Qt app cannot connect to session bus

Development
1

I trying to get a VPN client running on NixOS. The binaries have all their dependencies resolved and the application runs, but it reports that it cannot connect to the D-Bus session bus:

2020-04-10,15:21:02:223, 10685,10685,, 1, /LinuxService.h, 75, bool f5::qt::setupDBusService(f5::qt::CustomQApplication&), Cannot connect to session bus

Here’s my expression:

{ stdenv
, dpkg
, makeWrapper
, buildFHSUserEnv
, glib
, libGL
, libxml2
, libxslt
, fontconfig
, freetype
, sqlite
, libICE
, libSM
, libXcomposite
, libXi
, libXrender
, xkeyboard_config
}:

let
  f5vpn-dpkg = stdenv.mkDerivation {
    name = "f5vpn-dpkg";
    src = ./linux_f5vpn.x86_64.deb;

    nativeBuildInputs = [
      dpkg
      makeWrapper
      xkeyboard_config
    ];

    dontConfigure = true;
    dontBuild = true;

    sourceRoot = ".";
    unpackCmd = ''dpkg -x $src $out'';

    installPhase = ''
      makeWrapper \
          $out/opt/f5/vpn/f5vpn \
          $out/bin/f5vpn \
          --prefix "QT_XKB_CONFIG_ROOT" ":" "${xkeyboard_config}/share/X11/xkb"
      mkdir -p $out/share/applications
      cp $out/opt/f5/vpn/com.f5.f5vpn.desktop $out/share/applications
      substituteInPlace \
          $out/share/applications/com.f5.f5vpn.desktop \
          --replace "/opt/f5/vpn/f5vpn" "$out/bin/f5vpn"
      mkdir -p $out/share/dbus-1/services
      cp $out/opt/f5/vpn/com.f5.f5vpn.service $out/share/dbus-1/services
      substituteInPlace \
          $out/share/dbus-1/services/com.f5.f5vpn.service \
          --replace "/opt/f5/vpn/f5vpn" "$out/bin/f5vpn"
    '';

    preFixup = ''
      patchelf --remove-rpath $out/opt/f5/vpn/f5vpn
      patchelf --set-rpath $out/opt/f5/vpn/lib $out/opt/f5/vpn/f5vpn
    '';
  };
in
  buildFHSUserEnv {
    name = "f5vpn-fhs";
    targetPkgs = pkgs: [
      f5vpn-dpkg
      pkgs.glib
      pkgs.libGL
      pkgs.libxml2
      pkgs.libxslt
      pkgs.fontconfig
      pkgs.freetype
      pkgs.sqlite
      pkgs.xorg.libICE
      pkgs.xorg.libSM
      pkgs.xorg.libX11
      pkgs.xorg.libxcb
      pkgs.xorg.libXcomposite
      pkgs.xorg.libXext
      pkgs.xorg.libXi
      pkgs.xorg.libXrender
      pkgs.zlib
    ];
    runScript = "f5vpn";
  }

I went for buildFHSUserEnv because I can see that it relies on some absolute paths when I run it on Ubuntu, but the same thing happens if I build it with autoPatchelfHook.

It’s worth mentioning that with steam-run, the application actually gets past the session bus point, but there are other issues (eventually a segfault), and I really don’t want to go down that road without understanding why it won’t work in my own FHS sandbox.

I also tried using the Qt-specific mkDerivation (as outlined in Nixpkgs 23.11 manual | Nix & NixOS), but I cannot see how that would matter since I already resolved the dependencies. It didn’t make a difference anyway.

Any ideas? Are there any differences in how NixOS handles D-Bus compared to other distros?

2

How are you running it?

3

The application is meant to be invoked by Firefox via D-Bus, but since it cannot make that connection I use dbus-monitor to see what arguments the browser tries to call it with, and run that on the command line. That works on my reference OS.

So I build, install and run f5vpn-fhs [args].

4

I’m guessing that the fhs env doesn’t inherit your DBUS_SESSION_BUS_ADDRESS variable. What happens if you do echo $DBUS_SESSION_BUS_ADDRESS inside the environment?

5

DBUS_SESSION_BUS_ADDRESS is unix:abstract=/tmp/dbus-kUlK1qRnsn,guid=7ceee477209ad70e4a23d6e05eb0101d - the same address as outside of the FHS. Which looks valid, right? Tried unsetting it see if the program would complain about it, but the same log statement stands.

6

Mine looks like this:

unix:path=/run/user/1000/bus

I’m guessing that you have something spawning dbus instead of having it socket activated and /tmp is then a separate filesystem inside the env.

Set services.dbus.socketActivated = true; (this really should be the default), nixos-rebuild, log out and back in, check $DBUS_SESSION_BUS_ADDRESS and if it looks like mine, it should work.

7

That makes sense - I’ll keep that setting regardless - but alas, it did not make a difference. I checked the address and it looks just like yours inside the FHS environment.

Hard to tell how it tries to connect since I don’t have access to the source, but I assume it’s using the Qt D-Bus API. As I said above, I do have a reference working install on Ubuntu - perhaps there is somewhere I can look for hints on how it (successfully) connects there?

(btw thanks for answering these!)

8

Try to execute this inside the env:

dbus-send \
   --session \
   --type=method_call \
   --print-reply \
   --dest=org.freedesktop.DBus \
   /org/freedesktop/DBus org.freedesktop.DBus.ListNames

This will tell you if you can connect to dbus. Then try again with --session replaced by --system and see if you can connect to the system dbus.

9

Looks like I can connect to both buses from inside the environment:

$ dbus-send --session --type=method_call --print-reply --dest=org.freedesktop.DBus /org/freedesktop/DBus org.freedesktop.DBus.ListNames
method return time=1588753394.340692 sender=org.freedesktop.DBus -> destination=:1.25 serial=3 reply_serial=2
   array [
      string "org.freedesktop.DBus"
      string "org.freedesktop.PowerManagement"
      (...)
      string ":1.5"
      string ":1.6"
   ]

$ dbus-send --system --type=method_call --print-reply --dest=org.freedesktop.DBus /org/freedesktop/DBus org.freedesktop.DBus.ListNames
method return time=1588753405.450942 sender=org.freedesktop.DBus -> destination=:1.72 serial=3 reply_serial=2
   array [
      string "org.freedesktop.DBus"
      string "org.freedesktop.login1"
      (...)
      string "fi.w1.wpa_supplicant1"
      string "org.freedesktop.Accounts"
   ]
10

I’m out of ideas. Maybe open a ticket with the vendor?

11

In case anyone else needs to install the F5 VPN client with Nix and finds this: I never managed to get it working, but I found this and packaged it for Nix: GitHub - evenbrenden/svpn-login: Connect to a F5 BIG-IP APM VPN server using the FastPPP protocol without any graphical frontend