linux ffmpeg get rtmp stream and convert into a live webcam v4l2 - ffmpeg

Question

So I simply try out to get the stream and convert it into a rawvideo and create a new webcam with v4l2.
ffmpeg -i "rtmp://XX.XX.XXX.XXX/XXXXXXXXXXXX/test" -vcodec rawvideo -y -f v4l2 /dev/video2
It is working a long time and then I got this:
ffmpeg version 2.7.1 Copyright (c) 2000-2015 the FFmpeg developers
built with gcc 5.1.0 (GCC)
configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-avisynth --enable-avresample --enable-fontconfig --enable-gnutls --enable-gpl --enable-libass --enable-libbluray --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libschroedinger --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-shared --enable-version3 --enable-x11grab
libavutil 54. 27.100 / 54. 27.100
libavcodec 56. 41.100 / 56. 41.100
libavformat 56. 36.100 / 56. 36.100
libavdevice 56. 4.100 / 56. 4.100
libavfilter 5. 16.101 / 5. 16.101
libavresample 2. 1. 0 / 2. 1. 0
libswscale 3. 1.101 / 3. 1.101
libswresample 1. 2.100 / 1. 2.100
libpostproc 53. 3.100 / 53. 3.100
Input #0, flv, from 'rtmp://XX.XX.XXX.XXX/XXXXXXXXXXXX/test':
Metadata:
fileSize : 0
audiochannels : 2
encoder : obs-output module (libobs version 0.10.1-67-g94edb7f)
Duration: 00:00:00.00, start: 1774.608000, bitrate: N/A
Stream #0:0: Video: h264 (High), yuv420p(tv, bt709), 1920x1080, 2560 kb/s, 30.30 fps, 30 tbr, 1k tbn, 60 tbc
Stream #0:1: Audio: aac (LC), 44100 Hz, stereo, fltp, 196 kb/s
[v4l2 # 0x7f7326cb4480] Unable to open V4L2 device '/dev/video2'
Output #0, v4l2, to '/dev/video2':
Metadata:
fileSize : 0
audiochannels : 2
encoder : Lavf56.36.100
Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 1920x1080, q=2-31, 200 kb/s, 30 fps, 30 tbn, 30 tbc
Metadata:
encoder : Lavc56.41.100 rawvideo
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> rawvideo (native))
Could not write header for output file #0 (incorrect codec parameters ?): No such file or directory

Answer 1

To create virtual video devices you need to install and enable v4l2loopback. The "No such file or directory" message means you didn't enable the device.
sudo modprobe v4l2loopback video_nr=2
This will create the /dev/video2 device.
Update: in response to umläute's comment make sure the v4l2loopback module is persistent, just in case your server reboots. Uptime can be very long.
Example for CentOS: Persistent Module Loading