vboot/utility/enable_dev_usb_boot

#!/bin/sh
# 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.

alert() {
  echo "$*" >&2
}

die() {
  alert "ERROR: $*"
  exit 1
}

case "$(crossystem fwid 2>/dev/null || true)" in
  Mario.* )
    die "Sorry, your platform does not support booting from USB."
    ;;

  Alex.* | ZGB.* )
    # For these legacy platforms, we need to re-flash firmware to get USB boot.
    chromeos-firmwareupdate --mode=todev || die "Failed to enable USB boot."
    ;;

  "" )
    die "Sorry, your firmware does not look like ChromeOS firmware."
    ;;

  * )
    crossystem dev_boot_usb=1 2>/dev/null || die "Failed to enable USB boot."
    echo "
    SUCCESS: Booting any self-signed kernel from SSD/USB/SDCard slot is enabled.

    Insert bootable media into USB / SDCard slot and press Ctrl-U in developer
    screen to boot your self-signed image.
    "
    ;;
esac