UEFI fails to detect boot disk

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Environment

SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server 15

Situation

UEFI system is not able to detect boot disk. However, using SLES DVD "Boot Linux System" detect existing installed SLES OS and boot it from hard disk successfully.

The disk with the /boot/efi device shows:

efi12sp3:~ # parted -s /dev/vda print
...
Partition Table: gpt
Disk Flags: pmbr_boot
...

Resolution

To fix this problem:

Check the boot disk is not corrupted
Remove pmbr_boot label in case it is set

To check second point boot from SLES DVD and select “Rescue Mode”. Use parted command remove the pmbr_boot disk flag.

1. Identify the boot device with mount point /boot/efi

efi12sp3:~ # lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sr0     11:0    1  3.6G  0 rom  
vda    253:0    0   20G  0 disk 
├─vda1 253:1    0  156M  0 part /boot/efi  <==================
├─vda2 253:2    0  1.5G  0 part [SWAP]
└─vda3 253:3    0 18.4G  0 part /var/lib/mysql

2. Print the partition table

efi12sp3:~ # parted -s /dev/vda print
Model: Virtio Block Device (virtblk)
Disk /dev/vda: 21.5GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: pmbr_boot <================================

Number  Start   End     Size    File system     Name     Flags
 1      1049kB  165MB   164MB   fat16           primary  boot
 2      165MB   1727MB  1562MB  linux-swap(v1)  primary
 3      1727MB  21.5GB  19.7GB  btrfs           primary

3. Remove the pmbr_boot disk flag.

efi12sp3:~ # parted -s /dev/vda disk_set pmbr_boot off

4. Confirm the pmbr_boot disk flag has been removed.

efi12sp3:~ # parted -s /dev/vda print
Model: Virtio Block Device (virtblk)
Disk /dev/vda: 21.5GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:           <================================

Number  Start   End     Size    File system     Name     Flags
 1      1049kB  165MB   164MB   fat16           primary  boot
 2      165MB   1727MB  1562MB  linux-swap(v1)  primary
 3      1727MB  21.5GB  19.7GB  btrfs           primary

5. Reboot to test.

Cause

One cause includes having the pmbr_boot disk flag set. It enables the boot flag on the GPT’s protective MBR partition. The pmbr_boot flag is needed for old BIOS computers to boot from GPT disks.

Additional Information

Some servers support both Legacy boot and UEFI boot. In case OS installation was done in Legacy mode, pmbr_boot is set on. In case OS installation was done in UEFI mode, pmbr_boot is set off. If the disk was moved from server to server where old server is Legacy boot and new server UEFI ; the server will not be able to boot from hard disk.

Using old YaST bootloader to switch between GRUB2 and GRUB2 for EFI might cause such issue where YaST doesn’t remove pmbr_boot flags ; make sure yast2-bootloader-3.3.1-3.3.1 and newer is being used.

In a GPT, the first sector of the disk is reserved for a "protective MBR" such that booting a BIOS-based computer from a GPT disk is supported, but the boot loader and O/S must both be GPT-aware.

Disclaimer

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