A ChromeOS upstart script to kick-off a crouton chroot desktop environment.

crouton.conf

# Copyright (c) 2016 The crouton Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

## Filename: /etc/init/crouton.conf
## NOTE: 'rootfs' verification needs to be removed.

## crouton chroot - Start session
##
## This will start a (crouton) chroot Desktop Environment session

description   "Crouton Chroot Session daemon"
author        "github/DennisLfromGA"

## Choose when the crouton chroot will be started - 4 choices below -
## NOTE: use only 1, prepend the others with the remark character: #

#start on starting ui          # 1st - starts when the user interface begins
                               #     + only 1 chroot will run in this mode
                               #     + must use XMETHOD: 'xorg'

#start on started ui           # 2nd - starts when the user interface appears
                               #     + only 1 chroot will run in this mode
                               #     + must use XMETHOD: 'xorg'

#start on login-prompt-visible # 3rd - starts when the login screen appears
                               #     + only 1 chroot will run in this mode
                               #     + must use XMETHOD: 'xorg'

 start on start-user-session   # 4th - starts when the user logs in - DEFAULT
                               #     + multiple chroots could run in this mode
                               #     + can use either XMETHOD: 'xiwi' or 'xorg'
                               #     + ensures user ~/Downloads is available

stop on stopping ui or starting halt or starting reboot

############################################################################
## NOTE: This job can be controlled externally by placing the file        ##
#+       'crouton.init' in the User's Downloads folder on a per User      ##
#+       basis or in the chroots parent folder per system with the        ##
#+       following six optional variables set:                            ##
#+  1) DELAY 2) CHROOT 3) START_DE 4) CHROOT_APP 5) XMETHOD 6) RUN_STATE  ##
##~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~##
#+ [ the 'env ' prefix must be omitted in the control file ]              ##
##~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~##
## Start of control file variables                                        ##
##~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~##
env DELAY=10            # delay desired number of seconds before starting ##
env CHROOT=xenial       # enter desired chroot to start                   ##
env START_DE=startxfce4 # enter desired Desktop Envirnoment to use        ##
env CHROOT_APP=none     # enter desired chroot application to run         ##
env XMETHOD=default     # enter temporary X-Window Envirnoment to use     ##
env RUN_STATE=y         # change to 'n' to disable running $CHROOT        ##
##~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~##
## End of control file variables                                          ##
############################################################################

##########################################################################
## System control parameters                                            ##
##~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~##
env DEBUG=on          # change to 'on' for DEBUGGING output             ##
env MASTER_SW=on      # change to 'off' to override running any $CHROOT ##
env MULTIPLES=on      # change to 'off' to allow running only 1 $CHROOT ##
##########################################################################

script
  
  PID="$$"
  touch /tmp/$UPSTART_JOB-$PID.log

  ## For output, use 'grep $PID /var/log/messages'
  LOGGER="logger -p local3.info -t $UPSTART_JOB($PID)"

  trap "$LOGGER '### Exiting...'" EXIT

  $LOGGER "###############"
  $LOGGER "### Starting..."
  if [ "$DEBUG" = 'on' ]; then
    exec >> /tmp/$UPSTART_JOB-$PID.log 2>&1
    set -x
    $LOGGER "*** DEBUGGING turned ON."
    $LOGGER "*** See '/tmp/$UPSTART_JOB-$PID.log' for output."
  else
    $LOGGER "*** DEBUGGING is OFF."
  fi

  if [ "$MASTER_SW" = "off" ]; then
  ## No chroots will run even if allowed by external control file(s).
    $LOGGER "!!! The MASTER_SW has been turned OFF"
    $LOGGER "No CHROOTS will run - period. Exiting."
    $LOGGER "###############"
    $LOGGER "### Ending....."
    $LOGGER "###############"
    exit 255
  fi

  MULTS="`pgrep -l crouton|head -n 1`"
  if [ "$MULTIPLES" = "off" ]; then
  ## Multiple chroots cannot be run when more than one user is logged in.
    if [ -n "$MULTS" ]; then
      $LOGGER "!!! MULTIPLE CHROOTS has been turned OFF"
      $LOGGER "No more CHROOTS will be run now. Exiting."
      $LOGGER "###############"
      $LOGGER "### Ending....."
      $LOGGER "###############"
      exit 255
    fi
  elif [ -n "$MULTS" ]; then
      $LOGGER "*** MULTIPLE CHROOTS is turned ON"
      $LOGGER "Now running an additional CHROOT."
      $LOGGER "###############"
  fi

  $LOGGER "##- Main checks started."
  if [ -d /var/crouton/chroots ]; then
  ## Uses the @drinkcat 'separate_partition' branch - as DEFAULT
    CROUTON_BIN=/var/crouton/bin
    CROUTON_CHROOTS=/var/crouton/chroots
  # if [ ! -x $CROUTON_BIN ]; then
      mount -i -o remount,exec /var
      $LOGGER "*** '/var' directory is being mounted as executable."
  # else
  #   $LOGGER "*** '$CROUTON_BIN' directory is already mounted as executable."
  # fi
    $LOGGER "###############"
  elif [ -d /usr/local/chroots ]; then
  ## Uses the @dnschneid 'master' branch
    CROUTON_BIN=/usr/local/bin
    CROUTON_CHROOTS=/usr/local/chroots
    $LOGGER "###############"
  else
  ## Nothing found...
    $LOGGER "*** Crouton 'chroots' directory is missing. Aborting!"
    $LOGGER "###############"
    exit 1
  fi

  if [ ! -d $CROUTON_BIN ]; then
    $LOGGER "*** Crouton 'bin' directory is missing. Aborting!"
    $LOGGER "###############"
    exit 1
  fi

  $LOGGER "*** Crouton 'bin' directory is $CROUTON_BIN"
  $LOGGER "*** Crouton 'chroots' directory is $CROUTON_CHROOTS"

  $LOGGER "##- Check for external control."
  USER_DOWNLOADS="/home/chronos/user/Downloads"
  DOWNLOADS_INIT="$USER_DOWNLOADS/${UPSTART_JOB}.init"
  CHROOTS_PARENT=`dirname $CROUTON_CHROOTS`
  CROUTON_INIT="$CHROOTS_PARENT/${UPSTART_JOB}.init"
  if   [ -r $DOWNLOADS_INIT ]; then INIT_FILE="$DOWNLOADS_INIT"
  elif [ -r $CROUTON_INIT ];   then INIT_FILE="$CROUTON_INIT"; fi
  if   [ -r $INIT_FILE ] && [ -s $INIT_FILE ]; then
    $LOGGER "*** External control enabled via '$INIT_FILE' file."
    ## Pull in variables from external control file
    Delay="`      awk -F= '/^DELAY=/      {print $2; exit}' "$INIT_FILE"`"
    Chroot="`     awk -F= '/^CHROOT=/     {print $2; exit}' "$INIT_FILE"`"
    Start_DE="`   awk -F= '/^START_DE=/   {print $2; exit}' "$INIT_FILE"`"
    Chroot_App="` awk -F= '/^CHROOT_APP=/ {print $2; exit}' "$INIT_FILE"`"
    XMethod="`    awk -F= '/^XMETHOD=/    {print $2; exit}' "$INIT_FILE"`"
    Run_state="`  awk -F= '/^RUN_STATE=/  {print $2; exit}' "$INIT_FILE"`"

    if [ -n "$Delay" -a "$Delay" != "$DELAY" ]; then
      $LOGGER "##* DELAY changed from: '$DELAY' to '$Delay'."
      DELAY="$Delay"
    fi

    if [ -n "$Chroot" -a "$Chroot" != "$CHROOT" ]; then
      $LOGGER "##* CHROOT changed from: '$CHROOT' to '$Chroot'."
      CHROOT="$Chroot"
    fi

    if [ -n "$Start_DE" -a "$Start_DE" != "$START_DE" ]; then
      $LOGGER "##* START_DE changed from: '$START_DE' to '$Start_DE'."
      START_DE="$Start_DE"
    fi

    if [ -n "$Chroot_App" -a "$Chroot_App" != "$CHROOT_APP" ]; then
      $LOGGER "##* CHROOT_APP: '$Chroot_App' will be executed."
      CHROOT_APP="$Chroot_App"
    else
      CHROOT_APP=
    fi

    if [ -n "$XMethod" -a "$XMethod" != "$XMETHOD" ]; then
      $LOGGER "##* XMETHOD changed from: '$XMETHOD' to '$XMethod'."
      XMETHOD=$XMethod
    elif [ "$XMETHOD" != "default" ]; then
      $LOGGER "##* XMETHOD changed from: 'default' to '$XMETHOD'."
    else
      $LOGGER "##* XMETHOD unchanged - set to '$XMETHOD'."
    fi

    if [ -n "$Run_state" -a "$Run_state" != "$RUN_STATE" ]; then
      $LOGGER "##* RUN_STATE changed from: '$RUN_STATE' to '$Run_state'."
      RUN_STATE="$Run_state"
    fi
  else
    $LOGGER "### NO external control file found, using internal defaults."
  fi

  $LOGGER "##- Secondary checks started."
  if [ ! -d $CROUTON_CHROOTS/$CHROOT ]; then
    $LOGGER "*** Crouton '$CHROOT' directory is missing. Aborting!"
    $LOGGER "###############"
    exit 1
  elif [ ! -s $CROUTON_BIN/$START_DE -o ! -x $CROUTON_BIN/$START_DE ]; then
    $LOGGER "*** Crouton '$START_DE' script is missing or not executable. Aborting!"
    $LOGGER "###############"
    exit 1
  fi

  case $XMETHOD in
    xorg|xiwi*)
      XMARG="-X $XMETHOD"
    ;;
    default)
      XMARG=
    ;;
    *)
      XMARG=
      $LOGGER "##* XMETHOD: '$XMETHOD' is invalid so not set."
    ;;
  esac

  if [ "$RUN_STATE" = "n" -o "$MASTER_SW" = off ]; then
    $LOGGER "*** The RUN_STATE for chroot '$CHROOT' is DISABLED. Exiting."
    $LOGGER "###############"
    exit 0
  fi

  $LOGGER "##- Starting main process in $DELAY seconds."
  sleep $DELAY

  $LOGGER "##$ $CROUTON_BIN/$START_DE -c $CROUTON_CHROOTS -n $CHROOT $XMARG $CHROOT_APP"
  eval sudo $CROUTON_BIN/$START_DE -c $CROUTON_CHROOTS -n "$CHROOT" $XMARG "$CHROOT_APP"

  $LOGGER "##- Completed: status $?"
  $LOGGER "### Ending....."
  $LOGGER "###############"

  if [ "$DEBUG" = "y" ]; then
    set +x
  fi

end script

Updated release to use 'xenial'.

Updated to mount /var as exec if needed.

Updated & improved mounting /var logic.