Public bug reported:
System: Kubuntu 26.04 LTS
KDE Plasma: 6.6.4
KRDP version: 6.6.4-0ubuntu1
NVIDIA Driver: 595.71.05
Kernel: 7.0.0-22-generic
GPU 1: Intel iHD (card1/renderD128)
GPU 2: NVIDIA T1000 (card2/renderD129)
PROBLEM:
Connecting via Windows 11 mstsc RDP client to KRDP results in
a permanent black screen. Authentication succeeds, portal session
starts, PipeWire pipeline connects, x264 initializes, but no
frames are ever rendered.
ROOT CAUSES IDENTIFIED THROUGH DIAGNOSIS:
1. MISSING DESKTOP FILE: krdpserver registers app ID as
'org.kde.krdp-server' but the installed desktop file is named
'org.kde.krdpserver.desktop' (missing hyphen). This causes:
"Could not register app ID: App info not found for
'org.kde.krdp-server'"
Workaround:
sudo ln -s /usr/share/applications/org.kde.krdpserver.desktop \
/usr/share/applications/org.kde.krdp-server.desktop
2. NVIDIA VA-API CRASH (SIGSEGV): Without nvidia-vaapi-driver
installed, krdpserver crashes with Signal 11 in libavutil.so.60
when VA-API fails and falls back to x264 in a dual-GPU
environment.
Workaround: sudo apt install nvidia-vaapi-driver
3. MB RATE EXCEEDED: At 4K resolution (3840x2160@30fps),
x264 MB rate (32,400,000) exceeds level limit (16,711,680).
krdpserver initializes x264 but silently encodes no frames.
KRDP needs to either cap the stream resolution or negotiate
a higher H.264 level with the client.
4. GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT: The core blocking bug.
When KWin uses NVIDIA (card2) for compositing, the screencast
pipeline produces empty buffers:
kwin_scene_opengl: GL_INVALID_OPERATION - image and target
are incompatible
kwin_scene_opengl: Invalid framebuffer status:
GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT
kwin_screencast: "DP-5" Received stream buffer that does
not contain user data
This is caused by NVIDIA's EGL/GBM implementation not
supporting the texture format KWin uses for screencast
framebuffer attachment. The PipeWire link shows state=active
with BGRA 1920x1080 format negotiated, but all buffers contain
no pixel data. krdpserver CPU usage remains at ~1% confirming
no frames are being encoded.
/etc/environment on this system contains:
GBM_BACKEND=nvidia-drm
__GLX_VENDOR_LIBRARY_NAME=nvidia
KWIN_DRM_DEVICES=/dev/dri/card2
These settings are required for the desktop to function but
cause the screencast framebuffer failure.
ADDITIONAL NOTES:
- KWIN_DRM_FORCE_SOFTWARE_CAPTURE=1 is set but does not resolve
the issue
- KWIN_SCREENCAST_ALLOW_DMABUF=0 does not resolve the issue
- Switching display to 1080p does not resolve the issue
- The bug appears specific to NVIDIA+Intel dual GPU systems where
NVIDIA is used for KWin compositing
- krfb (KDE VNC server) works as a workaround but with poor
performance
** Affects: krdp (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2156242
Title:
KRDP black screen on NVIDIA+Intel dual GPU system -
GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT in KWin screencast
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