XServerPixelBuffer::InitShm() calls Release() when shmget() fails (see https://codesearch.chromium.org/chromium/src/third_party/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc?rcl=8078c53c2f8ed487b1c6bbdf3d541f7a5884ed70&l=155 ). As result the screen and window capturers fails to capture anything, even though it's still possible without using shared memory.