Unable to mount /system as read-write

Question

I want to modify a file under /system. The problem is that is read-only, and even with root I cannot set it as read-write.

I've tried the following:

• Root Explorer (the automatic button)
• A one click app (https://play.google.com/store/apps/details?id=com.blogspot.superthomaslab.mountsystemrorw)
• The following commands, on Terminal Emulator: su and after that mount -o rw,remount /system. Along with that some variants (specifiying -t, using -rw, mount -o rw,remount /system /system)

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Some useful informations:

• The device is a Redmi 3
• Using android 5.1.1, on MIUI 6.4.7 (china developer version)
• I have root access, and enabled it for the apps mentioned above
• Bootloader is unlocked
• No SD card
• Output of mount | grep system: /dev/block/dm-0 /system ext4 ro,seclabel,relatime,discard,data=ordered 0 0

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I would like to manage the /system folder directly from the phone. I'm pretty hopeless, I've tried googling 2 hours for a working solution. Thanks in advance.

Answer 1

I've found the source of the problem asking in the MIUI forums, the boot image will not accept a modified /system.

You have to use the adb interface: adb devices then adb disable-verity.

Disclaimer: I'm not responsible for any damage caused by these operations.

Answer 2

As suggested by user aalaap here, disabling Mount Namespace Separation setting in SuperSU solved this issue for me on ZP999 and SuperSU 2.82 SR5.