Yeah use a little pacakge called "overlayroot" newer image have it
installed by default..
If you dont:
sudo apt update
sudo apt install overlayroot
Then make sure to regenerate the initrd..
sudo update-initramfs -uk `uname -r`
Then in /boot/uEnv.txt append this variable to your existing cmdline settings.
cmdline=(existing settings) overlayroot=tmpfs
Then reboot, your system is now "Read Only"..
So Beyond that, what's really really nice about overlayroot, you can
login and actually write stuff to the drive by doing:
sudo overlayroot-chroot
Regards,
--
Robert Nelson
https://rcn-ee.com/