A Chromebook init script to mount the CROUTON partition - made possible via @drinkcat's crouton/separate_partition branch

mnt-crouton.conf

# Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

description     "mount CROUTON on /var/crouton"
author          "drinkcat & DennisLfromGA"

start on starting boot-services
task
script
    # Exits the script with return code $1, spitting out message $@ to stderr
    error() {
        local ecode="$1"
        shift
        echo "$*" 1>&2
        exit "$ecode"
    }
    
    # Find the root device
    # Sets:
    #  - $ROOTDEVICE as the root device (e.g. /dev/sda or /dev/mmcblk0)
    #  - $ROOTDEVICEPREFIX as a prefix for partitions (/dev/sda, /dev/mmcblk0p)
    findrootdevice() {
        ROOTDEVICE="`rootdev -d -s`"
    
        if [ -z "$ROOTDEVICE" ]; then
            error 1 "Cannot find root device."
        fi
    
        if [ ! -b "$ROOTDEVICE" ]; then
            error 1 "$ROOTDEVICE is not a block device."
        fi
    
        # If $ROOTDEVICE ends with a number (e.g. mmcblk0), partitions are named
        # ${ROOTDEVICE}pX (e.g. mmcblk0p1). If not (e.g. sda), they are named
        # ${ROOTDEVICE}X (e.g. sda1).
        ROOTDEVICEPREFIX="$ROOTDEVICE"
        if [ "${ROOTDEVICE%[0-9]}" != "$ROOTDEVICE" ]; then
            ROOTDEVICEPREFIX="${ROOTDEVICE}p"
        fi
    }
    
    # Define CROUTON mountpoint
    MOUNTCROUTON='/var/crouton'
    # Try to mount the CROUTON partition, if it exists, on $MOUNTCROUTON.
    mountcrouton() {
        if [ -z "$ROOTDEVICE" ]; then
            findrootdevice
        fi
    
        local croutonpart="`sudo cgpt find -n -l CROUTON "$ROOTDEVICE"`"
        if [ -z "$croutonpart" ]; then
            return 1
        fi
    
        # Check if crouton is mounted already
        if grep -q "^${ROOTDEVICEPREFIX}$croutonpart " /proc/mounts; then
            # If mounted, it must be mounted to $mountpoint
    
            if ! grep -q "^${ROOTDEVICEPREFIX}$croutonpart $MOUNTCROUTON " \
                                                            /proc/mounts; then
                error 1 "Error: CROUTON partition is not mounted on $MOUNTCROUTON."
            else
                PRIOR=' already'
            fi
        else
            sudo mkdir -p "$MOUNTCROUTON" || error 1 "Cannot create $MOUNTCROUTON."
            sudo mount "${ROOTDEVICEPREFIX}$croutonpart" "$MOUNTCROUTON" || \
                error 1 "Cannot mount $MOUNTCROUTON"
        fi
        return 0
    }
    
    # Now mount the CROUTON partition
    mountcrouton
end script

For starting a crouton chroot auto-magically without entering the shell, see companion file crouton.conf.