四系统启动Mid2014款15寸Retina MacBook Pro升级10.12的启动保护疑问

Hey, let's break down your question step by step—since you've got a custom 4-system boot setup on that 2014 15" Retina MBP, I totally get why you're cautious after the Windows 10 update disaster. Here's what you need to know:

1. 升级对启动项/分区的核心风险 #

• First off: macOS Sierra (10.12) won't actively modify non-macOS partitions during a standard upgrade, but the big risk is to your EFI partition (/dev/disk0s1). macOS upgrades have a habit of overwriting or resetting EFI boot priorities, and may even clean up third-party boot loaders (like your Debian GRUB) to set its own bootx64.efi as the default.
• Since you're booting Debian directly without rEFInd, your current setup relies on GRUB being registered as the top-priority boot loader in the EFI firmware. This is exactly the kind of configuration that macOS upgrades love to break.

2. Is dd backing up the EFI partition enough? #

• Short answer: Yes, but you need to do it right
  • Before upgrading, boot into single-user mode or an external drive (to avoid the EFI partition being locked), then run this command to back it up to an external storage device (don't save the backup on your internal drive—just in case):

    sudo dd if=/dev/disk0s1 of=/Volumes/YourExternalDrive/efi_backup.img bs=1m
    

  • After the upgrade finishes, if your boot setup is messed up (e.g., it boots straight to macOS instead of Debian), boot into macOS, mount your external drive, and run the reverse command to restore:

    sudo dd if=/Volumes/YourExternalDrive/efi_backup.img of=/dev/disk0s1 bs=1m
    

  • Reboot after restoring, and your original boot priority (Debian default) should be back.

3. Extra safeguards (optional but highly recommended) #

• Document your EFI structure first: Mount the EFI partition with sudo diskutil mount /dev/disk0s1, then run ls /Volumes/EFI to note where your Debian GRUB lives (usually EFI/debian/grubx64.efi). If the dd restore doesn't work for some reason, you can manually re-register GRUB via macOS's bless command or from a Debian live USB.
• Temporarily set macOS as default boot before upgrading: Use this command to make macOS the default boot loader before starting the upgrade—this reduces the chance of the installer getting confused and making unexpected changes to the EFI:

  sudo bless --mount / --setBoot
  

  You can switch back to Debian default after restoring the EFI backup.
• Have a Debian live USB ready: If worst comes to worst and the EFI partition gets corrupted beyond the dd restore, boot from a Debian live USB, mount your Debian root partition and the EFI partition, then re-install GRUB to EFI:

  sudo grub-install --target=x86_64-efi --efi-directory=/mnt/efi --bootloader-id=debian --recheck
  

4. Partition safety note #

• macOS Sierra won't resize or delete your existing non-macOS partitions as long as your macOS partition has enough free space (aim for at least 10GB). Still, it's a good idea to run diskutil list before upgrading to confirm all partitions are recognized and error-free.

内容的提问来源于stack exchange，提问作者nate