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Read only file system on Android

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android

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What is a read only file system?

Read-only is a file attribute which only allows a user to view a file, restricting any writing to the file. Setting a file to “read-only” will still allow that file to be opened and read; however, changes such as deletions, overwrites, edits or name changes cannot be made.


Not all phones and versions of android have things mounted the same.
Limiting options when remounting would be best.

Simply remount as rw (Read/Write):

# mount -o rw,remount /system

Once you are done making changes, remount to ro (read-only):

# mount -o ro,remount /system

adb remount

works for me and seems to be the simplest solution.


Got this off an Android forum where I asked the same question. Hope this helps somebody else.

On a terminal emulator on the phone:

mount -o rw,remount -t yaffs2 /dev/block/mtdblock3 /system

Then on the cmd prompt, do the adb push


While I know the question is about the real device, in case someone got here with a similar issue in the emulator, with whatever tools are the latest as of Feb, 2017, the emulator needs to be launched from the command line with:

-writable-system

For anything to be writable to the /system. Without this flag no combination of remount or mount will allow one to write to /system.

After the emulator is launched with that flag, a single adb remount after adb root is sufficient to get permissions to push to /system.

Here's an example of the command line I use to run my emulator:

./emulator -writable-system -avd Nexus_5_API_25 -no-snapshot-load -qemu

The value for the -avd flags comes from:

./emulator -list-avds