service for specific users

By default, enabling a user service enables it for every user for which systemd spawns a service manager. If you wish for the service to be run only for specific users (say, UserA and UserB), use ConditionUser (man 5 systemd.unit):

systemd.user.services.my-cool-user-service = {
  unitConfig.ConditionUser = "UserA|UserB";
};

Likewise, you can also disable a service for a specific user:

systemd.user.services.my-cool-user-service = {
  unitConfig.ConditionUser = "!root";
};

Usage

To interact with user-specific systemd services, use the --user flag with the systemctl command. For example, to check the status of a user service:

 $ systemctl --user status my-cool-user-service

To view logs for a specific user service, use journalctl with the --user-unit option:

 $ journalctl --user-unit my-cool-user-service

To list all active user units:

 $ systemctl --user list-units