Has anyone tried the overlayFS option now available via raspi-config, under performance section? It creates a read-only file system. Testing it here it seems to work.
A discussion on the raspberrypi forums:
based on this original script I believe:
and useful information here:
Note: When the overlay filesystem is in place your RPI will function as usual, but any data generated after startup is only saved in RAM and will be lost upon reboot.
It seems like a particularly useful way of creating basic gateway images with emonhub posting data to a remote server.
You need to enable it via raspi-config rather than the overlayfs commands described in the ghollingworth repo: