adb - can't mount android system partition as read/write -

i have android marshmallow running in emulator , executed following commands:

adb root adb mount -o remount,rw /system adb push file /system/file 

and output

adb: error: failed copy 'file' '/system/file': read-only file system 

the weird thing is, before remounting system partition mounted as

/dev/block/vda /system ext4 ro,seclabel,relatime,data=ordered 0 0 

and after remounting mounted as

/dev/block/vda /system ext4 rw,seclabel,relatime,data=ordered 0 0 

which seems read/writeable. after pushing

/dev/block/vda /system ext4 ro,seclabel,relatime,data=ordered 0 0 

again. weirder, system seems writable once:

root@generic_x86:/system # mount | grep system                                  /dev/block/vda /system ext4 rw,seclabel,relatime,data=ordered 0 0 root@generic_x86:/system # touch foo root@generic_x86:/system # touch foo2                                           touch: 'foo2': read-only file system root@generic_x86:/system # mount | grep system                                /dev/block/vda /system ext4 ro,seclabel,relatime,data=ordered 0 0  root@generic_x86:/system # ls -la foo*                                           -rw-rw-rw- root     root            0 2016-09-07 15:50 foo 

after have restart device because system partition can not remounted again.

noticed dmesg logs emulator using ranchu.fstab (can found @ android-studio/sdk/system-images/android-23/google_apis/x86) , not goldfish.fstab. so, in sdk folder of android studio (version 2.2) moved "kernel-ranchu" file elsewhere.

with change, when run emulator again (wipe emulator data), system partition stays "rw" , doesn't change "ro".

the reason tried because of io errors saw in dmesg logs while running emulator. not using ranchu fstab, partition names change /dev/block/vda /dev/block/mtd0 , on.

i not sure root cause of problem is, forcing emulator not pick ranchu.fstab seems have helped.