CentOS 7 grub virtio error migrating to KVM

When migrating CentOS7 from physical servers or vmware / hyperv, it typically does not have virtio drivers built into it. This will often give grub or initramfs errors.

Once the image has been migrated, you have three choices:

1. Boot using Rescue mode from a latest CentOS or RockyOS (v8+), and choose to mount the existing machine (option 1). Version 8+ has the virtio drivers built in, so will see the drive no problem.
2. Boot using recovery mode. This is usually a grub menu option. We find this typically has virtio built in
3. Change emulation for the drive to IDE and boot as normal

Once booted into the os (or mounted via rescue cd and chroot /mnt/sysimage), change to root user if you aren’t already.

Run the following command to rebuild the initramfs:

mkinitrd -f --allow-missing --with=virtio_blk --preload=virtio_blk --with=virtio_net --preload=virtio_net --with=virtio_console --preload=virtio_console /boot/initramfs-$(uname -r).img $(uname -r)

Then just shut down the VM and boot it back up. new initramfs will now have the virtio drivers and be able to see the disk.