物理Ubuntu机器转VirtualBox镜像后启动报错：No bootable Medium found!

Hey there, sorry you're stuck on this boot error—let's break down the problem and fix it step by step!

问题根源 #

The key issue here is that you used dd to back up only a single partition (/dev/sda1) instead of the entire physical disk (/dev/sda). Bootable systems rely on the master boot record (MBR) or GRUB bootloader, which lives in the very first sector of the whole disk (not inside a single partition like /dev/sda1). Your converted VMDK only has the data from /dev/sda1—it's missing the critical boot metadata VirtualBox needs to start the system.

解决方法 #

方法1：重新制作完整镜像（最稳妥）

This is the recommended approach because it captures all the necessary boot and partition data:

• Go back to your physical Ubuntu machine, and run this command to back up the entire disk (not just /dev/sda1):

  dd if=/dev/sda of=/mnt/f/disk.raw bs=1024
  

  Note: This will include all partitions (like swap, data partitions) and the boot sector, so your VirtualBox VM will have an exact copy of the physical system.
• Convert the full raw image to VMDK again:

  VBoxManage convertfromraw /mnt/f/disk.raw /mnt/f/disk.vmdk --format VMDK
  

• Create a new VirtualBox VM (or replace the existing disk in your current VM) with this new VMDK, then try booting again.

方法2：修复现有镜像的引导（如果不想重新备份）

If re-backing up the disk isn't feasible right now, you can repair the bootloader on your existing VMDK:

1. In VirtualBox, edit your VM's settings: add an Ubuntu installation ISO as a CD/DVD drive, and set the VM to boot from the CD first.
2. Start the VM and select "Try Ubuntu" (don't install it).
3. Open a terminal and identify your VMDK's partition:

   lsblk
   

   Look for a partition that matches the size of your original /dev/sda1 (it'll probably be /dev/sda1 in the live environment).
4. Mount the partition and fix GRUB:

   sudo mount /dev/sda1 /mnt
   sudo mount --bind /dev /mnt/dev
   sudo mount --bind /proc /mnt/proc
   sudo mount --bind /sys /mnt/sys
   sudo chroot /mnt
   grub-install /dev/sda
   update-grub
   exit
   

5. Unmount the mounted directories:

   sudo umount /mnt/sys
   sudo umount /mnt/proc
   sudo umount /mnt/dev
   sudo umount /mnt
   

6. Shut down the VM, remove the Ubuntu ISO from the CD drive, set the VM to boot from the hard disk first, then try starting it again.

额外检查 #

• Double-check your VM's System > Boot Order settings to ensure the hard disk is at the top of the list.
• Confirm that your VM's architecture (64-bit) matches your physical Ubuntu system—if your physical machine is 32-bit, selecting "Ubuntu 64-bit" would cause issues (but it sounds like you got this right!).

备注：内容来源于stack exchange，提问作者user7864052