Patching Debian 11 and 12 iso images to be Xen HVM compatible

The Debian 11 and Debian 12 iso images have an installer that can crash when started in a HVM configured Xen virtual machine.

Here is a small tutorial how to patch the iso image to be installable. You need a linux environment and need to have the xorriso and initramfs-tools packages installed.

1. Mount the original iso.

   mkdir CD sudo mount -o ro -t iso9660 debian-11.0.0-amd64-netinst.iso CD

2. Copy the initrd.gz file that needs to modification to your local folder.

   cp -p CD/install.amd/initrd.gz .

3. Unmount the iso again.

   sudo umount CD

4. Extract the initramfs directory.

   sudo unmkinitramfs initrd.gz initramfs

5. Edit the start-udev script.

   sudo vi initramfs/lib/debian-installer/start-udev

6. Re-pack the initrd.

   cd initramfs find . | sort | sudo cpio --reproducible --quiet -o -H newc > ../newinitrd cd .. gzip -v9f newinitrd

7. Create the patched installation iso.

   cp -p debian-11.0.0-amd64-netinst.iso debian-11.0.0-amd64-xenhvm-netinst.iso xorriso -dev debian-11.0.0-amd64-xenhvm-netinst.iso -boot_image any keep -map newinitrd.gz /install.amd/initrd.gz

    

8. Clean up (optional).

   sudo rm -r initramfs newinitrd.gz initrd.gz

This tutorial is based on a post from the debian-user list:
https://lists.debian.org/debian-user/2021/08/msg01339.html