Refuse to change the chronos password if already set unless explicitly asked.

scripts/image_signing/set_chronos_password.sh

 #!/bin/bash
 
 # Copyright (c) 2010 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.
 
 # Customizes a Chrome OS release image by setting the chronos user password.
 
-# Usage: ./set_chronos_password.sh <image.bin> <chronos_password>
+# Usage: ./set_chronos_password.sh <image.bin> <chronos_password> [--force]
 
 # Load common constants and variables.
 . "$(dirname "$0")/common.sh"
 
 change_chronos_password() {
   local rootfs=$1
   local password=$2
   echo "Changing chronos password to '$password'..."
   local crypted_password="$(echo $password | openssl passwd -1 -stdin)"
   local temp_shadow="$rootfs/etc/tempshadow"
   echo "chronos:$crypted_password:14500:0:99999::::" \
     | sudo tee "$temp_shadow" > /dev/null
   sudo grep -Ev ^chronos: "$rootfs/etc/shadow" \
     | sudo tee -a "$temp_shadow" > /dev/null
   sudo mv -f "$temp_shadow" "$rootfs/etc/shadow"
 }
 
 main() {
   set -e
 
   local image=$1
   local chronos_password=$2
-  if [ $# -ne 2 ]; then
-    echo "Usage: $PROG <image.bin> <chronos_password>"
+  if [ $# -ne 2 ] && [ $# -ne 3 ] || [ ! $3 = "--force" ] ; then
+    echo "Usage: $PROG <image.bin> <chronos_password> [--force]"
     exit 1
   fi
 
-  local rootfs=$(mktemp -d)
+  local rootfs=$(make_temp_dir)
+  if [ $# -eq 2 ]; then
+    mount_image_partition_ro "$image" 3 "$rootfs"
+    if ! no_chronos_password "$rootfs"; then
+      echo "Password is already set [use --force if you'd like to update it]"
+      exit 1
+    fi
+    # Prepare for remounting read/write.
+    sudo umount -d $rootfs
+  fi
   mount_image_partition "$image" 3 "$rootfs"
-  trap "sudo umount -d $rootfs; rm -rf $rootfs" EXIT
   change_chronos_password "$rootfs" "$chronos_password"
   touch "$image"  # Updates the image modification time.
-  echo "Done."
+  echo "Password Changed."
 }
 
 main $@