[SOLVED] Questions on using UEFI for RHEL VMS instead of BIOS questions

JockVSJock · 11-03-2016, 08:28 AM

Getting ready to move away from RHEL5 and to RHEL6 and I want to take advantage of tools like gdisk Vs fdisk, and I believe if I were to enable UEFI when building out the new RHEL6 servers will allow me to do this, correct?

I've noticed when that I'very enabled UEFI for the RHEL6 VMS, that there is a partitons that appears when building out, called /boot/efi. Typically when building and using BIOS, and creating a /boot partitons, I never placed this under LVM, would this still be the same, or can we put /boot/efi under LVM?

Also, Im wondering if anyone has had issues where they might have a RHEL VM that was created with BIOS or maybe with UEFI and then they had to swing disks to the opposite boot loader and if there were any issues?

The reason I'm asking is that I Google around and wasn't able to find any exact info on this topic, or I wasn't searching with the correct terms.

michaelk · 11-03-2016, 10:32 AM

Since RH6 uses legacy grub /boot still needs to be on its own partition.

jefro · 11-03-2016, 04:38 PM

Maybe grab a Centos iso and boot to a uefi vm client as see? I get the feeling that it should allow you to have all normal folders under lvm. Not sure why I think that either. michaelk is usually right however.

syg00 · 11-03-2016, 05:39 PM

/boot/efi needs to be findable by the EFI firmware. Well before your initrd has a chance to build LVM awareness.
Sorta like asking if you can put the MBR under LVM ...

jefro · 11-03-2016, 09:07 PM

Thought I read some round about way to do it. Guess not.

JockVSJock · 11-04-2016, 03:56 PM

Just noticed that I created /boot/efi not under LVM, I keep getting a "Bootable partitions cannot be on a logical volume" error.

This is a RHEL6 VM in vCenter.

So do I still need a /boot as well in addition to /boot/efi too, in order to make this work?

For the heck of it, I gave it /boot as well as /boot/efi and I was able to move forward with the RHEL6 install, however this seems odd to me.

JockVSJock · 11-05-2016, 07:16 AM

Wanted to pass this on to others, response from a RHEL forum:

Quote:

Yes, you still need a (ext2/3/4) /boot partition and a FAT /boot/efi ESP.

Have a look at: RHEL6 - Installation Guide - ⁠E.2.2. GRUB and the Boot Process on UEFI-based x86 Systems

Notice the EFI binary run is actually the GRUB bootloader, so the firmware reads grub.efi from the ESP, then GRUB loads and reads its bootloader entries from /boot and then we boot into the kernel (or memtest or an ISO or whatever other options you have in GRUB). That's why you need both.

It is also possible to launch directly into Linux kernel from the EFI firmware by running the kernel as an EFI executable, but this requires EFISTUB which was added in kernel 3.3. Reading https://wiki.archlinux.org/index.php/EFISTUB that implies you only need the ESP containing the kernel and the initramfs, not the bootloader partition.

I haven't setup EFI boot on RHEL7, but from RHEL7 - Installation Guide - ⁠6.14. Installation Destination it doesn't look like we've used EFISTUB, we still boot into GRUB and let it load the kernel, so you'd still need both /boot and /boot/efi there too.

jpollard · 11-06-2016, 08:33 AM

Quote:

Originally Posted by JockVSJock

Just noticed that I created /boot/efi not under LVM, I keep getting a "Bootable partitions cannot be on a logical volume" error.

That sounds like an improper partition table. EFI uses GPT partitions instead, no need for logical partitions.
I believe the bootable partition needs to be the first one, but not certain. It does have to contain a FAT filesystem though (otherwise the UFI prom can't read it).

Quote:

This is a RHEL6 VM in vCenter.

So do I still need a /boot as well in addition to /boot/efi too, in order to make this work?

Not necessarily, but it can help. As I understand it the efi partition is mounted as /boot/efi. The efi partition is only used to start grub2. After that, the kernel can be loaded from almost anything, but by convention it is in a filesystem mounted as /boot. The only advantage this has is keeping the kernel information segregated from the rest of the system. It CAN be part of the root filesystem as a directory /boot and still work.

Quote:

For the heck of it, I gave it /boot as well as /boot/efi and I was able to move forward with the RHEL6 install, however this seems odd to me.

It isn't wrong, just a choice. The difference is what is using the partition first. the efi partition is used by the system PROM/ROM UFI code to load grub. Grub2 can use just about any linux native filesystem, including LVM volumes.

tofino_surfer · 11-06-2016, 08:29 PM

Just noticed that I created /boot/efi not under LVM, I keep getting a "Bootable partitions cannot be on a logical volume" error.

>>>"That sounds like an improper partition table. EFI uses GPT partitions instead, no need for logical partitions."

You appear to be confused here pollard. No one is referring at all to MBR/DOS "logical partitions". They are referring to LVM virtual partitions which are termed a "logical volume".

jpollard · 11-07-2016, 04:09 AM

Quote:

Originally Posted by tofino_surfer

Just noticed that I created /boot/efi not under LVM, I keep getting a "Bootable partitions cannot be on a logical volume" error.

>>>"That sounds like an improper partition table. EFI uses GPT partitions instead, no need for logical partitions."

You appear to be confused here pollard. No one is referring at all to MBR/DOS "logical partitions". They are referring to LVM virtual partitions which are termed a "logical volume".

I still think it is invalid for use with efi.