tmpfsroot-fedora

Build power-failure-safe linux image based on Fedora for IoT systems

Basics

How to protect filesystems from power failure

Write operations during power failure may cause filesystem inconsistency. On tmpfsroot-fedora,

• copy rootfs contents to tmpfs during boot and unmount original rootfs
• mount persistent data partitions readonly
• wipe and format broken filesystem during boot (for /var/log)

to keep the system at least bootable and connected to the network.

Why based on Fedora

• Initrd maintainance tools: custom initrd to achieve rootfs-on-tmpfs and filesystem fault handling should be maintained accross base OS upgrades. dracut make it easy and sustainable.
• Fully with systemd: we need init process to be systemd to maintain service dependencies with many hardware devices (from initrd).

Partition structure

Mount point	Size	Filesystem	Usage
/boot/efi	200M	fat32	EFI
/ (A)	2G	ext4	Readonly rootfs (main/fallback)
/ (B)	2G	ext4	Readonly rootfs (main/fallback)
/persist	200M	ext4	Readonly persistent data
/var/log	${PARTSIZE_LOG}	ext4	Logs (automatically refreshed on failure)
/opt	${PARTSIZE_OPT}	btrfs	User applications
/var/cache	${PARTSIZE_CACHE}	btrfs	User cache
/var/lib/docker	${PARTSIZE_DOCKER}	btrfs	Docker

Example

Specify Fedora major version to be used.

export FEDORA_MAJOR=37

Generate rpms.lock

1. Add required packages to packages.list

   cat << EOS > packages.list
   audit
   authselect
   basesystem
   bash
   btrfs-progs
   busybox
   chrony
   container-selinux
   containerd.io
   coreutils
   curl
   dhcp-client
   docker-ce
   docker-ce-cli
   docker-compose
   dosfstools
   e2fsprogs
   efibootmgr
   filesystem
   firewalld
   grub2-efi-x64
   iproute
   kernel
   kernel-core
   kernel-modules
   rootfiles
   setup
   shim-x64
   sudo
   systemd
   EOS

2. Generate rpms.lock from packages.list

   docker run \
     -i --rm \
     -v $(pwd):/work \
     ghcr.io/seqsense/tmpfsroot-fedora-updater:${FEDORA_MAJOR}

Add files and scripts

Directory	Files	Note
ks	ks.root.cfg	[Required] Kickstart script included to root section
ks	ks.pre-install.cfg	Kickstart script included to %pre-install section
ks	ks.post-nochroot.cfg	Kickstart script included to %post --nochroot section
ks	ks.post.cfg	Kickstart script included to %post section
build-hooks.d	*.sh	Executed before creating ISO
hooks.d	*.sh	Executed during installation
iso-root.override	**/*	Copied to installer disk root
root.override	**/*	Copied to installed filesystem root

Generate installer ISO

export DISK_DEVS=sda,sdb     # System has /dev/sda and /dev/sdb
export MAIN_DISK=sda         # Install OS to /dev/sda
export PARTSIZE_DOCKER=8192  # 8G
export PARTSIZE_LOG=2048     # 2G
export PARTSIZE_CACHE=4096   # 4G
export PARTSIZE_OPT=2048     # 2G

export CACHE_DIR=${HOME}/.cache/tempfsroot-fedora

docker run -i --rm \
  -v "${CACHE_DIR}/.dnf:/var/cache/dnf" \
  -v "${CACHE_DIR}/downloads:/work/downloads" \
  -v "path/to/build-hooks.d:/work/build-hooks.d:ro" \
  -v "path/to/hooks.d:/work/hooks.d:ro" \
  -v "path/to/iso-root.override:/work/iso-root.override:ro" \
  -v "path/to/root.override:/work/root.override:ro" \
  -v "path/to/ks:/work/ks:ro" \
  -v "path/to/packages.list:/work/packages.list:ro" \
  -v "path/to/rpms.lock:/work/rpms.lock:ro" \
  -v "path/to/output:/work/output" \
  -e DISK_DEVS \
  -e MAIN_DISK \
  -e PARTSIZE_DOCKER \
  -e PARTSIZE_LOG \
  -e PARTSIZE_CACHE \
  -e PARTSIZE_OPT \
  ghcr.io/seqsense/tmpfsroot-fedora-builder:${FEDORA_MAJOR}

References

• Kickstart

License

Unless otherwise noted, the sources are licensed under Apache License Version 2.0.