Boot with live Ubuntu session and Ubuntu partition from Windows without a USB and without installing grub

Question

Some users realize that they boot directly to Windows after installing Ubuntu. Also some users have to install Windows after Ubuntu, but this affects the loss of the grub bootloader. When the USB flash drive is lost or corrupted they can't go back to an Ubuntu live session or Ubuntu partition.

Now we have to reach Ubuntu from Windows, but the problem is that Windows prevents us from adding Ubuntu to the boot menu. In addition, Windows can't read the Linux based partitions, and doesn't help to boot from an Ubuntu ISO file.

Most guides recommend using EasyBCD to add the Ubuntu partition to the Windows boot menu, but this doesn't work anymore with the new Ubuntu releases.

For recovery purposes and for dual boot users, it is important to add an Ubuntu live session and or Ubuntu partition to the Windows Boot Manager.

The question is how to boot with Ubuntu from the Windows boot menu?

Update:

The aim is boot by Ubuntu Live Session from squashfs file and Ubuntu partition, this makes difference from other questions existed or suggested. Ubuntu 24.04 desktop version and Windows 11 23h2 are used in bios based device. thanks for sharing your experience.

Answer 1

Adding multi-Ubuntu boot entries to the Windows boot manager

1. Use Bootice.exe to add one entry to the BCD file.

2. Copy the /casper directory from the Ubuntu ISO file to the root of the Windows partition. If you want to install Ubuntu, copy all directories from the ISO file except the boot directory; don't copy the boot directory to the Windows partition.

3. Copy these files; grldr and grldr.mbr from the Easybcd directory to the root of the Windows partition. Bootice.exe and Easybcd.exe exist in HBCD_PE_64.iso and can be downloaded online.

4. Create a menu.lst file in the root of the Windows partition, and add the appropriate entries. this is an example:

timeout 5
default 0
title Ubuntu
kernel /boot/vmlinuz-6.8.0-40-generic root=/dev/sda3 ro --
initrd /boot/initrd.img-6.8.0-40-generic
title \n
root
title Ubuntu 24.04 Live System
kernel /casper/vmlinuz-noble boot=casper layerfs-path=minimal.squashfs --
initrd /casper/initrd-noble
title \n
root
title Ubuntu 22.04 Live System
kernel /casper/vmlinuz boot=casper layerfs-path=filesystem.squashfs --
initrd /casper/initrd.gz

In this example, three entries were added, one for the Ubuntu partition and two for live sessions. When you reboot and select Ubuntu, you will see all these entries in the submenu.

If you use more than one live session, rename the vmlinuz, initrd, and *.sguashfs files in the /casper directory and use the same names in the menu entry. If you want to install Ubuntu, don't rename the files, rename the live session files instead.

Now you can boot with one or more live sessions. To reach the Ubuntu partition, copy the vmlinuz and initrd files from the /boot directory in Ubuntu to the /boot directory in the Windows partition. Also, you can add more kernels.

Now you can use the live session to reinstall the grub bootloader or use boot-repair to solve the auto booting to Windows without the USB flash drive.

Update:

Menu entry to boot from Ubuntu ISO file:

title Boot ubuntu noble iso 
set ISO=/noble-desktop-amd64.iso
find --set-root %ISO%
map %ISO% (0xff)
map --hook
root (0xff)
kernel /casper/vmlinuz boot=casper iso-scan/filename=/noble-desktop-amd64.iso --
initrd /casper/initrd

Menu entry to boot from Super Grub2 Disk ISO file:

title Boot Super Grub2 Disk
find --set-root --ignore-floppies --ignore-cd /super_grub2_disk_hybrid_2.04s1.iso
map --heads=0 --sectors-per-track=0 --mem /super_grub2_disk_hybrid_2.04s1.iso (hd32)
map --hook
root (hd32)
chainloader (hd32)

How to use Windows CMD to boot from the Ubuntu ISO file in the C partition without needing a USB flash drive or creating another partition

Create recovery partition to install, backup, restore and repair: multi Ubuntu versions, HBCD-PE-64 and multi Windows installation without usb drive

Boot to any payload (e.g. linux ISOs) directly from the Windows Boot Manager menu