i have nexus 5 rooted, its version was 4.4 i tried to upgrade it to 6.0 so i download the ROM (image-hammerhead-mob30y) from developers.google.com and i copy the image to the phone by adb push command and when i try to install the image i get the error unable to mount storage. however i cant wipe internal storage or dalvik cache from the wipe section in TWRP. also every-time i try to get root access to the shell using 'su' command i get the error /sbin/sh: su: not found
so what can i do to install the image? if the issue with the image what did you recommenced?