remount of the / superblock failed: Permission denied

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System ：Android 9.0

Preface

　　　 When need is right userdebug When the version image is modified , We often use adb remount The implementation will vendor The partition is mounted to be readable and writable , However, permission errors will appear during operation remount of the / superblock failed: Permission denied, This chapter explains several common operation methods .

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Problem description

Mirror the system remount The operation of , You can use the following command ： 

adb root
adb remount

However, the following errors will occur ：

adb root
restarting adbd as root
$ adb remount
remount of the / superblock failed: Permission denied
remount failed

Common solutions  

Android 9 Then enabled avb(Android Verified Boot)2.0,verified boot and DM-verity, This function will check whether the system data is damaged , If the file has been modified , During startup, the startup will fail due to verification , It can be operated in the following ways ： 

adb root
adb disable-verity
adb reboot
adb root
adb remount 

At this time, if you still report the same error , You can try adb Enter the machine and do the following ： 

adb root

adb shell

# mount -o remount,rw /vendor

After this operation , There may also be the following error reports ： 

# mount -o remount,rw /vendor
 mount: '/vendor' not in /proc/mounts

Then the ultimate solution is ： 

cat /proc/mounts  | grep vendor                                                     
/dev/block/platform/a003e00.virtio_mmio/by-name/vendor /vendor ext4 rw,seclabel,relatime,block_validity,delalloc,barrier,user_xattr 0 0

Execute the reload command as follows ： 

mount -o remount,rw /dev/block/platform/a003e00.virtio_mmio/by-name/vendor