Don't set chronos default shell to bash.

chromeos/scripts/customize_rootfs

 #!/bin/bash
 
 # Copyright (c) 2011 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.
 
 # Script to customize the root file system after packages have been installed.
 #
 # NOTE: This is currently a dumping ground for for a bunch of hacks, some of
 # which are to work around the fact that we are trying not to modify the base
@@ skipping 50 matching lines @@
   echo "Error: Root FS does not exist? ($ROOT_FS_DIR)"
   exit 1
 fi
 
 # TODO: Is this still necessary?
 sudo chmod 0755 "${ROOT_FS_DIR}/."
 
 # Set up a default dev user, update the password entry, and add to sudo.
 # TODO: Make the default user conditional on building a dev image.
 DEV_USER="chronos"
-SHELL="/bin/sh"
-[[ -x "${ROOT_FS_DIR}/usr/local/bin/bash" ]] && SHELL="/usr/local/bin/bash"
-[[ -x "${ROOT_FS_DIR}/bin/bash" ]] && SHELL="/bin/bash"
 
 # Determine what password to use for the default user.
 CRYPTED_PASSWD_FILE="${SCRIPTS_DIR}/shared_user_passwd.txt"
 if [ -f $CRYPTED_PASSWD_FILE ]; then
   echo "Using password from $CRYPTED_PASSWD_FILE"
   CRYPTED_PASSWD=$(cat $CRYPTED_PASSWD_FILE)
 else
   # Use an invalid password so ensure pam_unix failure.
   echo "Using invalid password."
   CRYPTED_PASSWD='*'
 fi
 # Replace the DEV_USER passwd entry with one that sets the proper shell and
 # specifies that the passwd should come from /etc/shadow.
-sudo sed -i "{ s|${DEV_USER}:\*:\(.*\):.*|${DEV_USER}:x:\1:${SHELL}| }" \
+sudo sed -i "{ s|${DEV_USER}:\*:\(.*\):.*|${DEV_USER}:x:\1:/bin/sh| }" \
   "${ROOT_FS_DIR}/etc/passwd"
 echo "${DEV_USER}:${CRYPTED_PASSWD}:14500:0:99999::::" \
   | sudo dd of="${ROOT_FS_DIR}/etc/shadow" conv=notrunc oflag=append
 
 # sudo and vt2 are important for system debugging both in developer mode
 # and during development.  These two stanzas allow sudo and login auth
 # as user chronos under the following conditions:
 #
 # 1. password-less access:
 # - system in developer mode
@@ skipping 100 matching lines @@
     QEMU="qemu-i386"
     ;;
   *)
     error "Unable to determine ARCH from toolchain: $CHOST"
     exit 1
 esac
 cp "/usr/bin/${QEMU}" "${ROOT_FS_DIR}/tmp"
 sudo mkdir -p "${ROOT_FS_DIR}/usr/share/fontconfig"
 sudo chroot "${ROOT_FS_DIR}" "/tmp/${QEMU}" /usr/bin/fc-cache -f
 rm "${ROOT_FS_DIR}/tmp/${QEMU}"