#!/usr/bin/env bash
#
# JbTecWiz Support Centre -- generated fix script
#
# Fault : grub rescue> -- "no such partition" or "unknown filesystem"
# Fix   : Reinstall GRUB from a live USB
# Source: https://jbtecwiz.com/support/lnx-grub-rescue
#
# Run as     : Live USB session
# Expect     : 45 minutes
# Risk       : medium
# Reversible : yes
#
# WHEN THIS IS THE RIGHT FIX
#   The rescue prompt route failed, or /boot itself is damaged.
#
# HOW TO UNDO IT
#   Reinstalling GRUB is repeatable and non-destructive to data.
#
# Walks the fix one step at a time and asks before each. Steps with no
# command are yours to do -- it prints those and waits. DRYRUN=1 prints
# without executing; UNATTENDED=1 does not ask.
#
# --------------------------------------------------------------------
# NO WARRANTY - USE AT YOUR OWN RISK
#
# This script is provided by JbTecWiz as-is and with no warranty of any
# kind, express or implied. You run it entirely at your own risk.
#
# JbTecWiz accepts no liability for any loss or damage arising from its
# use, including but not limited to data loss, downtime, or configuration
# changes that turn out to be wrong for your system.
#
# You are responsible for reading this script before running it, for
# satisfying yourself that it suits the machine in front of you, and for
# having a working backup first. Some steps cannot be undone.
# --------------------------------------------------------------------

set -uo pipefail
DRYRUN="${DRYRUN:-0}"
UNATTENDED="${UNATTENDED:-0}"
failed=0

rule() { printf "\n%s\n" "$(printf '-%.0s' $(seq 1 70))"; if [ $# -gt 0 ]; then echo "$1"; fi; }
prose() { echo "$1" | fold -s -w 74 | sed "s/^/  /"; }

# Returns 0 when the caller should run the command, 1 when it should not.
# A manual step always returns 1 -- there is nothing for the caller to run.
step() {  # step <n> <do> <why> <manual|cmd> [command lines...]
  local n="$1" dotext="$2" why="$3" mode="$4"; shift 4
  rule "  Step $n of 7"
  prose "$dotext"
  if [ -n "$why" ]; then echo; prose "$why"; fi
  if [ "$mode" = "manual" ]; then
    echo; echo "  -> Do this yourself, then press Enter to carry on."
    if [ "$UNATTENDED" = "0" ] && [ "$DRYRUN" = "0" ]; then read -r _; fi
    return 1
  fi
  echo; printf "    %s\n" "$@"; echo
  if [ "$DRYRUN" = "1" ]; then echo "  (dry run -- not executed)"; return 1; fi
  if [ "$UNATTENDED" = "0" ]; then
    read -r -p "  Run this step? [Y]es / [S]kip / [Q]uit " a
    case "$a" in
      [Qq]*) echo "  Stopped at your request."; exit 0 ;;
      [Ss]*) echo "  Skipped."; return 1 ;;
    esac
  fi
  return 0
}

rule
echo "  grub rescue> -- "no such partition" or "unknown filesystem""
echo "  Reinstall GRUB from a live USB"
echo
echo "  Risk: medium   Reversible   45 minutes"
echo
prose 'No warranty. Use at your own risk - JbTecWiz accepts no liability. Read it before you run it, and have a backup.'
rule
echo
if [ "$UNATTENDED" = "0" ] && [ "$DRYRUN" = "0" ]; then
  read -r -p "  Ready? [y/N] " go
  case "$go" in [Yy]*) ;; *) echo "  Nothing was changed."; exit 0;; esac
fi

if step 1 'Boot the live USB and identify the partitions.' '' cmd 'lsblk -f' 'sudo blkid'; then
  lsblk -f
  sudo blkid
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 1 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 2 'Mount the root filesystem, activating LVM first if used.' '' cmd 'sudo vgchange -ay' 'sudo mount /dev/sda2 /mnt'; then
  sudo vgchange -ay
  sudo mount /dev/sda2 /mnt
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 2 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 3 'Mount /boot and, on a UEFI machine, the EFI partition.' 'Only mount boot/efi if they are separate partitions -- check the fstab of the mounted root with `cat /mnt/etc/fstab` rather than assuming.' cmd 'sudo mount /dev/sda1 /mnt/boot' 'sudo mount /dev/sda1 /mnt/boot/efi'; then
  sudo mount /dev/sda1 /mnt/boot
  sudo mount /dev/sda1 /mnt/boot/efi
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 3 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 4 'Bind the virtual filesystems and enter the installation.' '' cmd 'for d in dev dev/pts proc sys run; do sudo mount --bind /$d /mnt/$d; done' 'sudo chroot /mnt /bin/bash'; then
  for d in dev dev/pts proc sys run; do sudo mount --bind /$d /mnt/$d; done
  sudo chroot /mnt /bin/bash
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 4 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 5 'Reinstall the bootloader. For BIOS/MBR, target the DISK not a partition.' '' cmd 'grub-install /dev/sda' 'update-grub'; then
  grub-install /dev/sda
  update-grub
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 5 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 6 'For UEFI, install to the EFI directory instead.' '' cmd 'grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntu' 'update-grub'; then
  grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntu
  update-grub
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 6 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 7 'Leave and unmount cleanly.' '' cmd 'exit' 'sudo umount -R /mnt' 'sudo reboot'; then
  exit
  sudo umount -R /mnt
  sudo reboot
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 7 failed. The rest of the fix may depend on it." >&2
  fi
fi

rule "  Confirm it worked"
prose 'The machine boots to the GRUB menu and into the system.'
if [ "$DRYRUN" = "0" ]; then
  sudo efibootmgr -v
fi

rule
if [ "$failed" -gt 0 ]; then
  echo "  Finished with $failed failed step(s)."
  echo "  Read the full write-up at https://jbtecwiz.com/support/lnx-grub-rescue"
else
  echo "  Finished."
fi
echo
prose 'To undo: Reinstalling GRUB is repeatable and non-destructive to data.'
rule