Does all root directory in android os exist in flashing firmware At the root directory of android os there is some folder such as /acct /root /sys /dev , ... that are not available in firmware structure. by using fastboot to flash firmware There is some mount point like /system /cust /recovery /boot but there is no (/) root mount point.
I want to flash whole OS. Is there any firmware that contains above directories such as (/) root?
or how can i restore my hole android to factory snapshot?
My phone is huawei g6-u10.
The root file system (/) and the files therein (plus several more in some sub-directories) are created at boot time from the so-called InitRd ("initial RAM disk", or "boot image").

Plus, there are some special "directories" which hold not really "files" but map system information (there's a Unix maxime saying "everything is a file"); in a terminal (or from adb shell) run the command mount, and you see some special file systems like sysfs and tmpfs: the former holds system information, the latter temporary stuff.

As those are created by InitRd, you don't need to worry about them being lost when flashing a new ROM: they weren't really there, and the boot image from the new ROM will take care of creating them properly as well.

For further details, please also refer to these posts on our site.