无法启动、GRUB不可用，请求修复EFI+LVM环境下的Ubuntu启动故障

Alright, let's break this down step by step—you’ve already got critical tools at your disposal (working Live USB, filesystem access, BIOS/boot menu functionality), so we can focus on restoring GRUB and getting your system back up.

First: Mount Your LVM System from the Live USB #

Since your setup uses LVM, we need to activate and mount your logical volumes before we can repair GRUB:

• Open a terminal in the Live USB environment.
• List all available logical volumes to identify your root partition:

  lvscan
  

  You’ll see output like ACTIVE '/dev/ubuntu-vg/root' [90.00 GiB] inherit—note that root volume path.
• Activate the volume group:

  vgchange -ay
  

• Mount your root partition to /mnt:

  mount /dev/ubuntu-vg/root /mnt
  

• Bind the system directories needed for chroot:

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

Second: Reinstall GRUB (BIOS/MBR or UEFI) #

The core issue is likely that GRUB is either corrupted on your boot disk or wasn’t properly registered in the BIOS/UEFI. Choose the method matching your system’s boot mode:

For BIOS/MBR Systems #

• Enter the chroot environment to work on your installed system:

  chroot /mnt
  

• Install GRUB directly to your primary hard drive (usually /dev/sda—double-check with fdisk -l if unsure):

  grub-install /dev/sda
  

• Update the GRUB configuration to detect all installed OSes:

  update-grub
  

For UEFI Systems #

• First, locate your EFI system partition (ESP) using fdisk -l—look for a small partition (100-500MB) labeled EFI System (usually /dev/sda1).
• Mount the ESP to /mnt/boot/efi:

  mount /dev/sda1 /mnt/boot/efi
  

• Enter chroot:

  chroot /mnt
  

• Install GRUB to the EFI partition:

  grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntu
  

• Update GRUB configuration:

  update-grub
  

Third: Verify Boot Order & GRUB Visibility #

• Reboot and enter your BIOS setup. Ensure your primary hard drive is set as the first boot device (above USB drives or other peripherals).
• If you still don’t see the GRUB menu after repair, adjust the GRUB settings to force the menu to show:
  1. Boot back into the Live USB, chroot into your system, and edit the GRUB config file:

     nano /etc/default/grub
     

  2. Change GRUB_TIMEOUT_STYLE=hidden to GRUB_TIMEOUT_STYLE=menu
  3. Set GRUB_TIMEOUT=10 (or another value to give you time to select options)
  4. Save and exit, then run update-grub again before rebooting.

Quick Checks to Rule Out Other Issues #

• Confirm your hard drive is detected in the BIOS—if it’s not showing up, you might have a hardware issue (but since you can access the filesystem via Live USB, this is unlikely).
• If you tried booting from another GRUB media and it couldn’t detect your drive, double-check that the other media supports LVM (most modern Live USBs do, but it’s worth confirming).

内容的提问来源于stack exchange，提问作者Asqiir