[Solved] Android P (9.0) userdebug version failed to execute ADB remount

[DESCRIPTION]

On android P version if you follow ”
FAQ18076 android 6.0 M userdebug version failed to execute adb remount” on the userdebug version will prompt the following error.

remount of the/superblock failed: Permission denied

remount failed

The reason is that after android P version google enabled avb (
AndroidVerified Boot) 2.0, verified boot and DM-verity default enable policy has changed. Details are as follows.

DM-Verity behavior changes from vboot1.0 to avb2.0.

On vboot1.0, dm-verity is turned off on eng build and is enabled on userdebug/user build.

DM-verity could be disabled with adb (not fastboot) on userdebug build without unlocking device first.

DM-Verity could not be disabled on user build.

On avb2.0, dm-verity behavior are the same on all build variants.

It’s turned on by default and could only be disabled after device is unlocked.

dm-verity disable flag is moved from system image dm-verity metadata(vboot1.0) to vbmeta image(avb2.0), and you have two ways to disable it: adb and fastboot.


[SOLUTION]

* Android P + kernel-4.4 or kernel-3.18

– download preloader with verified boot disabled which location is the same as scatter file //preloader_<PROJECT>_SBOOT_DIS.bin

– adb root

– adb disable-verity

– adb reboot

– adb root

– adb remount

* Android P + kernel-4.9 or after
– download preloader with verified boot disabled which location is the same as scatter file. //preloader_<PROJECT>_SBOOT_DIS.bin
– boot to Home Screen
– go to setting -> system -> Developer options -> OEM unlocking
– adb reboot bootloader
– fastboot flashing unlock
– press volume up key
– fastboot reboot
– adb root
– adb disable-verity
– adb reboot
– adb root
– adb remount

After Android P, preloader_<PROJECT>_SBOOT_DIS.bin will be generated automatically after building preloader.

* Please note to download the latest adb/fastboot tool

Windows

https://dl.google.com/android/repository/platform-tools-latest-windows.zip

Mac

https://dl.google.com/android/repository/platform-tools-latest-darwin.zip

Linux

https://dl.google.com/android/repository/platform-tools-latest-linux.zip

refs;

https://ressrc.com/2018/09/21/android-p-how-to-enable-disable-security-boot/

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