josephvoss / dracut-lazsquash

Dracut module

Mount a local device containing multiple squashfs images. Mount a selected image as the rootfs with a writable ramdisk in overlay.

USB boot stick creation

Right now there's a script that will create and format the partitions needed for boot. Rough partition layout/motivation is shown in the table below. Need a hybrid MBR to support BIOS and UEFI booting.

Name	Size	Purpose
BIOS	1M	Spacer for Hybrid boot partitions (Is this needed? Probably can remove.
ESP	250M	EFI System Partition. Contains rEFInd install for UEFI booting. Configs point to boot files in syslinux.
SYSLINUX	1G	SYSLINUX Install partition. Labeled as boot partition in hybrid MBR, contains kernels and initrd.
IMAGES	6G	Partition containing squashfs images to mount at boot
STATEFUL	Rest of disk	Stateful partition for home mount, containers storage, etc

Modify the parameters and run the script build_usb_syslinux.sh to create these partitions. Afterwards manually create the Hybrid MBR if desired.

$ gdisk /dev/sdc
GPT fdisk (gdisk) version 1.0.5

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

# Enter recovery mode
Command (? for help): r

# Create hybrid MBR
Recovery/transformation command (? for help): h

WARNING! Hybrid MBRs are flaky and dangerous! If you decide not to use one,
just hit the Enter key at the below prompt and your MBR partition table will
be untouched.

# Use the BIOS, ESP, and SYSLINUX martitions
Type from one to three GPT partition numbers, separated by spaces, to be
added to the hybrid MBR, in sequence: 1 2 3
Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): N

Creating entry for GPT partition #1 (MBR partition #1)
Enter an MBR hex code (default EF):
Set the bootable flag? (Y/N): n

Creating entry for GPT partition #2 (MBR partition #2)
Enter an MBR hex code (default EF):
Set the bootable flag? (Y/N): n

# Set syslinux as bootable
Creating entry for GPT partition #3 (MBR partition #3)
Enter an MBR hex code (default 83):
Set the bootable flag? (Y/N): y

# Enter expert mode
Recovery/transformation command (? for help): x

# Regenerate disk hashes
Expert command (? for help): h

# Write to disk
Expert command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT) to /dev/sdc.
The operation has completed successfully.

What's a Hybrid MBR?

New partition table (GPT) supports >4 partitions and a bunch of other neat features. However, older firmware (mostly BIOS boots) only can read the older partition table format (MBR). To support >4 partitions and BIOS booting we need to create a GPT partition table that can also be read as an MBR table.

GPT normally includes a protective MBR table, which is read and marks the entire disk as a single partition. This is to prevent GPT-unaware systems from overwriting a valid GPT disk. We can edit this protective MBR to point to the actual GPT partitions that we need at boot. Caution: This removes the default protection on the rest of the GPT disk, so be aware the modified MBR table does not accurately describe the disk. However this allows a GPT-unaware system to access some of the partitions defined in the GPT table.

Add images to USBs

First, build the image locally by running the scripts in image_builds. Once the image is saved to a container storage, add the image name and tag to add_image_usb.sh, then run the script. This will download the image, mount it on the host filesystem, mount the USB device, and make a squashfs image on the USB mount.

Historical notes

Following arch guide from here.

Grub looks like much more of a pain to maintain and set up for a diskless boot. Using syslinux for bios boots and gummi/systemd boot for efi

How do multiple bootloaders? I think efi is always read for uefi boot, and boot flag is read for MBR.

Planned partitions

GPT: BIOS, EF02, 1MiB EFI, EF00/FAT32, 1G (Systemd-boot uefi. kernels?) KERNELS, (syslinux install, kernels?), bootable flag IMAGES, (dir to mount)

How to join EFI and BIOS kernels? rEFInd can boot point to a different mount point, so have an only rEFIind partition that points to syslinux?

Create GPT partitions above 1: +1M, EF02, BIOS 2: +1G, EF00, ESP 3: +1G, 8300, SYSLINUX 4: +6G, 8300, IMAGES 5: +6G, 8300, STATEFUL Write to disk

add hybrid MBR gdisk /dev/sdd r (recovery mode) h (hybrid MBR) 1 2 3 (first 3 partitions) EPI GT first? N 1 Bootable? N 2 Bootable? N 3 Bootable? Y x (experts) h (re-write hashes) w (write disk)

Format partitions ESP - FAT32 mkfs.fat -F32 /dev/sdd2 SYSLINUX - FAT32 mkfs.fat -F32 /dev/sdd3 IMAGES/STATEFUL - ext4 for i in $(seq 4 5); do mkfs.ext4 /dev/sdd$i ; done e2label /dev/{} {}

Syslinux install

syslinux /dev/sdd3
mount /dev/sdd3 /mnt
cp syslinux.cfg /mnt/
umount /mnt
fatlabel /dev/sdd3 SYSLINUX

Nothing happened until I added mbr boot code to the start of the disk. I guess this is why the BIOS partition exists, but man this is scary

Refind install

mount /dev/disk/by-partlabel/ESP /mnt
mkdir /mnt/EFI/refind
cp /usr/share/refind/refind_x64.efi /mnt/EFI/refind
mkdir /mnt/EFI/BOOT
cp /usr/share/refind/refind_x64.efi /mnt/EFI/BOOT
# Add drivers
mkdir /mnt/EFI/refind/drivers_x64
cp /usr/share/refind/drivers_x64/* /mnt/EFI/BOOT/drivers_x64/

# Install config
cp refind.conf /mnt/EFI/refind/refind.conf
umount /mnt

Install kernels

mount /dev/sdd3
cp ...
umount /dev/sdd3

Building image for aarch64

Refs

• Hybrid MBRs, by Rod Smith
• Multiboot USB guide from Arch Wiki.