The question says it all. All folders on my sdcard has owner set as 0(root) and group set as sdcard_r - means all apps that have permissions to access the sdcard.

However, since I have root, I want to change the group of this folder using chgrp, so that only a selected app can access this. I know how to do this too, so no probs until now.

However, I don't want this to be a one-way setting, I want to be able to revert back to sdcard_r in case something goes wrong. Now I don't know the actual gid of this group sdcard_r and chgrp only works with gids, not names. So, how can I find the gid of this group, sdcard_r?

  • Weird, I don't even see a sdcard_r group listed in Root Explorer on my devices... – Andy Yan Oct 20 '16 at 10:57
  • What group do you see assigned to a random folder on sdcard (such as /mnt/sdcard/foo) in the root explorer? – Prahlad Yeri Oct 20 '16 at 13:06
  • 9997, which doesn't have a corresponding name in the list. – Andy Yan Oct 20 '16 at 14:11
  • k, and if you open a terminal app and go to the sdcard folder and perform ls -al, what group does it show there? (In my case its sdcard). – Prahlad Yeri Oct 20 '16 at 15:40
  • What does id sdcard_r and id -G sdcard_r returns? – Firelord Oct 20 '16 at 21:12

Use the following command to see GID of the concerned group:

id -G group_name

Courtesy of this answer of doylefermi.

It is very much possible that the GID would be 1028 given this line in source code of Android.

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