My understanding is that the UEFI/BIOS will boot into a certain storage device, whether it be HDD, SSD, USB, DVD, etc. Then this will pass control to the boot-loader, which is GRUB in Linux operating systems. (additional question: do other Linux OS's require different bootstrap loaders?)

Does GRUB load an OS from a specific partition on the drive? If so, how can I direct it to boot from a specific partition? Will installing certain ISOs in certain partitions using GParted work? I am currently running Ubuntu on a USB SD Card Reader with a MicroSD card temporarily.

  • so just bear with me ...... +1 for spelling "bear" correctly ... the question is also a good one – jsotola Jan 8 at 2:25
  • GRUB is able to boot any linux kernel stored on almost any filesystem. Then OS booting process is handled by the kernel itself. What do you mean by "direct it to boot from a specific partition"? – 炸鱼薯条德里克 Jan 8 at 2:27
  • I'm not exactly sure how GRUB knows where the OS is located, so I assumed it would locate the correct partition on the drive to load the OS from. I'm not sure how GPT cooperates with GRUB, and I'm not sure where GRUB is located -- whether it's stored in its own partition or not. Help with that would also be useful and appreciated if necessary to know for my main question. – TheRyGuy Jan 8 at 3:03
  • I figured you could have multiple partitions with a different OS in each one and tell GRUB to load data from a specific partition. – TheRyGuy Jan 8 at 3:36
  • The usual way this works is that grub loads a grub.cfg script which is generated. This is a script which loads a kernel from devices which are specified like hd(1,gpt4)/boot/wibble to specify the file /boot/wibble from 4th partition in a disk formatted with a gpt partition on the second disk. This script is frequently available in /boot/grub/grub.cfg. The script can get grub to put up menus to select different partitions and versions. – icarus Jan 8 at 6:14

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