Basic question regarding UEFI

[geohei]

I did quite some fiddling around UEFI and efibootmgr, but one of the things I missed is the "link" between the bootmanager (grubx64.efi) and the partition the system resides.

Example (yes, I know ... 2 ESPs - for testing!):


...
Command (? for help): p
Disk /dev/sda: 500118192 sectors, 238.5 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): 7B0E6510-D248-42E6-BB41-8F1545A740AA
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 500118158
Partitions will be aligned on 2048-sector boundaries
Total free space is 38072941 sectors (18.2 GiB)

Number Start (sector) End (sector) Size Code Name
1 2048 206847 100.0 MiB EF00 EFI System - Windows
2 206848 468991 128.0 MiB 0C01 Microsoft reserved part
3 468992 210184191 100.0 GiB 0700 Basic data partition
4 210184192 315041791 50.0 GiB 0700 Basic data partition
5 315041792 315246591 100.0 MiB EF00 EFI System - Ubuntu
6 315246592 420104191 50.0 GiB 0700 Ubuntu
7 420104192 462047231 20.0 GiB 8200 Linux swap

To make an entry into UEFI boot manager, I use:


efibootmgr -c -d /dev/sda -p 5 -l "\EFI\ubuntu\grubx64.efi" -L "Ubuntu"

How does grubx64.efi (located in sda5) know that it should continue to boot in sda6 (which resides the Linux on an ext4 filesystem)?

[oldfred]

You can only have one efi partition per drive. Not sure what happens with two?

I do not know details of efibootmgr, but I would think you still have to install grub from Ubuntu. The boot manager is just adding a boot entry into the UEFI memory.

Launch EFI Shell from File System Device
https://wiki.archlinux.org/index.php/Unified_Extensible_Firmware_Interface#UEFI_Shell
http://software.intel.com/en-us/articles/efi-shells-and-scripting/


http://linux.die.net/man/8/efibootmgr

[ubfan1]

grubx64.efi uses grub.cfg just like the old grub to select which system to boot. The location /EFI/ubuntu/grub.cfg is different, but newer releases just have a three line stub for grub.cfg which brings in the "maintained" grub.cfg from /boot/grub/grub.cfg

[geohei]

You can only have one efi partition per drive. Not sure what happens with two?
2 EFI partitions are allowed by UEFI specifications.
See article 2 (from srs5694)
https://bbs.archlinux.org/viewtopic.php?id=168503

I do not know details of efibootmgr, but I would think you still have to install grub from Ubuntu. The boot manager is just adding a boot entry into the UEFI memory.
Yes, sure. This is not about grub. UEFI starts grubx64.efi (= bootloader), and then grub takes over.

Launch EFI Shell from File System Device
https://wiki.archlinux.org/index.php/Unified_Extensible_Firmware_Interface#UEFI_Shell
http://software.intel.com/en-us/articles/efi-shells-and-scripting/
http://linux.die.net/man/8/efibootmgr
All this is more or less known, but doesn't answer my question.
How does grubx64.efi (located in sda5) know that it should continue to boot in sda6 (which resides the Linux on an ext4 filesystem)?

grubx64.efi uses grub.cfg just like the old grub to select which system to boot. The location /EFI/ubuntu/grub.cfg is different, but newer releases just have a three line stub for grub.cfg which brings in the "maintained" grub.cfg from /boot/grub/grub.cfg
grubx64.efi is located in ESP.
grub.cfg is located in Ubuntu partition (/).
/EFI/ubuntu/grub.cfg doesn't exist on my system.
/boot/grub/grub.cfg exists on Ubuntu partition (/) and is required, but how does grubx64.efi know where to find this file since it has no knowledge about the lacation of the Ubuntu partition (/).

[oldfred]

thread closed. You started a new thread on similar related issues.

http://ubuntuforums.org/showthread.php?t=2169804