[Bug 2130871] [NEW] software-properties-qt fails to start with pkexec on Wayland: “Could not load the Qt platform plugin 'xcb'”

[Rodrigo Lledó]

Public bug reported:

When running pkexec software-properties-qt on Kubuntu 25.10 (Plasma 6.1,
Wayland session), the application crashes immediately with a Qt platform
plugin error related to “xcb”.

This issue only occurs under Wayland; the same command works correctly
under X11 or when run with sudo.

Steps to Reproduce

1. Log into Kubuntu 25.10 using Plasma (Wayland).

2. Open a terminal and run:
pkexec software-properties-qt

3. Observe the crash.

Expected Result

The Software & Updates dialog should open normally with administrative
privileges.

Actual Result

The application aborts with the following error message:

qt.qpa.xcb: could not connect to display 
qt.qpa.plugin: From 6.5.0, xcb-cursor0 or libxcb-cursor0 is needed to load the Qt xcb platform plugin.
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: minimalegl, wayland, vkkhrdisplay,
eglfs, offscreen, wayland-egl, vnc, minimal, linuxfb, xcb.

Aborted (core dumped)

Additional Information

* Package version: software-properties-qt from Kubuntu 25.10
repositories

* libxcb-cursor0 is installed and up to date.

* Running sudo software-properties-qt works fine.

* The GTK version (software-properties-gtk) runs without issues.

* This appears to be a Polkit or Qt platform integration bug under
Wayland.

Workaround

Logging into Plasma (X11) allows the application to run normally.

ProblemType: Bug
DistroRelease: Ubuntu 25.10
Package: software-properties-qt 0.114
ProcVersionSignature: Ubuntu 6.17.0-6.6-generic 6.17.1
Uname: Linux 6.17.0-6-generic x86_64
ApportVersion: 2.33.1-0ubuntu3
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Fri Nov  7 12:30:16 2025
InstallationDate: Installed on 2025-01-12 (299 days ago)
InstallationMedia: Kubuntu 24.04.1 LTS "Noble Numbat" - Release amd64 (20240827)
PackageArchitecture: all
SourcePackage: software-properties
UpgradeStatus: Upgraded to questing on 2025-11-07 (0 days ago)

** Affects: software-properties (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug questing wayland-session

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https://bugs.launchpad.net/bugs/2130871

Title:
  software-properties-qt fails to start with pkexec on Wayland: “Could
  not load the Qt platform plugin 'xcb'”

Status in software-properties package in Ubuntu:
  New

Bug description:
  When running pkexec software-properties-qt on Kubuntu 25.10 (Plasma
  6.1, Wayland session), the application crashes immediately with a Qt
  platform plugin error related to “xcb”.

  This issue only occurs under Wayland; the same command works correctly
  under X11 or when run with sudo.

  Steps to Reproduce

  1. Log into Kubuntu 25.10 using Plasma (Wayland).

  2. Open a terminal and run:
  pkexec software-properties-qt

  3. Observe the crash.

  Expected Result

  The Software & Updates dialog should open normally with administrative
  privileges.

  Actual Result

  The application aborts with the following error message:

  qt.qpa.xcb: could not connect to display 
  qt.qpa.plugin: From 6.5.0, xcb-cursor0 or libxcb-cursor0 is needed to load the Qt xcb platform plugin.
  qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
  This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

  Available platform plugins are: minimalegl, wayland, vkkhrdisplay,
  eglfs, offscreen, wayland-egl, vnc, minimal, linuxfb, xcb.

  Aborted (core dumped)

  Additional Information

  * Package version: software-properties-qt from Kubuntu 25.10
  repositories

  * libxcb-cursor0 is installed and up to date.

  * Running sudo software-properties-qt works fine.

  * The GTK version (software-properties-gtk) runs without issues.

  * This appears to be a Polkit or Qt platform integration bug under
  Wayland.

  Workaround

  Logging into Plasma (X11) allows the application to run normally.

  ProblemType: Bug
  DistroRelease: Ubuntu 25.10
  Package: software-properties-qt 0.114
  ProcVersionSignature: Ubuntu 6.17.0-6.6-generic 6.17.1
  Uname: Linux 6.17.0-6-generic x86_64
  ApportVersion: 2.33.1-0ubuntu3
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CurrentDesktop: KDE
  Date: Fri Nov  7 12:30:16 2025
  InstallationDate: Installed on 2025-01-12 (299 days ago)
  InstallationMedia: Kubuntu 24.04.1 LTS "Noble Numbat" - Release amd64 (20240827)
  PackageArchitecture: all
  SourcePackage: software-properties
  UpgradeStatus: Upgraded to questing on 2025-11-07 (0 days ago)

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