[HELP]7840, no permission for adb action like umount /system or dd.

I just want to unbrick my device, and use the Phone Flash Tool Lite to Flash "Flash-DDO_BB.XML" and "Flash-IFWI-only.XML", then launch “IntelAndroid-FBRL-05-16-2015-PTR” to choose T4, and writing recovery and enter. then i found that i can't use command " umount /system" or "dd if=/..." , the error is permission is denied. What's wrong with it. Thanks a lot.