#!/bin/bash
#
# kernelkeeper.sh
#
# Remove old kernels, keeping only the running kernel and the latest kernel
#
PID=$$

# root check
if [ "$UID" != "0" ]
then
  echo "You must run this script as root."
  exit 1
fi

# make sure it's ubuntu first
UBUNTU="`which lsb_release > /dev/null && lsb_release -a 2>/dev/null | grep Ubuntu`"
if [ "$UBUNTU" == "" ]
then
  echo "This script only works on Ubuntu and Ubuntu variants."
  exit 1
fi

# store list of metapackages currently installed
dpkg -l | grep \ linux | grep ii | awk '{print $2}' | grep -v [0-9] > /tmp/$PID.packagelist

# get current version
CURRENT="`uname -r | cut -d- -f1,2`"
REMOVE=""
echo "Current: $CURRENT"

# scan for kernels
for kernel in /boot/vmlinuz-*
do
  VERSION="`echo $kernel | cut -d- -f2,3`"
  VARIANT="`echo $kernel | cut -d- -f4`"
  # figure out what the latest version is
  LATEST="`find /boot -name 'vmlinuz-*' | grep $VARIANT | cut -d- -f2,3 | sort -V | tail -n1`"
  # if we're not using it and it's not new, plan to remove it
  if [ "$VERSION" != "$CURRENT" ] && [ "$VERSION" != "$LATEST" ]
  then
    REMOVE="$REMOVE linux-image-$VERSION-$VARIANT"
  fi
done

# remove the packages
apt-get remove -y $REMOVE
apt-get autoremove -y

# store new list of metapackages currently installed
dpkg -l | grep \ linux | grep ii | awk '{print $2}' | grep -v [0-9] > /tmp/$PID.packagelist.new

# if they're different, reinstall the missing metapackages
MISSING="`diff /tmp/$PID.packagelist.new /tmp/$PID.packagelist --left-column | cut -d' ' -f2 | grep linux`"
if [ "$MISSING" != "" ]
then
  INSTALL=""
  while read line
  do
    # make sure the package is actually missing first
    if [ "`dpkg -l | grep -v ^ii | grep $line`" != "" ]
    then
      INSTALL="$INSTALL $line"
    fi
  done   # if there are any missing packages, install them
  if [ "$INSTALL" != "" ]
  then
    apt-get install -y $INSTALL
  fi
fi

# clean up
rm /tmp/$PID.*