It's a bit difficult to find an easy to understand explanation of what
/boot/efi/ actually are.
I've found some possible answers through testing and googling but would be very happy if someone with experience could challenge or confirm my findings / way of thinking.
- Compatibility Support Module (CSM) in the motherboard is turned OFF
- Fast Boot and Secure Boot in the motherboard are both turned OFF
- Operating System is Ubuntu Server 22.04
- Setup uses two disks with identical capacity (for RAID 1)
- Both disks are in GPT format and on both disks the EFI-System Partition is partition number
/is a software RAID 1 created with
- More broadly: I'm doing some testing to better understand how software RAID works and how I can deal with possible RAID "errors" (e.g. swapping a faulty disk, booting from only one of the disks etc.) in the future.
My findings (based on the context above) / Questions
/boot is not the EFI-System Partition. I.e. it does not contain the bootloader.
However, it contains the GRUB configuration files (
/boot/grub/ in my case).
I tested this by installing the bootloader (with the ubuntu server installer) on both disks, then made a change to the grub configuration file (
intel_iommu=on as a "dummy" flag then ran
update-grub), shut down the server and physically removed the drive whose EFI partition was mounted when I did the change). Server booted but got stuck in ''emergency'' mode because the OS couldn't find the drive with the EFI-Partition that was specified in
/etc/fstab (the ubuntu server installer added the mount point with the UUID of the drive I removed).
cat /proc/cmdline did show that
intel_iommu=on was specified.
This leads me to believe that the grub configuration isn't stored on the EFI-Partition and is part of the software RAID I created when I installed the system.
/boot/efi is a mount point of the EFI-System Partition which in turn gives access to the installed bootloader.
At least one of the drives needs to have a bootloader installed (on the EFI-System Partition that is mounted here), otherwise the system will not boot.
Bootloader (GRUB) can be re-installed by running
3.) [If 1. and 2. are indeed true], question: Is it necessary for the Ubuntu OS to mount the EFI-System Partition in order to function?
Could I omit the mount instruction inside of
This is just a question out of curiosity.