#!/usr/bin/env bash
#
# JbTecWiz Support Centre -- generated fix script
#
# Fault : MySQL: "Too many connections" or "Access denied for user"
# Fix   : Point the client at the right socket
# Source: https://jbtecwiz.com/support/lnx-web-mysql-connections
#
# Run as     : Root shell
# Expect     : 20 minutes
# Risk       : low
# Reversible : yes
#
# WHEN THIS IS THE RIGHT FIX
#   Error 2002, cannot connect to local server through socket.
#
# HOW TO UNDO IT
#   Remove the client configuration file to return to the default.
#
# 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

if [ "$(id -u)" -ne 0 ]; then
  echo "  This fix is documented as needing root. Re-run with sudo." >&2
  exit 3
fi

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 $n of 5"
  prose "$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 "  MySQL: "Too many connections" or "Access denied for user""
echo "  Point the client at the right socket"
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 'Confirm the server is actually running first.' '' cmd 'systemctl status mysql mariadb --no-pager 2>/dev/null | head -20' 'sudo ss -tlnp | grep 3306'; then
  systemctl status mysql mariadb --no-pager 2>/dev/null | head -20
  sudo ss -tlnp | grep 3306
  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 where the socket really is.' 'The client has a compiled-in default that frequently differs from where the packaged server puts it. That mismatch is this whole error, and it looks exactly like a stopped service.' cmd 'sudo mysqladmin variables 2>/dev/null | grep -w socket' 'ls -l /var/run/mysqld/ /run/mysqld/ /tmp/mysql.sock 2>/dev/null'; then
  sudo mysqladmin variables 2>/dev/null | grep -w socket
  ls -l /var/run/mysqld/ /run/mysqld/ /tmp/mysql.sock 2>/dev/null
  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 the client at it in the configuration rather than passing --socket every time.' '' cmd 'printf '\''[client]\nsocket = /var/run/mysqld/mysqld.sock\n'\'' | sudo tee /etc/mysql/conf.d/client-socket.cnf'; then
  printf '[client]\nsocket = /var/run/mysqld/mysqld.sock\n' | sudo tee /etc/mysql/conf.d/client-socket.cnf
  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 'If the server will not start, read why.' '' cmd 'sudo journalctl -u mysql -n 50 --no-pager' 'sudo tail -50 /var/log/mysql/error.log'; then
  sudo journalctl -u mysql -n 50 --no-pager
  sudo tail -50 /var/log/mysql/error.log
  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 'A full disk is a common reason a database refuses to start with a misleading error.' '' cmd 'df -h /var/lib/mysql'; then
  df -h /var/lib/mysql
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 5 failed. The rest of the fix may depend on it." >&2
  fi
fi

rule "  Confirm it worked"
prose 'mysql connects with no explicit socket argument.'
if [ "$DRYRUN" = "0" ]; then
  mysql -e 'SELECT VERSION()'
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-web-mysql-connections"
else
  echo "  Finished."
fi
echo
prose 'To undo: Remove the client configuration file to return to the default.'
rule