Install ffmpeg.
$ sudo apt-get install ffmpeg
Run command on terminal or create a rec.sh
ledate=$(date +"%Y%m%d-%H%M%S")
ffmpeg -f x11grab -s 1366x768 -r 25 -i :0.0 -acodec pcm_s16le -f alsa -ac 2 -i pulse ~/desktop_$ledate.mkv
If run rec.sh
...
$ ./rec.sh