I'm running a rooted Android-6 Marshmallow media box.
To it I have a external USB drive attached, formatted as NTFS (I believe it's NTFS. It's been a long while since I set this up).
The drive is mounted as:
/mnt/media_rw/<15-digit-hex-number>
The permissions are currently rwxrwx--- (0x770)
I don't know what changed, but I used to be able to WRITE to that USB drive. No longer. Only READ is possible now. Similarly, the Android file manager app Root Explorer use to be able to freely change permissions on that top-level directory (to change it to 0x777) as well as to files and directories beneath it. Again, no longer.
As prescribed elsewhere, I incorporated the appropriated addition to the following system file:
/system/etc/permissions/platform.xml
[ ... snip ... ]
<permission name="android.permission.WRITE_EXTERNAL_STORAGE" >
<group gid="sdcard_r" />
<group gid="sdcard_rw" />
<group gid="media_rw" />
</permission>
<permission name="android.permission.WRITE_MEDIA_STORAGE" >
<group gid="sdcard_rw" />
<group gid="media_rw" />
</permission>
[ ... snip ... ]
I'm getting permission denied when I try to either WRITE access that directory (meaning enter into the USB drive); as well as when I use Root Explorer to relax permissions on that directory to gain access (also permission denied).
I didn't upgrade Android or anything like that. It just stopped working.
Does anyone have any suggestions on how to fix this issue?
Thank you in advance.
Not long after I posted this lengthy question did I, by chance, figure out the issue. That mount point has to be accessed via an alternate path/route:
/storage/<15-digit-hex-number>
I believe what happened is that, whereas the particular application accessing that folder could previously do so via the original path specified (in the Question), that path/route is, perhaps, somehow restrictive/special and that application suddenly started respecting that restriction (and therefore could no longer write via that original path). I just found this out by looking at a different application that writes to the same place, and noticed the alternate path/route it was using (i.e. the one above).
If you should run into this issue, try starting the path traversal at /storage/ instead.