Unknown issue of modify a file in root, and app can't access that file. about libsu HOT 2 CLOSED

Psst.... I somehow missed a whole lot of text where you have already found the issue. As in my original reply, the app cannot access the file because the owner, group and permissions have changed.

You have two options:

1. su as the app's user - you can do this by getting the app's owner uX_aYYY and do the changes. Once you have su'ed as the user, you do not even require root anymore to modify the file since you act as the owner now. Im not sure if the shell will persist the su between Shell.sync.sh calls. But you can try.
   X - The user id. Usually 0 if there is no multi user on the phone or if the current user is the primary user
   Y - App id. I would guess android uses sequential numbers to generate this.

conclusively, the user is created for the app by u<userID>_a<appID> so perfect sandboxing is achieved across apps and different users

2. Copy the file to sdcard/your app dir and modify it as you are doing with cp now since it has solved the issue.

Also, you do not have to use cp to copy I believe. You can just use the File object to read the data in inputstream and flush it to target file using outputstream. But, cp is included in busybox which the library adds to your app. Read the original reply for more info

-------------------- Original Reply -----------------------------
I'm not in any way part of this library development but, I can put in my views.

First, is it possible that the direct modification has changed the owner and group or the file permissions? Each app has their user and group for sandboxing. If the group or owner is changed, its inaccessible by the original app anymore.

For cp I would assume it is safe because the library includes busybox by default unless you exclude it explicitly while building the app with this library included and busybox does contain cp.

from libsu.

@Yumeryu thanks for your report. The issue should be fixed since 1.3.0 release, can you update the library and check it out?

from libsu.