dynamic wallpaper background

1. sudo apt install mcron
2. Create a script, say /home/chiao/scripts/dynwall:
   #!/bin/bash
   sleep 3
   IMG=`find  /home/chiao/圖片/wallpaper/dawn/*.jpg | shuf -n 1`
   gsettings set org.gnome.desktop.background picture-options 'stretched'
   /usr/bin/gsettings set org.gnome.desktop.background picture-uri file:///${IMG}
3. Create /home/chiao/.config/cron/job.vixie
   5 * * * * /home/chiao/scripts/dynwall
   
4. Create /home/chiao/.config/autostart/mcron.desktop
   [Desktop Entry]
   Type=Application
   Exec=/usr/bin/mcron -d
   Hidden=false
   NoDisplay=false
   X-GNOME-Autostart-enabled=true
   Name[zh_TW]=mcron
   Name=mcron
   Comment[zh_TW]=
   Comment=
5. Reboot