The demo was performed on a QEMU virtual machine using BIOS+GPT with Ubuntu 22.04 OS installed.

qemu-system-x86_64 -cpu host -enable-kvm \\
-hda ubuntu.qcow2 -hdb erofs.qcow2 \\
-net user,hostfwd=tcp::10022-:22 -net nic \\
-smp 16 -m 8G

  1. Firstly, let’s compile and install our modified GRUB bootloader.

    cd ~/grub-latest

# compile GRUB
./bootstrap
./configure --prefix=~/grub-latest/install --target=x86_64
make -j20
make install

# install GRUB
cd install
sudo ./sbin/grub-install --target=i386-pc /dev/sda
sudo ./sbin/grub-mkconfig -o /boot/grub/grub.cfg

    Note that the version number has changed to 2.12-rc1.

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  2. Prepare virtual disk for EROFS partition

    >sudo fdisk /dev/sdb
Command (m for help): g
Created a new GPT disklabel (GUID: 1FB769D1-08CD-8F45-A651-5F3A8CB16729).

Command (m for help): n
Partition number (1-128, default 1): 
First sector (2048-20971486, default 2048): 
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-20971486, default 20971486): 

Created a new partition 1 of type 'Linux filesystem' and of size 10 GiB.

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

  3. Pack vmlinuz and initrd into EROFS partition /dev/sdb

    mkdir ~/erofs-src
sudo cp /boot/*5.19.0-45* ~/erofs-src/

>ls ~/erofs-src
config-5.19.0-45-generic  initrd.img-5.19.0-45-generic  System.map-5.19.0-45-generic  vmlinuz-5.19.0-45-generic

sudo mkfs.erofs /dev/sdb1 ~/erofs-src/

    Make sure we are doing the correct things…

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  4. Add a GRUB custom boot entry, modify ~/grub-latest/install/etc/grub.d/40_custom

    #!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.

menuentry "Test" {
        linux (hd1,1)/vmlinuz-5.19.0-45-generic root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX ro
        initrd (hd1,1)/initrd.img-5.19.0-45-generic
}

  5. update /boot/grub/grub.cfg

    sudo ./sbin/grub-mkconfig -o /boot/grub/grub.cfg

  6. Selecting the “Test” entry in GRUB, and we successfully enter the Desktop.

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