Restored Linux virtual machine fails to boot

I. Prerequisites

• You must have a Linux LiveCD matching the distribution and release version of the restored Linux system that is compatible with target system hardware. It can be either a distribution-supplied live/rescue CD or Custom Veeam Recovery Media generated on the machine prior to restore.
• You must be aware of the disk and volume layout of the target system and the devices corresponding to the root filesystem and boot partitions. If this information is not readily available, you may use File-level Restore (with Veeam Recovery Media, Veeam Agent for Linux, or Veeam Backup&Replication) to mount the backup contents and inspect the /etc/fstab file.

II. Preparation

1. Boot from the LiveCD or Custom Veeam Recovery Media.
2. Switch to the bash shell and elevate to root user if necessary.
3. Locate the volumes/partitions hosting the root and boot filesystems. You can use commands like lsblk (list hierarchy of block devices), lvdisplay (list logical volumes), etc.

III. Mounting

1. Create a directory where the system root will be mounted.

Example:

2. Mount the device hosting the root filesystem inside the directory (/targetroot).

Example for sda3 partition:

3. Mount the boot partition inside /targetroot/boot.

Example for sda2 boot partition:

4. If UEFI is in use: The EFI system partition (/boot/efi) needs to be mounted to /targetroot/boot/efi.

Assuming EFI system partition on sda1:

5. Bind mount the pseudo filesystems inside target root - /dev, /proc, /sys, and /run:

6. Chroot into the mounted system:

IV. Rebuilding initramfs

Identifying and Correlating Kernel Versions to Initial Ramdisk Images

The initial ramdisk image (initramfs/initrd) is an image of an initial root filesystem used as a part of the Linux boot process. Initial ramdisk images are stored as files under /boot, named initramfs-<kernel version>.img or initrd-<kernel version>.

Example for Red Hat Enterprise Linux 8:

Initial ramdisk image files correspond to GRUB/GRUB2 boot menu entries - when a specific entry is selected in the boot menu, a corresponding initramfs image is loaded. The relation between GRUB menu entries and initial ramdisk image files can be determined via grub.cfg file (generally located under /boot/grub or /boot/grub2) - look for menuentry records which denote GRUB boot menu entries.

Example from SUSE Linux Enterprise Server 15 SP1:

### BEGIN /etc/grub.d/10_linux ###
menuentry 'SLES 15-SP1'  --class sles --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-bf547c2f-3d66-4be6-98c3-8efe845a940d' {
<...>
        echo    'Loading Linux 4.12.14-197.15-default ...'
        linuxefi /boot/vmlinuz-4.12.14-197.15-default root=UUID=bf547c2f-3d66-4be6-98c3-8efe845a940d  ${extra_cmdline} splash=silent resume=/dev/disk/by-path/pci-0000:03:00.0-scsi-0:0:0:0-part3 mitigations=auto quiet crashkernel=175M,high
        echo    'Loading initial ramdisk ...'
       initrdefi /boot/initrd-4.12.14-197.15-default
}

Finalizing

With the initramfs having been rebuilt, exit the chroot environment: