Permanently disable systemd services

mz-gh · May 23, 2018, 5:04pm

Hi All!

I’m just started to learn to configure and use NixOS, so maybe I’m still missing some basic concepts and I can’t figure out how to permanently disable systemd services using the configuration file.

I’ve tried this:

systemd.services = {
    ModemManager = {
      enable = false;
      restartIfChanged = false;
    };
  };

After a nixos-rebuild switch it’s fine: the ModemManager.service is shut down. However after a reboot it’s up and running again. Is it possible to preserve the disabled state after a reboot?
I’ve looked around in the manual and also here in discourse but to no avail.

Thanks in advance!
Cheers!

danbst · May 23, 2018, 8:17pm

Interesting. I’d say this deserves an issue on Nixpkgs bugtracker.

You may disable NM using another option:
https://nixos.org/nixos/options.html#networking.networkmanager.enable

networking.networkmanager.enable = lib.mkForce false;

(The lib.mkForce says explicit and loud to override any other settings for this option)

mz-gh · May 23, 2018, 8:30pm

Thanks for your answer!
The service I was asking for is ModemManager, which doesn’t seem to have an option (according to the page, you linked).
A more general question could be: how to make systemctl disable permanent?

danbst · May 23, 2018, 9:20pm

Oh, sorry, it was ModemManager.

Have you tried (lower-case, not CamelCase) unit name

systemd.services.modem-manager.enable = false;

?

mz-gh · May 24, 2018, 7:24pm

I’ve tried it, but in this case, it won’t even stop it on rebuild switch…
Using my original setup, this is the systemctl status output for ModemManager after reboot:

● ModemManager.service - Modem Manager
   Loaded: loaded (/nix/store/cd96xz87sp2lvipn6lm22yc5rihy63b2-ModemManager-1.6.8/etc/systemd/system/ModemManager.service; masked; vendor preset: enabled)
   Active: active (running) since Thu 2018-05-24 18:51:32 CEST; 2h 20min ago
 Main PID: 1175 (ModemManager)
    Tasks: 3 (limit: 4915)
   CGroup: /system.slice/ModemManager.service
           └─1175 /nix/store/cd96xz87sp2lvipn6lm22yc5rihy63b2-ModemManager-1.6.8/sbin/ModemManager

máj 24 18:51:31 nixos systemd[1]: Starting Modem Manager...
máj 24 18:51:32 nixos ModemManager[1175]: <info>  ModemManager (version 1.6.8) starting in system bus...
máj 24 18:51:32 nixos systemd[1]: Started Modem Manager.
máj 24 18:51:34 nixos ModemManager[1175]: <info>  Couldn't check support for device at '/sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0': not supported by any plugin
máj 24 18:51:34 nixos ModemManager[1175]: <info>  Couldn't check support for device at '/sys/devices/pci0000:00/0000:00:1c.3/0000:04:00.0': not supported by any plugin
máj 24 20:57:07 nixos ModemManager[1175]: <info>  Couldn't check support for device at '/sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0': not supported by any plugin
máj 24 20:57:07 nixos ModemManager[1175]: <info>  Couldn't check support for device at '/sys/devices/pci0000:00/0000:00:1c.3/0000:04:00.0': not supported by any plugin

So, it says it is masked. What I do not understand is that, as far as I know, this means that systemd won’t start it even if another service depends on it…

Edit: this is the output after nixos-rebuild switch:
● ModemManager.service
Loaded: masked (/dev/null; bad)
Active: inactive (dead)

máj 25 07:21:32 nixos systemd[1]: Starting Modem Manager...
máj 25 07:21:33 nixos ModemManager[1047]: <info>  ModemManager (version 1.6.8) starting in system bus...
máj 25 07:21:33 nixos systemd[1]: Started Modem Manager.
máj 25 07:21:35 nixos ModemManager[1047]: <info>  Couldn't check support for device at '/sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0': not supported by any plugin
máj 25 07:21:35 nixos ModemManager[1047]: <info>  Couldn't check support for device at '/sys/devices/pci0000:00/0000:00:1c.3/0000:04:00.0': not supported by any plugin
máj 25 07:22:44 nixos ModemManager[1047]: <info>  Caught signal, shutting down...
máj 25 07:22:44 nixos systemd[1]: Stopping Modem Manager...
máj 25 07:22:44 nixos ModemManager[1047]: <info>  ModemManager is shut down
máj 25 07:22:44 nixos systemd[1]: Stopped Modem Manager.

danbst · May 24, 2018, 9:15pm

Yeah, I confirm this too. Reported at Can't disable NixOS service modem-manager · Issue #41055 · NixOS/nixpkgs · GitHub

NixOS disables units by symlinking them to /dev/null on activation. I don’t understand why it isn’t symlinked to /dev/null after reboot…

Maybe you can find more insights here

github.com

NixOS/nixpkgs/blob/master/nixos/modules/system/boot/systemd-lib.nix#L159

    
      
            x=$out/$(basename $fn)
            mkdir $x
            for i in $fn/*; do
              y=$x/$(basename $i)
              cp -pd $i $y
              if ! [ -e $y ]; then rm $y; fi
            done
          done
          
          
# Symlink all units provided listed in systemd.packages.
          packages="${toString cfg.packages}"
          
          
# Filter duplicate directories
          declare -A unique_packages
          for k in $packages ; do unique_packages[$k]=1 ; done
          
          
for i in ''${!unique_packages[@]}; do
            for fn in $i/etc/systemd/${type}/* $i/lib/systemd/${type}/*; do
              if ! [[ "$fn" =~ .wants$ ]]; then
                if [[ -d "$fn" ]]; then
                  targetDir="$out/$(basename "$fn")"

mz-gh · May 25, 2018, 5:30am

Thanks for reporting it, I added some more information to my previous post!

danbst · June 5, 2018, 9:28am

Breaking news, it’s indeed a bug in Nixpkgs/NixOS

github.com/NixOS/nixpkgs

Can't disable NixOS service modem-manager

opened 09:11PM - 24 May 18 UTC

danbst

6.topic: nixos 2.status: stale

## Issue description Given following module change: ``` { networking.netwo…rk-manager.enable = true; } ----> { networking.network-manager.enable = true; systemd.services.modem-manager.enable = false; # <-- this line was added } ``` We get inconsistent behavior on activation: 1. When doing `nixos-rebuild switch`, `modem-manager` service is stopped. 2. But on system start (or reboot), `modem-manager` service is started. On subsequent `nixos-rebuild switch` it is stopped. ### Steps to reproduce When using Network Manager try to disable Modem Manager service. Even it is stopped, it is then started after reboot Reported in https://discourse.nixos.org/t/permanently-disable-systemd-services/263/1 ## Technical details NixOS 18.03

I’ve pointed there to a workaround, but I can’t think now of a proper solution.