Part 3: Install Ubuntu (or Debian) along Ventoy in VHD files

NOTE: this does not use the Ventoy Linux vDisk Boot Plugin. See the FAQ why.

Step 1: Create the Ubuntu VM

Run VirtualBox

  • New virtual machine
  • Name it VentUbuntu
  • For VM folder, use the "VentMore" partition (VirtualBox will create a directory "VentUbuntu")
  • Use unattended setup for convenience
  • Set preferred username, password, host and domain name
  • Do not auto-install guest additions - at the time of writing the script is broken and will cause an error after installation, guest integration is mostly preinstalled anyways
  • Change virtual disk type to VHD, check "pre-allocate full size"
  • Make it 30 GiB or bigger in size
  • Finish, wait for the install to complete, shutdown the VM

Step 2: Move the bootloader to VentUbuntuBoot.vhd

Run VirtualBox

  • Add a virtual disk: 1 GiB VentUbuntuBoot.vhd, pre-allocated, located along VentUbuntu.vhd.
  • Re-order the disks to be
    • VentUbuntuBoot.vhd on port 0
    • VentUbuntu.vhd on port 1

At this point, the VM is only bootable with the VirtualBox boot menu

  • Boot the VM, press F12, select disk 2 to boot

In the booted VM in a terminal

  • lsblk # Verify you see the new disk sda = 1 GiB
  • sudo parted /dev/sda # create boot partitions
    mklabel gpt
mkpart bios_boot 1MiB 3MiB
set 1 bios_grub on
mkpart boot 3MiB 100%
  • sudo e2label /dev/sdb2 VentUbuntuRoot # For easier referencing, label the rootfs
  • sudo mkfs.ext4 -L VentUbuntuBoot /dev/sda2 # Format the new home for /boot
  • sudo mkdir -p /tmp/mntBoot && sudo mount LABEL=VentUbuntuBoot /tmp/mntBoot # Mount it
  • sudo cp -ax /boot/* /tmp/mntBoot # Copy the current /boot
  • ls /tmp/mntBoot # Verify the filesystem holds vmlinuz, initrd.img
  • sudo editor /etc/fstab # Add the following line to fstab
    /dev/disk/by-label/VentUbuntuBoot /boot ext4 defaults,x-systemd.automount 0 2
  • sudo mv /boot /boot.old # Rename the old /boot so it is never considered for updates
  • sudo mkdir /boot && sudo chattr +i /boot # Create an immutable dir for mountpoint
  • sudo systemctl daemon-reload && sudo systemctl restart boot.automount # Load the automounter
  • ls /boot # Verify the automount works and vmlinuz, initrd.img are present
  • sudo update-grub # Update the GRUB config
  • sudo grub-install /dev/sda # Update the GRUB bootloader

Reboot the VM to verify it boots fine (no need to switch disk with F12)

Step 3: Open VHD files at boot

We add scripts to open the VHD files in the initial ramdisk which is directly loaded by GRUB. The standard boot process can pick up from there.

Determine what tooling your distro chose to install (default since Ubuntu 25.10 is Dracut):

Open VHD files at boot: Variant for initramfs-tools

Make kpartx available in initramfs:

  • sudo apt install kpartx
  • sudo editor "/etc/initramfs-tools/hooks/VentUbuntuVHD" 
    #!/bin/sh
PREREQ=""
. /usr/share/initramfs-tools/hook-functions

copy_exec /sbin/kpartx /sbin
  • sudo chmod +x "/etc/initramfs-tools/hooks/VentUbuntuVHD"

Make exFAT available in initramfs:

  • sudo editor "/etc/initramfs-tools/modules"
    # Required for VHD losetup
exfat

This initramfs "top" phase script will mount the exFAT partitions Ventoy and VentMore and losetup the VHD files

  • sudo editor "/etc/initramfs-tools/scripts/local-top/VentUbuntuVHD" 
    #!/bin/sh

case $1 in
prereqs)
  exit 0
  ;;
esac

echo -n "Waiting for boot files to be available ..."
while [ ! -e "/dev/disk/by-label/VentMore" ]; do
  if [ -e "/dev/disk/by-label/VentUbuntuBoot" ]; then
    echo " no need to losetup VHDs, continue boot"
    exit 0
  fi
  sleep 1
  echo -n "."
done
echo ""

echo "Mount VentMore ..."
mkdir -p "/mnt/VentMore"
mount -t exfat -o uid=1000,gid=1000 "/dev/disk/by-label/VentMore" "/mnt/VentMore"

echo "Mount Ventoy ..."
mkdir -p "/mnt/Ventoy"
mount -t exfat -o uid=1000,gid=1000 "/dev/disk/by-label/Ventoy" "/mnt/Ventoy"

echo "losetup VHD files ..."
loboot=$(losetup -f)

# Expecting the /boot VHD on either partition
if [ -e "/mnt/VentMore/VentUbuntu/VentUbuntuBoot.vhd" ]
then
  losetup "$loboot" "/mnt/VentMore/VentUbuntu/VentUbuntuBoot.vhd"
else
  losetup "$loboot" "/mnt/Ventoy/VentUbuntu/VentUbuntuBoot.vhd"
fi
kpartx -a "$loboot"

loroot=$(losetup -f)
losetup "$loroot" "/mnt/VentMore/VentUbuntu/VentUbuntu.vhd"
kpartx -a "$loroot"

# From this point on, the standard scripts can see and mount / and /boot
  • sudo chmod +x "/etc/initramfs-tools/scripts/local-top/VentUbuntuVHD"

The following "bottom" phase script will move the extfs mount from initramfs to rootfs

  • sudo editor "/etc/initramfs-tools/scripts/local-bottom/VentUbuntuVHD" 
    #!/bin/sh
case $1 in
prereqs)
        exit 0
        ;;
esac

# Move the mounts so they can be re-used
mount --move "/mnt/VentMore" "/root/mnt/VentMore"
mount --move "/mnt/Ventoy" "/root/mnt/Ventoy"
  • sudo chmod +x "/etc/initramfs-tools/scripts/local-bottom/VentUbuntuVHD"
  • sudo mkdir "/mnt/VentMore" && sudo chattr +i "/mnt/VentMore" # Create destinations
  • sudo mkdir "/mnt/Ventoy" && sudo chattr +i "/mnt/Ventoy"
  • sudo update-initramfs -u -k all # Update the initramfs

For a clean shutdown, the VHD housing filesystems must be closed. initramfs-tools provides no infrastructure for this, so we use this rather hacky approach to force all filesystems read-only. Note that rootfs already is read-only at this stage and the only realistically affected fs should be the ones backing our loop devices, which are then clean for poweroff.

  • sudo editor "/lib/systemd/system-shutdown/VentUbuntuVHD.shutdown" 
    #!/bin/sh

# force leftover filesystems into read-only
echo s > /proc/sysrq-trigger
echo u > /proc/sysrq-trigger
  • sudo chmod +x "/lib/systemd/system-shutdown/VentUbuntuVHD.shutdown"

Done. Skip to step 4.

Open VHD files at boot: Variant for Dracut

Create a dracut module:

  • sudo mkdir /usr/lib/dracut/modules.d/99ventubuntu
  • sudo editor /usr/lib/dracut/modules.d/99ventubuntu/module-setup.sh 
    #!/bin/bash

check() {
    return 0
}

depends() {
    echo "rootfs-block"
    # return 0 installs module by default
    return 0
}

installkernel() {
    hostonly='' instmods -c exfat
}

install() {
    inst_hook initqueue/settled 10 "$moddir/ventubuntu-vhd.sh"
    inst_hook pre-pivot 10 "$moddir/ventubuntu-mntmove.sh"
}
  • sudo chmod +x /usr/lib/dracut/modules.d/99ventubuntu/module-setup.sh

Script mounting the exfat filesystems:

  • sudo editor /usr/lib/dracut/modules.d/99ventubuntu/ventubuntu-vhd.sh 
    #!/bin/sh

# user and group IDs for the mounted USB volumes
MNT_UID=1000
MNT_GID=1000

# mount present USB volumes
usb_mount() {
  if [ -e "$1" ] && [ ! -e "$2" ]; then
      mkdir -p "$2"
      mount -o uid=$MNT_UID,gid=$MNT_GID "$1" "$2"
  fi
}

usb_mount "/dev/disk/by-label/Ventoy" "/mnt/Ventoy"
usb_mount "/dev/disk/by-label/VentMore" "/mnt/VentMore"

# search and losetup VHD files
vhd_search() {
  if [ ! -e "$1" ]; then
      # blockdevice is missing, search for VHD
      if [ -e "/mnt/VentMore/$2" ]; then
          losetup -Pf "/mnt/VentMore/$2"
          need_shutdown
      elif [ -e "/mnt/Ventoy/$2" ]; then
          losetup -Pf "/mnt/Ventoy/$2"
          need_shutdown
      fi
  fi
}

vhd_search "/dev/disk/by-label/VentUbuntu" "VentUbuntu/VentUbuntu.vhd"
vhd_search "/dev/disk/by-label/VentUbuntuBoot" "VentUbuntu/VentUbuntuBoot.vhd"
  • sudo chmod +x /usr/lib/dracut/modules.d/99ventubuntu/ventubuntu-vhd.sh

Script to move the mounts into the rootfs:

  • sudo editor /usr/lib/dracut/modules.d/99ventubuntu/ventubuntu-mntmove.sh 
    #!/bin/sh

mntmove() {
    if [ -e "$1" ]; then
        mount --bind "$1" "${NEWROOT}$1"
    fi
}

mntmove "/mnt/Ventoy"
mntmove "/mnt/VentMore"
  • sudo chmod +x /usr/lib/dracut/modules.d/99ventubuntu/ventubuntu-mntmove.sh
  • sudo mkdir "/mnt/Ventoy" "/mnt/VentMore" # Create destinations
  • sudo chattr +i "/mnt/Ventoy" "/mnt/VentMore"
  • sudo update-initramfs -u -k all # Update the initramfs

Step 4: Customize GRUB inside and outside VM boot mode

Inside the VM, we simplify the GRUB search, too, so update-grub cannot get confused:

  • sudo editor "/etc/grub.d/07-VentUbuntu" 
    #!/bin/sh
set -e

cat << 'EOF'
# Ubuntu
set ubuntu_cmdline="root=LABEL=VentUbuntuRoot ro net.ifnames=0 biosdevname=0"
set ubuntu_cmdline_recovery="$ubuntu_cmdline recovery nomodeset dis_ucode_ldr"
search --no-floppy --set ubuntu_bootfs --label VentUbuntuBoot

menuentry "VentUbuntu" {
  set root=($ubuntu_bootfs)
  linux	/vmlinuz $ubuntu_cmdline
  initrd	/initrd.img
}
menuentry "VentUbuntu (recovery mode, old kernel)" {
  set root=($ubuntu_bootfs)
  linux	/vmlinuz.old $ubuntu_cmdline_recovery
  initrd	/initrd.img.old
}
EOF
  • sudo chmod +x "/etc/grub.d/07-VentUbuntu"
  • sudo update-grub # Update the grub config on the 1 GiB disk

Reboot the VM to verify the custom boot menu works. Shutdown the VM.

On host:

  • Create a directory ventoy on the Ventoy partition
  • Edit or create /ventoy/ventoy_grub.cfg and add this: 
    # Ubuntu
set ubuntu_cmdline="root=LABEL=VentUbuntuRoot ro net.ifnames=0 biosdevname=0"
set ubuntu_cmdline_recovery="$ubuntu_cmdline recovery nomodeset dis_ucode_ldr"
set ubuntu_vhd_path="VentUbuntu/VentUbuntuBoot.vhd"
set ubuntu_vhd_partname="VentMore"
search --no-floppy --set ubuntu_vhd_part --label $ubuntu_vhd_partname
menuentry "VentUbuntu" {
  loopback loop9 ($ubuntu_vhd_part)/$ubuntu_vhd_path
  set root=(loop9,2)
  linux	/vmlinuz $ubuntu_cmdline
  initrd	/initrd.img
}
menuentry "VentUbuntu (recovery mode, old kernel)" {
  loopback loop9 ($ubuntu_vhd_part)/$ubuntu_vhd_path
  set root=(loop9,2)
  linux	/vmlinuz.old $ubuntu_cmdline_recovery
  initrd	/initrd.img.old
}

USB boot to verify the custom Ventoy menu works (access via F6).

(Optional) Step 5: Move VentUbuntuBoot.vhd to the Ventoy partition

If you need to boot Ubuntu on a BIOS which can only access the first partition, you can move VentUbuntuBoot.vhd and adjust the Ubuntu part of the ventoy_grub.cfg. Say you create a matching directory VentUbuntu, these two lines must match:

set ubuntu_vhd_path="VentUbuntu/VentUbuntuBoot.vhd"
set ubuntu_vhd_partname="Ventoy"

The VirtualBox VM unfortunately becomes less portable in this case because the location of VentUbuntuBoot.vhd is no longer relative to the .vboxfile but an absolute path. A workaround is to copy over the VentUbuntuBoot.vhd whenever needed and only temporarily make this change. Or have the entire VentUbuntu directory reside on the Ventoy partition, taking up a significant amount of the 120 GiB partition.

Up next: FreeDOS

Continue with Part 4: Install FreeDOS along Ventoy in VHD files