Assuming that you already have Windows installed on your desktop, you want to install a Ubuntu from a hard disk (NTFS). Before following the instructions bellow, you have installed the bootloader GRUB2 (Search how to install GRUB2 on Windows).
What you need is to create a menuentry in GRUB2. 0. Check your disk partitions in grub: press c and ls to find your partitions.
- (If you have a older version of linux) Append the following menuentry into the file 40_custom at /etc/grub.d/
menuentry "Ubuntu 20.04 install" {
insmod ntfs
insmod iso9660
rmmod tpm #bug for grub2.04, removing module tpm
set root=(hd0,gpt3) #make sure you have the correct partition
#set isofile="/opt/ubuntu-20.04.3-desktop-amd64.iso" #if you put the iso file in the linux partition
set isofile="/Users/setup/Downloads/ubuntu-20.04.3-desktop-amd64.iso" #here we put the iso file at the folder Download
loopback loop $isofile
linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet splash nomodeset noprompt noeject toram --
initrd (loop)/casper/initrd
}- (If you have a older version of linux) Update the grub by
sudo update-grub - Reboot and then you will see the menuentry.