Fabrice Quenneville
822bcf70eb
Covers chroot setup from a live environment, GRUB reinstall, and kernel recovery for when boot fails but the root filesystem is intact.
153 lines
3.2 KiB
Markdown
153 lines
3.2 KiB
Markdown
# EFI Partition Repair
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## Table of Contents
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- [EFI Partition Repair](#efi-partition-repair)
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- [Table of Contents](#table-of-contents)
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- [Overview](#overview)
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- [Placeholders](#placeholders)
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- [Repair Procedure](#repair-procedure)
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- [1. Verify What You're Working With](#1-verify-what-youre-working-with)
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- [2. Mount Everything for Chroot](#2-mount-everything-for-chroot)
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- [3. Chroot In](#3-chroot-in)
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- [4. Reinstall GRUB](#4-reinstall-grub)
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- [5. Regenerate GRUB Config](#5-regenerate-grub-config)
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- [6. Verify fstab](#6-verify-fstab)
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- [7. Exit and Reboot](#7-exit-and-reboot)
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## Overview
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Use this procedure when a Debian machine fails to boot but the root filesystem appears intact — for example after a failed kernel upgrade, a corrupted EFI partition, or GRUB being wiped by another OS. Boot from a live environment, chroot into the installed system, and reinstall GRUB.
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## Placeholders
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Replace the placeholders below with the appropriate values for your setup:
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- **Devices**
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- Disk: `<disk>` (e.g., /dev/sda, /dev/nvme0n1)
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- EFI partition: `<efi-part>` (e.g., /dev/sda1, /dev/nvme0n1p1)
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- Root partition: `<root-part>` (e.g., /dev/sda2, /dev/nvme0n1p2)
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- **Filesystem**
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- Root subvolume name: `<root-subvol>` (e.g., @rootfs)
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## Repair Procedure
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### 1. Verify What You're Working With
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Identify the disk layout, partition types, UUIDs, and current mount points:
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```bash
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lsblk -o NAME,SIZE,FSTYPE,PARTTYPE,UUID,MOUNTPOINT
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```
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Confirm which partition is EFI and which is root before proceeding.
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### 2. Mount Everything for Chroot
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**Mount the root filesystem**
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```bash
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mkdir -p /mnt
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mount -o subvol=<root-subvol> <root-part> /mnt
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```
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**Mount the EFI partition**
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```bash
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mkdir -p /mnt/boot/efi
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mount <efi-part> /mnt/boot/efi
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```
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**Bind mount the pseudo-filesystems**
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```bash
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mkdir -p /mnt/{dev,proc,sys,run}
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mount --bind /dev /mnt/dev
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mount --bind /proc /mnt/proc
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mount --bind /sys /mnt/sys
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mount --bind /run /mnt/run
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```
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**Bind mount EFI vars**
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Required for `grub-install` to write boot entries to the firmware:
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```bash
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mount --bind /sys/firmware/efi/efivars /mnt/sys/firmware/efi/efivars
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```
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### 3. Chroot In
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```bash
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chroot /mnt /bin/bash
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source /etc/profile
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export PS1="(chroot) $PS1"
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```
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### 4. Reinstall GRUB
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**Run grub-install on the disk**
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```bash
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grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=debian --recheck <disk>
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```
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If you get an error about EFI vars not being writable:
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```bash
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mount -o remount,rw /sys/firmware/efi/efivars
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```
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Then re-run `grub-install`.
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### 5. Regenerate GRUB Config
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```bash
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update-grub
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```
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Check the output — it should find your kernel on the btrfs volume. If it complains about not finding a kernel, you may need to also reinstall it:
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**Check what kernel is installed**
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```bash
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dpkg -l | grep linux-image
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```
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**Reinstall the kernel if missing or broken**
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```bash
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apt-get install --reinstall linux-image-amd64
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```
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Then re-run `update-grub`.
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### 6. Verify fstab
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Confirm the EFI and root entries look correct before rebooting:
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```bash
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cat /etc/fstab
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```
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### 7. Exit and Reboot
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**Exit the chroot**
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```bash
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exit
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```
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**Unmount everything**
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```bash
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umount -R /mnt
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```
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**Reboot**
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```bash
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reboot
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```
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