#!/bin/sh
# Read-only Root-FS for Raspian using overlayfs
# Version 1.1
#
# Version History:
# 1.0: initial release
# 1.1: adopted new fstab style with PARTUUID. the script will now look for a /dev/xyz definiton first
# (old raspbian), if that is not found, it will look for a partition with LABEL=rootfs, if that
# is not found it look for a PARTUUID string in fstab for / and convert that to a device name
# using the blkid command.
#
# Created 2017 by Pascal Suter @ DALCO AG, Switzerland to work on Raspian as custom init script
# (raspbian does not use an initramfs on boot)
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see
# .
#
#
# Tested with Raspbian mini, 2018-10-09
#
# This script will mount the root filesystem read-only and overlay it with a temporary tempfs
# which is read-write mounted. This is done using the overlayFS which is part of the linux kernel
# since version 3.18.
# when this script is in use, all changes made to anywhere in the root filesystem mount will be lost
# upon reboot of the system. The SD card will only be accessed as read-only drive, which significantly
# helps to prolong its life and prevent filesystem coruption in environments where the system is usually
# not shut down properly
#
# Install:
# copy this script to /sbin/overlayRoot.sh, make it executable and add "init=/sbin/overlayRoot.sh" to the
# cmdline.txt file in the raspbian image's boot partition.
# I strongly recommend to disable swapping before using this. it will work with swap but that just does
# not make sens as the swap file will be stored in the tempfs which again resides in the ram.
# run these commands on the booted raspberry pi BEFORE you set the init=/sbin/overlayRoot.sh boot option:
# sudo dphys-swapfile swapoff
# sudo dphys-swapfile uninstall
# sudo update-rc.d dphys-swapfile remove
#
# To install software, run upgrades and do other changes to the raspberry setup, simply remove the init=
# entry from the cmdline.txt file and reboot, make the changes, add the init= entry and reboot once more.
fail(){
echo -e "$1"
/bin/bash
}
# load module
modprobe overlay
if [ $? -ne 0 ]; then
fail "ERROR: missing overlay kernel module"
fi
# mount /proc
mount -t proc proc /proc
if [ $? -ne 0 ]; then
fail "ERROR: could not mount proc"
fi
# create a writable fs to then create our mountpoints
mount -t tmpfs inittemp /mnt
if [ $? -ne 0 ]; then
fail "ERROR: could not create a temporary filesystem to mount the base filesystems for overlayfs"
fi
mkdir /mnt/lower
mkdir /mnt/rw
mount -t tmpfs root-rw /mnt/rw
if [ $? -ne 0 ]; then
fail "ERROR: could not create tempfs for upper filesystem"
fi
mkdir /mnt/rw/upper
mkdir /mnt/rw/work
mkdir /mnt/newroot
# mount root filesystem readonly
rootDev=`awk '$2 == "/" {print $1}' /etc/fstab`
rootMountOpt=`awk '$2 == "/" {print $4}' /etc/fstab`
rootFsType=`awk '$2 == "/" {print $3}' /etc/fstab`
echo "check if we can locate the root device based on fstab"
blkid $rootDev
if [ $? -gt 0 ]; then
echo "no success, try if a filesystem with label 'rootfs' is avaialble"
rootDevFstab=$rootDev
rootDev=`blkid -L "rootfs"`
if [ $? -gt 0 ]; then
echo "no luck either, try to further parse fstab's root device definition"
echo "try if fstab contains a PARTUUID definition"
echo "$rootDevFstab" | grep 'PARTUUID=\(.*\)-\([0-9]\{2\}\)'
if [ $? -gt 0 ]; then
fail "could not find a root filesystem device in fstab. Make sure that fstab contains a device definition or a PARTUUID entry for / or that the root filesystem has a label 'rootfs' assigned to it"
fi
device=""
partition=""
eval `echo "$rootDevFstab" | sed -e 's/PARTUUID=\(.*\)-\([0-9]\{2\}\)/device=\1;partition=\2/'`
rootDev=`blkid -t "PTUUID=$device" | awk -F : '{print $1}'`p$(($partition))
blkid $rootDev
if [ $? -gt 0 ]; then
fail "The PARTUUID entry in fstab could not be converted into a valid device name. Make sure that fstab contains a device definition or a PARTUUID entry for / or that the root filesystem has a label 'rootfs' assigned to it"
fi
fi
fi
mount -t ${rootFsType} -o ${rootMountOpt},ro ${rootDev} /mnt/lower
if [ $? -ne 0 ]; then
fail "ERROR: could not ro-mount original root partition"
fi
mount -t overlay -o lowerdir=/mnt/lower,upperdir=/mnt/rw/upper,workdir=/mnt/rw/work overlayfs-root /mnt/newroot
if [ $? -ne 0 ]; then
fail "ERROR: could not mount overlayFS"
fi
# create mountpoints inside the new root filesystem-overlay
mkdir /mnt/newroot/ro
mkdir /mnt/newroot/rw
# remove root mount from fstab (this is already a non-permanent modification)
grep -v "$rootDev" /mnt/lower/etc/fstab > /mnt/newroot/etc/fstab
echo "#the original root mount has been removed by overlayRoot.sh" >> /mnt/newroot/etc/fstab
echo "#this is only a temporary modification, the original fstab" >> /mnt/newroot/etc/fstab
echo "#stored on the disk can be found in /ro/etc/fstab" >> /mnt/newroot/etc/fstab
# change to the new overlay root
cd /mnt/newroot
pivot_root . mnt
exec chroot . sh -c "$(cat <