Acknowledgment

overlayRoot is based on a script published by Pascal Sutter on the Raspberry Forums. https://www.raspberrypi.org/forums/viewtopic.php?f=66&t=173063&p=1106694#p1106694

Default operation

• By default overlayRoot mounts your root file system read only and overlays a tmpfs ramdisk on top of that. All updates to your system will be lost on power off. Optionally you can specify some media to retain updates across reboots.

• Root is mounted at /ro and tmpfs at /rw

Install

• Copy this directory to a directory on your pi. Change to that directory and run sudo bash install.

git clone https://github.com/marklister/overlayRoot.git
cd overlayRoot
sudo bash install

• Edit /etc/overlayRoot.conf: to suit your preferences. OverlayRoot should work as expected with everything set to default. Options are documented in overlayRoot.conf

• Recommend disabling swapping before using overlayRoot:

sudo dphys-swapfile swapoff
sudo dphys-swapfile uninstall
sudo update-rc.d dphys-swapfile remove

System Maintainence

Disable overlayRoot entirely

• To disable overlayRoot you can jumper the pin specified in the .conf file (default gpio 4) to ground.

• Alternatively edit your cmdline.txt file and place init=/sbin/overlayRoot.sh on a separate line.

Remount

• You can remount the root to make changes: sudo mount -o remount,rw /ro

Chroot

• The chroot command might allow you to install software without reboot:

pi@raspberrypi:~ $ sudo mount -o remount,rw /ro
pi@raspberrypi:~ $ sudo chroot /ro
root@raspberrypi:/# apt update
Get:1 http://archive.raspberrypi.org/debian buster InRelease [25.1 kB]                                             
Get:2 http://raspbian.raspberrypi.org/raspbian buster InRelease [15.0 kB]                                          
Get:3 http://raspbian.raspberrypi.org/raspbian buster/main armhf Packages [13.0 MB]
Get:4 http://archive.raspberrypi.org/debian buster/main armhf Packages [201 kB]                                          
...                                                            
root@raspberrypi:/# exit
exit
pi@raspberrypi:~ $ 

Persistent media

• Enable persistent media by placing an entry in your /etc/fstab. Edit /ro/etc/fstab if overlayRoot is active.

proc                                          /proc          proc    defaults                 0       0
PARTUUID=78a96f0b-01                          /boot          vfat    defaults                 0       2
UUID="d065e631-6b9d-48c0-a8fe-e663b42828e0"   /              ext4    defaults,noatime         0       1
UUID="cf3aa597-5e28-44b2-8dfb-8c21d7312589"   /mnt/root-rw   ext4    defaults,noatime,nofail  0       1

• To obtain UUIDs use the blkid command.

Limitations

• PARTUUIDs are not supported. Use UUIDs instead.
• dphys-swapfile doesn't start on Raspian Buster