Live debian USB stick with debootstrap, squashfs and grub

Question

I want to create my own Debian Live boot stick from a chroot (debootstrap) environment.

The root filesystem should be mounted as squashfs and grub should be able to boot the system from a single EFI partition.

So far, I have a squashfs image of the chroot environment, vmlinuz and initrd.img on the stick. However, I don't know, how I have to configure grub so that it doesn't boot my local system (tried with: grub-install...) but instead the squashfs of the USB stick.

Answer 1

I solved the problem!

First, the chroot environment must have the necessary initframes to load a shquashfs image. For this, I simply installed the live boot packet in the chroot and then updated the initframes. /proc, /dev/pts, /dev, /sys should be available in the chroot for this to work.

# @ root on localhost
mount -o bind /proc /debootstrap/proc
mount -o bind /dev /debootstrap/dev
mount -o bind /dev/pts /debootstrap/dev/pts
mount -o bind /sys /debootstrap/sys

# @ root in chroot
apt install live-boot live-boot-initramfs-tools
update-initramfs -u

When that is done, these directories should be unmounted and the shquashfs can be created to /target/live/filesystem.squashfs.

# @ root on localhost
umount /debootstrap/proc
umount /debootstrap/dev
umount /debootstrap/dev/pts
umount /debootstrap/sys

# @ root on localhost
mksquashfs -comp xz /debootstrap /target/live/filesystem.squashfs

I formatted the USB stick in fat32 and mounted it in /target. Now Grub can be installed.

# @ root on localhost
grub-install --target=x86_64-efi --root-directory=/target

Once that's done, copy vmlinuz and the initrd.img to /target/boot and create the grub.cfg in /target/boot/grub/grub.cfg with the following contend.

insmod all_video

set default=0
set timeout=0

menuentry "debian live" {
    linux /boot/vmlinuz boot=live toram=filesystem.squashfs quiet
    initrd /boot/initrd.img
}

This is it, your pc should be able to EFI boot this stick.