A simple script using rsync tool could solve your problem. The script is:

#!/bin/sh

while true

do rsync [source-folder] [destination-machine:folder]

sleep 5 

done

If you want a real-time backup then you can just remove sleep 5 or make it as acomment #sleep 5

To make it autostarted with your user, You can make a launcher then add this launcher to the startup Applications in order to autostart.

Moreover, you can find many other backup tools and other syncronization tools that help you but i just found this script easy to use