Question:
I need to run some commands that require higher privileges from the application on the root device. Say, for example, chmod 777 or access to a file whose permissions are --w------- (will work if the permissions were --w-----w- , which means that the application works as another group )
Additional information:
- Running Android API 18 (no SELinux)
Things I've already tried:
1) Using su from java :
From this post, I tried using su in java, for example:
Process su = null; try { su = Runtime.getRuntime().exec("su"); su.getOutputStream().write("chmod 777 file\n".getBytes()); su.getOutputStream().write("exit\n".getBytes()); su.waitFor(); } catch (Exception e) { e.printStackTrace(); } finally { if (su != null) { su.destroy(); } }
An error does not occur, but it does nothing.
2) Using setWritable() from java :
boolean ret = file.setWritable(true, false);
Here ret = false indicates that it failed.
3) Using the RootTools library:
Command cmd=new Command(0,"chmod 202 /sys/class/gpio/export"); try { RootShell.getShell(true).add(cmd); }catch(Exception e){ Log.d(TAG,e.getMessage()); }
Running this gives me: Error! Permission denied Error! Permission denied
4) Using this answer
Using the ExecuteAsRootBase class, I get: Can't get root access or denied by user .
5) Placing the application in /system/app
Still works like u0_a38 for this reason for some reason! To make this work, I had to manually place the .so library under /system/libs . I also had to chmod 644 my .apk so that it could work. I do not understand why I do not fall under root, as when I use ls -l on my apk in /system/app , it gives me:
-rw-r--r-- root root 1270817 2000-01-01 01:42 com.my.app.apk
6) Signing the application as a system application (not in /system/app )
That was the last thing I tried.
Following these instructions, I was able to sign and install the application. I called ps from the adb shell to check if it works as root, only to find out that it works under u0_a38 .
Note : when installing as a system application, even after signing, I could not install the application with android:sharedUserId="android.uid.shared" , because it gave me: Failure [INSTALL_FAILED_SHARED_USER_INCOMPATIBLE] . Thus, an application signed as a system application skipped this line from the manifest.
7) Placing the signed system application in /system/app
Just like in 5 .
When I enter ls -l in /system/app , I get:
-rw------- root root 1303459 2000-01-01 01:02 com.my.app.apk
However, running the "id" from the application, I know that it actually works like:
uid=10038(u0_a38) gid=10038(u0_a38) groups=1015(sdcard_rw),1028(sdcard_r),50038(all_a38)
8) Setting android:sharedUserId="android.uid.system" regardless of the error
So even if I could not make this installation using adb install due to an error: Failure [INSTALL_FAILED_SHARED_USER_INCOMPATIBLE] , I went ahead and pulled the trigger anyway. I used adb push to get .apk in /system/app , and then manually added my own library to /system/libs , rebooting the device so that the system would delete it. Then I got this error while loading:
W/PackageManager( 2652): Signature mismatch for shared user : SharedUserSetting{411d82d8 android.uid.system/1000} D/PackageManager( 2652): No files in app dir /vendor/app E/PackageManager( 2652): Package com.my.app has no signatures that match those in shared user android.uid.system; ignoring!
So, I assume that there is a possibility that the keys provided by the manufacturer may not be correct . I found them here , which is a link from the manufacturer’s website.
OR
This is a time ago, but not sure if it is still relevant. I hesitate to just delete this part of the file, but I will most likely end up trying it very soon. I do not see how uninstalling android.uid.***** from packages.xml will not affect applications already installed on the system.
Output:
Is there anything else that can be done besides rebuilding with new keys? Or is that almost all?