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This answer explains the output of efibootmgr -v, and with repect to the following lines:

Boot0003* ATA HDD2: WDC WD5000LPVT-08G33T1                      ACPI(a0341d0,0)PCI(1f,2)03120a00010000000000..bYVD.A...O.*..
Boot0004* ATA SSD1: SanDisk SSD U100 24GB                       ACPI(a0341d0,0)PCI(1f,2)03120a00000000000000..bYVD.A...O.*..

It states that:

In most cases, when you see an entry like this that refers to a disk device, the reference is really to the fallback boot loader file (EFI/BOOT/bootx64.efi, at least on x86-64 systems) on the disk's EFI System Partition (ESP). EFI does not use boot loaders embedded in a disk's MBR, the way BIOS does.

And I was wondering about my case: I have a new PC with Windows pre-insatlled (This is a UEFI machine of course). I wanted to install Ubuntu, so I created a Live-CD on a USB, restarted the computer with the USB inside, and Ubuntu was booted so I could install it. That USB has no EFI partition, and the boot was probably from the MBR code, (There is MBR code on that Live-CD).

Can someone explain?

YoavKlein
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1 Answers1

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The live media have both the MBR boot record, and UEFI boot capability -- the entire filesystem meets the EFI criteria for a EFI partition, the /EFI directory is the location for the UEFI bootloaders. How your machine is set up in the UEFI settings determines how the live media boots (legacy or UEFI) and how the install is made.

If the bootloaders under /EFI were missing, the MBR boot in legacy mode would still work, but no UEFI boot would be possible. Now that's the ISO's filesystem, one big filesystem -- but some tools used to burn the ISO information to media might create additional partitions, and do might even do bad things like copy parts of the running system onto the newly created install media (causing problems when version mismatches occur). The simple dd byte copy produces a live media just like the ISO.

ubfan1
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