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overlayRoot.sh

Read-only Root-FS for most Linux distributions using OverlayFS. Just like the package overlayroot in Ubuntu but it will work on almost all distributions.

Forked from: https://wiki.psuter.ch/doku.php?id=solve_raspbian_sd_card_corruption_issues_with_read-only_mounted_root_partition

Installation

  1. Move this script to /sbin/overlayRoot.sh or other location you want.
  2. chmod +x /sbin/overlayRoot.sh
  3. Change your boot parameter. Add/Modify init=/sbin/init to init=/sbin/overlayRoot.sh.
  4. Reboot and enjoy.

What does it actually do

In general, the script will mount a OverlayFS over the original root file system using tmpfs as upper layer.

  1. Get all useful rootfs information from /etc/fstab.
  2. Mount a tmpfs at /mnt/overlay, create /mnt/overlay/upper, /mnt/overlay/work, /mnt/overlay/newroot.
  3. Bind mount rootfs to /mnt/lower.
  4. Mount OverlayFS using /mnt/lower as lower, /mnt/overlay/upper and /mnt/overlay/work as upper and work directory, /mnt/overlay/newroot as merged destination.
  5. pivot_root to /mnt/overlay/newroot and put old root to /mnt.
  6. Move mount point /mnt/mnt/lower(the original /mnt/lower) to /lower, /mnt/mnt/overlay(the original /mnt/overlay) to /overlay.
  7. Move all other useful virtual filesystems like procfs or devfs to new root.
  8. Unmount /mnt(the original root file system).
  9. Exec /sbin/init and continue the init process.

Compatibility

The upstream project is only compatible with Raspbian and has not been updated for years. Thus I add some patches to make it work on almost all Linux distributions.

It has been tested that it works on:

  • Systemd
  • OpenRC
  • Raspbian
  • Armbian
  • ArchLinux

Notice

  • Do all actions in Installation part with root permissions.
  • To temporary disable overlayRoot.sh, add noOverlayRoot to your kernel parameter.
  • Double-check your /etc/fstab, this script will get rootfs mount point information from it. only UUID, PARTUUID, LABLE and raw device is supported but use PARTUUID remain not recommended.
  • If you use this script and stuck at the emergency shell or something similar, change your boot parameter back.
  • Some distribution is extremely Non-POSIX during init (such as Nix OS). Do not use this script.

Troubleshooting

  • Failed on some distributions whose init executable is not /sbin/init.

FIX: Simply replace all /sbin/init in this script to the value of your distribution use (for example: sed -i 's|/sbin/init|/init|g' overlayRoot.sh).

  • Failed on some distributions doesn't have /etc/fstab or doesn't have it during the very early stage of init.

FIX: Manually add rootfs mount information in your /etc/fstab.

  • Failed on some kernel that not support OverlayFS.

FIX: Use another kernel. Change distribution. etc...

  • Failed on some distributions call main init executable (like systemd/openrc/sysv) in initramfs.

FIX: Move this script to initramfs.