Help Android OS's and Micro SD card manipulation.

20GT · Jul 27, 2018

Android OS's and Micro SD card manipulation.

I have a new phone that has the Nougat OS. I've found that there is no way to manually manipulate the system files to alow an all apps or an individual app to freely use the SD card like back in the Jelly Bean days.

Going backwards in Android OS's which is the most up-to-date OS that is confirmed to allow this manipulation either as a whole or individually?

psionandy · Jul 27, 2018

Its rather manufacturer specific, rather than android version.

Some manufacturers have chosen to include the hooks requored for sd support, some have them but tweaks may have been required, some have removed them all together.

20GT · Jul 27, 2018

Is there a list of confirmed phones from the major manufacturers?

My stylo is LG and won't allow it.

All I want is an the is a newer OS that does this from either Samsung or LG it can be from an older phone so possibly cheaper.

Probably has to be a MetroPCS phone as well.

Any advice

Hadron · Jul 27, 2018

Let's just clarify what you want, because there are different questions about SD card usage.

I think you are asking about the ability of user-installed apps to write to SD. Before 4.4 any app could have full SD access, which was convenient but also a security risk (one app could modify another app's files). In 4.4 Google addressed this but went too far - unless you had root most apps couldn't write to the card at all. In 5.0 they introduced a mechanism by which you could grant apps full SD access, but the app has to request it. Many app developers did not do this, and still haven't. And if they don't you request it you cannot grant it.

Is that your problem?

If it is, I wasn't myself aware that any manufacturer had removed the access restrictions (though happy to be corrected). The only Samsung device I own is a tablet running 5.1, and that certainly has them (one of the apps I wanted to give this access to only requested it last year, several years after that option was added), and I don't own any LG devices.

psionandy · Jul 27, 2018

Thanks @Hadron

I may have been answering the similar, since jellybean, issue of using sd cards to store apps.

20GT · Jul 27, 2018

Hadron said:
In 5.0 they introduced a mechanism by which you could grant apps full SD access, but the app has to request it.

Please define "request". Does that mean actually request permission or just try to write to the SD card?

I was wrong my older phone was Kitkat. I was able to edit WRITE_EXTERNAL_STORAGE permission in platform.xml and obtain access.

Hadron said:
the app has to request it.

Isn't the app requesting it just code? a "flag" on a file? How does it know it requested it? Does it have to request it each particular time it wants to write to the SD card?

svim · Jul 27, 2018

20GT said:
...Isn't the app requesting it just code? a "flag" on a file? How does it know it requested it? Does it have to request it each particular time it wants to write to the SD card?

On a basic level when you're moving/copying files (or apps), the read/write permissions to a microSD card, or the internal storage for that matter, are managed and determined by the Android operating system running on your phone, not the apps. It's the operating system that directly interacts with your phone's hardware, the apps interact with the OS.

Hadron · Jul 27, 2018

Since platform.xml is a system file I assume you had root access to modify it.

The request is a one-off, in most apps I've used this with it is triggered by attempting to write, but I believe the developer could just make it an option in the app to request it. I don't know the internal details of how it works, but it opens a system dialogue where you select the top folder of the tree in which you wish to give the app write permissions (which if you choose the root of the SD card will be the whole card). It's clearly designed to require user interaction, presumably to stop an app developer just granting the app full access without the user knowing. I'm sure it's not a flag in a file, more likely something maintained in a system database. If you search for something like "sd card write access android 5" you'll find many examples of app developers explaining it to their users, such as this one.

I don't know whether anything in the mechanism changed in marshmallow or nougat, as I've never used an SD card with either. Nor do I know whether the same edit of platform.xml works in more recent operating systems (as with any system modification I'd back up the file to be modified first, and probably take a nandroid for good measure, before changing anything).

20GT · Jul 30, 2018

I've already tried editing the file and it doesn't work anymore

Here's some information about all the OS's and SD card permissions, but I'm not smart enough to know if it's something a rooted user can modify.

https://stackoverflow.com/questions...-to-write-to-external-sd-card-on-android?rq=1

Hadron · Jul 30, 2018

Just scanning it quickly while walking back from my train, my best guess for how to change it globally would be if you could change what sort of access /mnt/runtime/default gives. Though if a more recent app requested only read access that's all it would get. And no, I don't know how deep you'd have to dig to change this (I could imagine it requiring a kernel mod, but that's just speculation).

20GT · Jul 30, 2018

It wouldn't even have to be globally just a few apps

Hadron · Jul 30, 2018

The only way I can think of just doing it for a few apps would be to modify the apps.

Unless converting them to system apps does it - system apps do have full access, and Titanium Backup has a "convert to system app" option (at least the paid version does - I've never used the free one). But whether that's enough I don't know (I assume it just moves the app into /system, and as this phone isn't rooted I can't experiment) - you could only try.

(As with any system mod, I always recommend taking a nandroid first).

Help Android OS's and Micro SD card manipulation.

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