Automatically change Ubuntu wallpaper at a certain hour

1. I'm not sure, but maybe you have to install dconf first

   sudo apt-get install dconf-cli
   

2. Edit your crontab

   crontab -e
   

3. Add an entry for each background image

   */5 4,5,6,7 * * *   /path/to/change_wallpaper '/path/of/your/wallpaper/for/4am'
   */5 8,8,9,10,11 * * *   /path/to/change_wallpaper '/path/of/your/wallpaper/for/8am'
   */5 12,13,14 * * *   /path/to/change_wallpaper '/path/of/your/wallpaper/for/12am'
   */5 15,16,17 * * *   /path/to/change_wallpaper '/path/of/your/wallpaper/for/3pm'
   */5 18,19 * * *   /path/to/change_wallpaper '/path/of/your/wallpaper/for/6pm'
   */5 20,21,22,23,0,1,2,3 * * *   /path/to/change_wallpaper '/path/of/your/wallpaper/for/8pm'
   

   • The interval is set to 5 minutes (*/5).
   • The lowest possible interval is 1 minute (*/1 or *)

4. Save and close your crontab editor

5. Create the script

   nano change_wallpaper
   

6. Add the code below

   #!/bin/bash -e
   user=$(whoami)
   
   fl=$(find /proc -maxdepth 2 -user "$user" -name environ -print -quit)
   for i in {1..5}
   do
     fl=$(find /proc -maxdepth 2 -user "$user" -name environ -newer "$fl" -print -quit)
   done
   
   export DBUS_SESSION_BUS_ADDRESS
   DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS "$fl" | cut -d= -f2-)
   
   IMG="file://$1"
   if [ "$(gsettings get org.gnome.desktop.background picture-uri)" != "$FILE" ]; then
       dconf write "/org/gnome/desktop/background/picture-uri" "'file://${IMG}'"
      # gsettings set org.gnome.desktop.background picture-uri "'$IMG'"
   fi
   

   • The script works with dconf or gsettings. You can switch between both methods. Simply move the # in the front of the gsettings … line to the dconf … line

7. Make it executable

   chmod +x change_wallpaper
   

8. Test the script in your crontab

   • Edit your crontab again

     crontab -e
     

   • Add the (temporary) line below

     */1 * * * *   /path/to/change_wallpaper '/path/of/any/wallpaper'
     

   • Close the crontab editor

   • Wait a minute

9. If the script works, remove the test entry

   • Edit your crontab again

     crontab -e
     

   • Remove the (temporary) line below

     */1 * * * *   /path/to/change_wallpaper '/path/of/any/wallpaper'
     

   • Close the crontab editor

_{Script partially taken from here}