#! /bin/sh -e

# Simple script to maybe reboot the machine.

#  We want to reboot if:
#
# * There's a new kernel installed.
#
#  ...also if we are running from cron, we probably only want to reboot if
# there's nobody logged into the machine (Eg. the *-test.* machines, or
# maybe someone debugging a staging machine).

CUR_KERNEL="$(uname -r)"

_DEF_KERN_PATH="$(grubby --default-kernel)"
NXT_KERNEL=$(basename "$_DEF_KERN_PATH" | sed 's/^vmlinuz-//')

# How many users are logged into the machine.
USER_COUNT=$(who | wc -l)


function err {
  echo "$@" >&2
}

function maybe_reboot {
  if [ "x$CUR_KERNEL" != "x$NXT_KERNEL" ]; then
    reboot
  fi
}


case "$1" in
  info)
    echo "-------- Kernel Status Check --------"
    echo "Running: $CUR_KERNEL"
    if [ "x$CUR_KERNEL" != "x$NXT_KERNEL" ]; then
    echo "   Next: $NXT_KERNEL"
    fi
    echo "-------------------------------------"
    echo "Users: $USER_COUNT"
    ;;

  maybe-reboot)
    maybe_reboot
    ;;

  maybe-cron-reboot|cron-maybe-reboot)
    if [ "$USER_COUNT" -eq 0 ]; then
      maybe_reboot
    fi
    ;;

  *)
    err "Usage: $0 info | maybe-reboot | cron-maybe-reboot"
    exit 1
esac