#!/usr/bin/env bash
#
# JbTecWiz Support Centre -- generated fix script
#
# Fault : grub rescue> -- "no such partition" or "unknown filesystem"
# Fix   : Boot once from the rescue prompt
# Source: https://jbtecwiz.com/support/lnx-grub-rescue
#
# Run as     : grub rescue> prompt
# Expect     : 20 minutes
# Risk       : low
# Reversible : yes
#
# WHEN THIS IS THE RIGHT FIX
#   No live media to hand. This gets you booted once; it does not repair
#   anything permanently.
#
# HOW TO UNDO IT
#   None -- nothing on disk is changed until the grub-install step.
#
# 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 $n of 6"
  prose "$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 "  Boot once from the rescue prompt"
echo
echo "  Risk: low   Reversible   20 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 'List the partitions GRUB can see.' 'It prints things like (hd0) (hd0,gpt1) (hd0,gpt2). These are GRUB'\''s names, not Linux'\''s -- gpt2 here is roughly /dev/sda2.' cmd 'ls'; then
  ls
  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 'Find which one holds /boot/grub by inspecting each in turn.' '' cmd 'ls (hd0,gpt2)/boot/grub'; then
  ls (hd0,gpt2)/boot/grub
  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 'Point GRUB at it and load the modules.' '' cmd 'set prefix=(hd0,gpt2)/boot/grub' 'set root=(hd0,gpt2)' 'insmod normal' 'normal'; then
  set prefix=(hd0,gpt2)/boot/grub
  set root=(hd0,gpt2)
  insmod normal
  normal
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 3 failed. The rest of the fix may depend on it." >&2
  fi
fi

step 4 'The full menu should appear. Boot the system normally.' '' manual || true

if step 5 'Once booted, make it permanent -- otherwise the next restart lands right back here.' 'Do not skip this. Everything above lives only in memory.' cmd 'sudo grub-install /dev/sda' 'sudo update-grub'; then
  sudo grub-install /dev/sda
  sudo 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 'On RHEL-family use the other tool name.' '' cmd 'sudo grub2-install /dev/sda' 'sudo grub2-mkconfig -o /boot/grub2/grub.cfg'; then
  sudo grub2-install /dev/sda
  sudo grub2-mkconfig -o /boot/grub2/grub.cfg
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 6 failed. The rest of the fix may depend on it." >&2
  fi
fi

rule "  Confirm it worked"
prose 'The machine restarts into the normal GRUB menu.'
if [ "$DRYRUN" = "0" ]; then
  sudo grub-install --version && lsblk -f
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: None -- nothing on disk is changed until the grub-install step.'
rule