Restoring the OS bootloader

If your BareMetal legacy BIOS server experiences GRUB bootloader issues, you can use the Rescue CD to restore it. Proceed with the following steps in the KVM console.

To restore the bootloader:

1. Start the server from the Rescue CD image.

   In the main SystemRescue menu, select Boot SystemRescue using default options, press ENTER and wait for SystemRescue to load.

2. List server disks and their partitions:

   fdisk -l
   

   Result:

   Disk /dev/sda: 838.36 GiB, 900185481216 bytes, 1758174768 sectors
   Disk model: SAMSUNG MZ7GE900
   Units: sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/0 size (minimum/optimal): 512 bytes / 512 bytes
   Disklabel type: gpt
   Disk identifier: D79F5407-DEEC-4A1D-983F-3AC5********
   
   Device      Start      End         Sectors      Size  Type
   /dev/sda1   2048       614399      612352       299M  BIOS boot
   /dev/sda2   614400     21585919    20971520     10G   Linux filesystem
   /dev/sda3   21585920   34168831    12582912     6G    Linux filesystem
   /dev/sda4   34168832   1732861951  1698693120   810G  Linux filesystem
   
   
   Disk /dev/sdb: 838.36 GiB, 900185481216 bytes, 1758174768 sectors
   Disk model: SAMSUNG MZ7GE900
   Units: sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/0 size (minimum/optimal): 512 bytes / 512 bytes
   Disklabel type: gpt
   Disk identifier: CDZACB4C-1618-4BAF-A6BB-D2B9********
   
   Device      Start      End         Sectors      Size  Type
   /dev/sdb1   2048       614399      612352       299M  BIOS boot
   /dev/sdb2   614400     21585919    20971520     10G   Linux filesystem
   /dev/sdb3   21585920   34168831    12582912     6G    Linux filesystem
   /dev/sdb4   34168832   1732861951  1698693120   810G  Linux filesystem
   
   Disk /dev/md127: 6 GiB, 6438256640 bytes, 12574720 sectors
   Units: sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/0 size (minimum/optimal): 512 bytes / 512 bytes
   
   Disk /dev/md126: 9.99 GiB, 10729029632 bytes, 20955136 sectors = 512 bytes
   Units: sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/0 size (minimum/optimal): 512 bytes / 512 bytes
   
   Disk /dev/md125: 809.88 GiB, 869596659712 bytes, 1698430976 sectors
   Units: sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/0 size (minimum/optimal): 512 bytes / 512 bytes
   
   Disk /dev/loop: 824.97 MiB, 865046528 bytes, 1689544 sectors
   Units: sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/O size (minimum/optimal): 512 bytes / 512 bytes
   

   In the example above, the fdisk utility displayed information about the /dev/sda and /dev/sdb physical disks, their partitions, and the partitions of the server’s RAID array: /dev/md127, /dev/md126, and /dev/md125.

   The reference server uses the following partition scheme:

   • /dev/md126: /boot partition.
   • /dev/md127: SWAP partition.
   • /dev/md125: / root partition.

   You need to mount the /boot and / partitions in SystemRescue.

3. Mount BareMetal server’s root and boot partitions in SystemRescue:

   mount /dev/md125 /mnt/
   mount /dev/md126 /mnt/boot
   

   Note

   If the system has no RAID array, you need to mount physical disk partitions, e.g., /dev/sda1, /dev/sda2, directly.

   If you installed your OS using LVM, you need to mount the /dev/mapper partition.

   When using an UEFI bootloader, also mount the corresponding EFI system partition, e.g., mount /dev/sda3 /mnt/boot/efi, where /dev/sda3 is the EFI partition.

4. Mount the /sys, /proc, and /dev directories:

   mount --bind /sys /mnt/sys
   mount --bind /proc /mnt/proc
   mount --bind /dev /mnt/dev
   

5. Create a new SystemRescue shell environment using the server OS’s previously mounted BareMetal filesystem:

   chroot /mnt /bin/bash
   

6. If GRUB is not installed, install it on all disks you are planning to use as OS boot drives. If GRUB is already installed, proceed to the next step.

   In our example, you need to install GRUB on the /dev/sda and /dev/sdb disks.

   grub-install /dev/sda
   grub-install /dev/sdb
   

   Result:

   Installing for i386-pc platform.
   Installation finished. No error reported.
   

7. Generate a GRUB configuration file:

   update-grub
   

   Result:

   Sourcing file '/etc/default/grub'
   Sourcing file '/etc/default/grub.d/init-select.cfg'
   Generating grub configuration file ...
   Found linux image: /boot/uml inuz-5.15.0-130-generic
   Found initrd image: /boot/initrd.img-5.15.0-130-generic
   Found linux image: /boot/vmlinuz-5.15.0-113-generic
   Found initrd image: /boot/initrd.img-5.15.0-113-generic
   Found linux image: /boot/vmlinuz-5.15.0-25-generic
   Found initrd image: /boot/initrd.img-5.15.0-25-generic
   Warning: os-prober will not be executed to detect other bootable partitions.
   Systems on them will not be added to the GRUB boot configuration.
   Check GRUB_DISABLE_OS_PROBER documentation entry.
   done
   

8. Exit the chroot environment:

   exit
   

9. Disable the virtual CD drive in the KVM console:

   1. Click the CD icon or select Media → Virtual Media Wizard... in the top menu of the KVM console window.
   2. In the window that opens, click Disconnect under CD/DVD Media1.
   3. Click Close.

10. Restart the server:

    reboot
    

See alsoSee also

• Using the Rescue CD diagnostics and recovery tools
• Resetting the server root password
• Adding a new SSH key for a user
• Replacing a disk in a RAID array