How to mount /system rewritable or read-only? (RW/RO)

Question

How can I mount the /system directory rewritable or read-only on my Android phone?

Answer 1

There are a few methods how you can mount your /system directory RW or RO. However, it will require root.

Method 1:

1. Connect your phone to the computer. (Make sure USB debugging is enabled on your phone)

2. Open CMD/Terminal on your PC.

   • Windows: CTRL + R, then type cmd.

   • Ubuntu: CTRL + ALT + T.

   • Mac: Navigate to /Applications/Utilities/ and double-click on Terminal.

3. Type this:

   1. adb shell

   2. su

   3. Choose one: (for security mount /system back to RO when finished)

      • Mount system RW: mount -o rw,remount /system
      • Mount system RO: mount -o ro,remount /system

Method 2:

1. Open terminal on your android phone (download here):

2. Type this in the terminal:

   1. su

   2. Choose one: (for security mount /system back to RO when finished)

      • Mount system RW: mount -o rw,remount /system
      • Mount system RO: mount -o ro,remount /system

Android 2.3

For people running Android 2.3 and the command fails, look at this answer: https://android.stackexchange.com/a/125437/95577

Answer 2

-writable-system for the emulator

When launching the emulator after a build with, you must use:

. build/envsetup.sh
lunch aosp_x86_64-eng
emulator -show-kernel -verbose -writable-system

Then, for future runs, you must keep the -writable-system option, or else image changes will not be visible:

emulator -show-kernel -verbose -writable-system

-verbose shows us that the emulator switches from the default -drive:

if=none,index=0,id=system,file=/path/to/aosp/8.1.0_r60/out/target/product/generic_x86_64/system-qemu.img,read-only

to:

if=none,index=0,id=system,file=/path/to/aosp/8.1.0_r60/out/target/product/generic_x86_64/system-qemu.img.qcow2,overlap-check=none,cache=unsafe,l2-cache-size=1048576

Therefore it:

• removes ,read-only

• uses system-qemu.img.qcow2 instead of system-qemu.img.

  This implies that changes will only be visible afterwards if you pass -writable-sytem on future boots after the change was made!

  We can see that the qcow2 image is just a small overlay on top of the base image since:

  qemu-img info /path/to/aosp/8.1.0_r60/out/target/product/generic_x86_64/system-qemu.img.qcow2
  

  contains:

  backing file: /path/to/aosp/8.1.0_r60/out/target/product/generic_x86_64/system-qemu.img
  

The emulator -help also confirms this:

emulator -help

contains:

-writable-system     make system & vendor image writable after 'adb remount'

adb remount + adb root

I think this is just a shortcut for mount as mentioned at https://android.stackexchange.com/a/110928/126934 , but it is very convenient:

adb root
adb remount
adb shell

adb help contains:

 root                     restart adbd with root permissions
 remount
     remount /system, /vendor, and /oem partitions read-write

Restore the original system image

Same as for userdata: remove the .qcow2 overlay, and re-generate it manually: https://stackoverflow.com/questions/54446680/how-to-reset-the-userdata-image-when-building-android-aosp-and-running-it-on-the

Answer 3

I really struggled with that until I used MT Manager (I tried a lot of root explorers and only MT Manager works for me). It isn't on Play Store, so you have to search for it online.

If it didn't work, try the Magisk module called OverlayFS. If you can't find it, here it is: OverlayFS (direct download from XDA).