Ubuntu iso customization with a different kernel version, hangs on initramfs

Question

I am trying to build a customized ubuntu iso based on ubuntu Bionic Beaver :

129292a182136a35e1f89c586dbac2e2  ubuntu-18.04-desktop-amd64.iso

I followed this tutorial : https://help.ubuntu.com/community/LiveCDCustomization I chrooted into the extracted squashfs and installed some debian packets I wanted, downloaded a new kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.15.3/, the launched the mkinitramfs -o /initrd.gz 4.15.3-041503-generic command.

Then I used the following commands to rebuild the iso:

sudo rm -f iso/casper/vmlinuz iso/casper/initrd.lz
sudo cp squashfs/boot/vmlinuz-4.15.3-041503-generic iso/casper/vmlinuz 
sudo cp squashfs/initrd.gz iso/casper/initrd.lz
sudo chmod a+w iso/casper/filesystem.manifest
sudo chroot squashfs dpkg-query -W --showformat='${Package} ${Version}\n' > iso/casper/filesystem.manifest
sudo chmod go-w iso/casper/filesystem.manifest
sudo rm iso/casper/filesystem.squashfs
cd squashfs
sudo mksquashfs . ../iso/casper/filesystem.squashfs -info
cd ..
cd iso
sudo bash -c "find . -path ./isolinux -prune -o -type f -not -name md5sum.txt -print0 | xargs -0 md5sum | tee md5sum.txt"
cd ..
sudo mkisofs -r -V "my_custom_iso" -cache-inodes -J -l -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -o custom-livecd.iso iso 
sudo isohybrid custom-livecd.iso

I tried to boot virtualbox on the newly created iso, it seems to work since I can see the splash screen of ubuntu loading but then it hangs on the initramfs shell :

Answer 1

This is the code for the message:

 # Confirm the final format was valid.
    if [ "${UNIONFS}" != "unionfs-fuse" ]; then
        modprobe "${MP_QUIET}" -b "${UNIONFS}" || true
        if cut -f2 /proc/filesystems | grep -q "^${UNIONFS}\$"; then
            :
        else
            panic "/cow format specified as ${UNIONFS} and no support found"
        fi
    fi

• 1st IF is always true.
• 2nd IF: if union-fs can not be found in /proc/filesystems error notice.
• Basically you are missing an overlay
• Seems to be a bug in Casper 1.34+

Fix:

• edit /shared/livecd/work/rootfs/etc/initramfs-tools/modules
• add overlay.ko
• run update-initramfs -u -k $(uname -r)