Q: How to set up (L)ubuntu to use read only-fs on raspberry? I want to set up an Lubuntu-Kiosk read-only. So I want everything that user does, written in the RAM only. When the Raspberry is restarted, everything is deleted. 
I have tried using the package overlayroot: 
apt install overlayroot
nano /etc/overlayroot.conf

#--> overlayroot = "tmpfs"**
#REBOOT

But it didn't work. 
I have got Lubuntu from: Ubuntu Pi flavour maker 
Update: Content of /etc/overlayroot.conf
# This is the overlayroot config file
# ... nothing changed ...
#    which is a tmpfs in memory.
overlayroot_cfgdisk="disabled"
overlayroot="tmpfs"

Update 2
I also tried to regenerate initramfs (after change as proposed in Felix' link to Odroid forum: sudo update-initramfs -c -k $(uname -r)), nothing changed.
Also, lsmod does not show overlayfs module to be loaded.
