Android SD card on emulator writing fails with IOException EROFS (Read-only filesystem), have correct permission

Question

My android app can't write a file to the AVD's SD card, here's the code:

    File root = Environment.getExternalStorageDirectory();

    Log.w("sdcard", "root.canWrite() = " + root.canWrite());

    try {           
        File myFile = new File(root + File.pathSeparator + "mysdfile.txt");
        myFile.createNewFile();
        FileOutputStream fOut = new FileOutputStream(myFile);
        OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
        myOutWriter.append("testing testing 123");
        myOutWriter.close();
        fOut.close();
    } catch (IOException e) {
        Log.w("ExternalStorage", "Error writing", e);
    }

root.canWrite() returns true, then this exception is raised:

java.io.IOException: open failed: EROFS (Read-only file system)

The manifest file has the WRITE_EXTERNAL_STORAGE permission (direct child of manifest):

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

I've also tried remounting the SD card in the AVD shell using:

mount -o remount rw /mnt/sdcard

...but to no avail. The AVD also has the "SD card support" flag set. Not sure what to do from here, any ideas?

Answer 1

Starting from Honeycomb, Android devices by default do not allow third-party apps from writing to external removable storage. You can check this by firing up your adb shell, go to /system/etc/permissions/platform.xml, and look for this line:

<permission name="android.permission.WRITE_EXTERNAL_STORAGE" >
    <group gid="sdcard_rw" />
</permission>

Third party apps are not part of "sdcard_rw" group, instead they're part of "media_rw". If your phone is rooted (your emulator should be), you can modify the platform.xml file to add another group that has this permission. It should look like this:

<permission name="android.permission.WRITE_EXTERNAL_STORAGE" >
    <group gid="sdcard_rw" />
    <group gid="media_rw" />
</permission>

Some manufacturers (I know Samsung does) that still have SD Card slots on their phones fixed this themselves, but not even Nexus 7 or GNex has this fixed by default.

Answer 2

To anyone interested, the problem was that I had made an sdcard.iso image and had eclipse passing that to the AVD as the -sdcard command line argument. For whatever reason, the image was read-only. Fixed the problem by clearing the command line args and editing the AVD to start with a new sd card of size 512mb, rather than a file.

Answer 3

In my case i have mistake with the slash. while specifying "Additional Emulator Command Line Options" in eclipse

Actually it should be -sdcard C:/Kamal/sdcard/emulator_sdcard

and i was putting -sdcard C:\\Kamal\\sdcard\\emulator_sdcard

Then after restarting the Eclipse & Emulator it works.

Answer 4

try {

  InputStream inputStream2 = openFileInput("database.sqlite3"); File outFile =new File(Environment.getExternalStorageDirectory(), "database15.sqlite3"); outFile.createNewFile(); OutputStream out= new FileOutputStream(outFile); byte[] buf = new byte[1024]; int len; while((len = inputStream2.read(buf))> 0) { out.write(buf); } out.close(); Toast.makeText(getBaseContext(),getFilesDir().toString()+"Done", Toast.LENGTH_LONG).show(); } catch (FileNotFoundException ex) { Toast.makeText(getBaseContext(),"file not found", Toast.LENGTH_LONG).show(); } catch (IOException e) { Toast.makeText(getBaseContext(),e.getMessage(), Toast.LENGTH_LONG).show(); }