加密分区中更新GRUB的方法及Ubuntu 16.04更新后GRUB故障求助

Hey there, let's tackle this GRUB problem you ran into after updating Ubuntu 16.04, plus cover how to update GRUB on encrypted partitions.

First: Get Back Into Your System From the GRUB Rescue Prompt #

Since you're stuck at the black GRUB screen with just a prompt, here's how to manually boot into Ubuntu temporarily:

1. First, identify your Ubuntu root partition by running:

   ls
   

   You'll see entries like (hd0,gpt1), (hd0,gpt2)—test which one is your root partition by running:

   ls (hd0,gpt2)/boot
   

   If you see kernel files (like vmlinuz-xxx-generic), that's your root partition.

2. Set the root partition in GRUB:

   set root=(hd0,gpt2)  # Replace with your actual partition
   

3. Load the kernel and initrd image (use TAB to auto-complete the kernel version):

   linux /boot/vmlinuz-<your-kernel-version>-generic root=/dev/sda2 ro  # sda2 matches the partition from step 1
   initrd /boot/initrd.img-<your-kernel-version>-generic
   

4. Boot into Ubuntu:

   boot
   

Once you're in the system, we can fix GRUB permanently.

Permanently Repair GRUB (Non-Encrypted Partitions) #

Run these commands to refresh and reinstall GRUB:

sudo update-grub
sudo grub-install /dev/sda  # Note: This is the disk (e.g., /dev/sda), not a partition like /dev/sda2

Reboot your system—you should now see the normal GRUB menu.

Updating GRUB on Encrypted Partitions #

If your Ubuntu root partition is encrypted, follow these steps to safely update GRUB:

1. Unlock the encrypted partition (replace /dev/sda2 with your encrypted partition, ubuntu-crypt is a temporary mapping name):

   sudo cryptsetup luksOpen /dev/sda2 ubuntu-crypt
   

2. Mount the root partition to /mnt:

   sudo mount /dev/mapper/ubuntu-crypt /mnt
   

3. Mount the /boot partition if you have a separate one (replace /dev/sda1 with your boot partition):

   sudo mount /dev/sda1 /mnt/boot
   

4. Bind critical system directories to access them from the chroot environment:

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

5. Enter the chroot environment to work within your installed system:

   sudo chroot /mnt
   

6. Update and reinstall GRUB:

   update-grub
   grub-install /dev/sda  # Again, target the disk, not a partition
   

7. Clean up and unmount:
   Exit the chroot, then unmount all the directories and close the encrypted partition:

   exit
   sudo umount /mnt/sys
   sudo umount /mnt/proc
   sudo umount /mnt/dev
   sudo umount /mnt/boot  # Skip this if you didn't mount a separate boot partition
   sudo umount /mnt
   sudo cryptsetup luksClose ubuntu-crypt
   

Reboot your system, and GRUB should be properly updated for your encrypted setup.

内容的提问来源于stack exchange，提问作者Jarodd