[GH-ISSUE #2772] [APP BUG]: AppImage fails to launch when v4l2loopback Is loaded without input stream #900

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opened 2026-02-27 21:08:46 +03:00 by kerem · 2 comments

kerem commented

2026-02-27 21:08:46 +03:00

Owner

Originally created by @KamiNuke on GitHub (Apr 12, 2025).
Original GitHub issue: https://github.com/shadps4-emu/shadPS4/issues/2772

Checklist

I have searched for a similar issue in this repository and did not find one.
I am using an official build obtained from releases or updated one of those builds using its in-app updater.

Describe the Bug

The application fails to start when the v4l2loopback kernel module is loaded and no video stream is being fed to the dummy device.

This problem does not occur when compiling the app from source, the app works as expected.

When tracing the appimage with strace, it becomes apparent that the application is repeatedly opening /dev/video0 (v4l2loopback)
openat(AT_FDCWD, "/dev/video0", O_RDONLY) = 20
ioctl(20, VIDIOC_QUERYCAP, {driver="v4l2 loopback", card="Dummy video device (0x0000)", bus_info="platform:v4l2loopback-000", version=KERNEL_VERSION(6, 14, 2), capabilities=V4L2_CAP_VIDEO_CAPTURE|V4L2_CAP_VIDEO_OUTPUT|V4L2_CAP_EXT_PIX_FORMAT|V4L2_CAP_READWRITE|V4L2_CAP_STREAMING|V4L2_CAP_DEVICE_CAPS, device_caps=V4L2_CAP_VIDEO_CAPTURE|V4L2_CAP_VIDEO_OUTPUT|V4L2_CAP_EXT_PIX_FORMAT|V4L2_CAP_READWRITE|V4L2_CAP_STREAMING}) = 0
ioctl(20, VIDIOC_ENUM_FMT, {index=0, type=V4L2_BUF_TYPE_VIDEO_CAPTURE, flags=0, description="32-bit BGRA/X 8-8-8-8", pixelformat=v4l2_fourcc('B', 'G', 'R', '4') /* V4L2_PIX_FMT_BGR32 */}) = 0
ioctl(20, VIDIOC_ENUM_FRAMESIZES, {index=0, pixel_format=v4l2_fourcc('B', 'G', 'R', '4') /* V4L2_PIX_FMT_BGR32 */, type=V4L2_FRMSIZE_TYPE_CONTINUOUS}) = 0

Reproduction Steps

Load the v4l2loopback module
sudo modprobe v4l2loopback
Ensure there's no video stream into the virtual device
Launch the appimage
App fails to start(simply stuck and nothing happens)

Expected Behavior

The application should either skip the dummy device or fail with a error.

Specify OS Version

Arch Linux x86_64, kernel 6.14.2

Originally created by @KamiNuke on GitHub (Apr 12, 2025). Original GitHub issue: https://github.com/shadps4-emu/shadPS4/issues/2772 ### Checklist - [x] I have searched for a similar issue in this repository and did not find one. - [x] I am using an official build obtained from [releases](https://github.com/shadps4-emu/shadPS4/releases) or updated one of those builds using its in-app updater. ### Describe the Bug The application fails to start when the v4l2loopback kernel module is loaded and no video stream is being fed to the dummy device. This problem does not occur when compiling the app from source, the app works as expected. When tracing the appimage with strace, it becomes apparent that the application is repeatedly opening /dev/video0 (v4l2loopback) `openat(AT_FDCWD, "/dev/video0", O_RDONLY) = 20` `ioctl(20, VIDIOC_QUERYCAP, {driver="v4l2 loopback", card="Dummy video device (0x0000)", bus_info="platform:v4l2loopback-000", version=KERNEL_VERSION(6, 14, 2), capabilities=V4L2_CAP_VIDEO_CAPTURE|V4L2_CAP_VIDEO_OUTPUT|V4L2_CAP_EXT_PIX_FORMAT|V4L2_CAP_READWRITE|V4L2_CAP_STREAMING|V4L2_CAP_DEVICE_CAPS, device_caps=V4L2_CAP_VIDEO_CAPTURE|V4L2_CAP_VIDEO_OUTPUT|V4L2_CAP_EXT_PIX_FORMAT|V4L2_CAP_READWRITE|V4L2_CAP_STREAMING}) = 0` `ioctl(20, VIDIOC_ENUM_FMT, {index=0, type=V4L2_BUF_TYPE_VIDEO_CAPTURE, flags=0, description="32-bit BGRA/X 8-8-8-8", pixelformat=v4l2_fourcc('B', 'G', 'R', '4') /* V4L2_PIX_FMT_BGR32 */}) = 0` `ioctl(20, VIDIOC_ENUM_FRAMESIZES, {index=0, pixel_format=v4l2_fourcc('B', 'G', 'R', '4') /* V4L2_PIX_FMT_BGR32 */, type=V4L2_FRMSIZE_TYPE_CONTINUOUS}) = 0` ### Reproduction Steps 1. Load the v4l2loopback module `sudo modprobe v4l2loopback` 2. Ensure there's no video stream into the virtual device 3. Launch the appimage 4. App fails to start(simply stuck and nothing happens) ### Expected Behavior The application should either skip the dummy device or fail with a error. ### Specify OS Version Arch Linux x86_64, kernel 6.14.2