[Q] Writing to and reading from /data/local?

---

I am creating a little app that will let a user read what's in a certain textfile in /data/local, edit it, and then save it. I have gotten everything to work by using some tutorials here and there, but there's still something not working.

Root access has been achieved, and writing/reading the file is done too, but when pressing the "Write" button, I get a toast saying "open failed: EACCES (Permission denied)". Google unfortunately didn't help me much on this one. Also, I am using the WRITE_EXTERNAL_STORAGE permission.

Code:

package bas.sie.hai;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.actionbarsherlock.app.SherlockActivity;

public class DataLocalActivity extends SherlockActivity {

    EditText txtData;
    Button btnReadSDFile;
    Button btnWriteSDFile;
    Button btnReadSkipFile;
    Button btnWriteSkipFile;
    Button btnClearScreen;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Process p;  
        try {  
           // Preform su to get root privledges  
           p = Runtime.getRuntime().exec("su");   

           // Attempt to write a file to a root-only  
           DataOutputStream os = new DataOutputStream(p.getOutputStream());  
           os.writeBytes("echo \"Do I have root?\" >/system/sd/temporary.txt\n");  

           // Close the terminal  
           os.writeBytes("exit\n");  
           os.flush();  
           try {  
              p.waitFor();  
                   if (p.exitValue() != 255) {  
                      // TODO Code to run on success  
                      Toast.makeText(this, "root", Toast.LENGTH_LONG);  
                   }  
                   else {  
                       // TODO Code to run on unsuccessful  
                       Toast.makeText(this, "No root", Toast.LENGTH_LONG);
                   }  
           } catch (InterruptedException e) {  
              // TODO Code to run in interrupted exception  
               Toast.makeText(this, "No root", Toast.LENGTH_LONG);  
           }  
        } catch (IOException e) {  
           // TODO Code to run in input/output exception  
            Toast.makeText(this, "NO root", Toast.LENGTH_LONG);  
        }  

        if(!Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())){
            Toast.makeText(this, "External SD card not mounted", Toast.LENGTH_LONG).show();
        }

        txtData = (EditText) findViewById(R.id.txtData);

        btnReadSDFile = (Button) findViewById(R.id.btnReadSDFile);
        btnReadSDFile.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // write on SD card file data in the text box
                try {
                    File myFile = new File("/data/local/move_cache.txt");
                    FileInputStream fIn = new FileInputStream(myFile);
                    BufferedReader myReader = new BufferedReader(
                            new InputStreamReader(fIn));
                    String aDataRow = "";
                    String aBuffer = "";
                    while ((aDataRow = myReader.readLine()) != null) {
                        aBuffer += aDataRow + "\n";
                    }
                    txtData.setText(aBuffer);
                    myReader.close();
                    Toast.makeText(getBaseContext(),
                            "Done reading from SD: 'move_cache.txt'",
                            Toast.LENGTH_SHORT).show();
                } catch (Exception e) {
                    Toast.makeText(getBaseContext(), e.getMessage(),
                            Toast.LENGTH_SHORT).show();
                }
            }
        }); 

        btnWriteSDFile = (Button) findViewById(R.id.btnWriteSDFile);
        btnWriteSDFile.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // write on SD card file data in the text box
                try {
                    File myFile = new File("/data/local/move_cache.txt");
                    myFile.createNewFile();
                    FileOutputStream fOut = new FileOutputStream(myFile);
                    OutputStreamWriter myOutWriter = new OutputStreamWriter(
                            fOut);
                    myOutWriter.append(txtData.getText());
                    myOutWriter.close();
                    fOut.close();
                    Toast.makeText(getBaseContext(),
                            "Done writing to SD: 'move_cache.txt'",
                            Toast.LENGTH_SHORT).show();
                } catch (Exception e) {
                    Toast.makeText(getBaseContext(), e.getMessage(),
                            Toast.LENGTH_SHORT).show();
                }
            }
        }); 

        btnReadSkipFile = (Button) findViewById(R.id.btnReadSkipFile);
        btnReadSkipFile.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // write on SD card file data in the text box
                try {
                    File myFile = new File("/data/local/skip_apps.txt");
                    FileInputStream fIn = new FileInputStream(myFile);
                    BufferedReader myReader = new BufferedReader(
                            new InputStreamReader(fIn));
                    String aDataRow = "";
                    String aBuffer = "";
                    while ((aDataRow = myReader.readLine()) != null) {
                        aBuffer += aDataRow + "\n";
                    }
                    txtData.setText(aBuffer);
                    myReader.close();
                    Toast.makeText(getBaseContext(),
                            "Done reading from SD: 'skip_apps.txt'",
                            Toast.LENGTH_SHORT).show();
                } catch (Exception e) {
                    Toast.makeText(getBaseContext(), e.getMessage(),
                            Toast.LENGTH_SHORT).show();
                }
            }
        }); 

        btnWriteSkipFile = (Button) findViewById(R.id.btnWriteSkipFile);
        btnWriteSkipFile.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // write on SD card file data in the text box
                try {
                    File myFile = new File("/data/local/skip_apps.txt");
                    myFile.createNewFile();
                    FileOutputStream fOut = new FileOutputStream(myFile);
                    OutputStreamWriter myOutWriter = new OutputStreamWriter(
                            fOut);
                    myOutWriter.append(txtData.getText());
                    myOutWriter.close();
                    fOut.close();
                    Toast.makeText(getBaseContext(),
                            "Done writing to SD: 'skip_apps.txt'",
                            Toast.LENGTH_SHORT).show();
                } catch (Exception e) {
                    Toast.makeText(getBaseContext(), e.getMessage(),
                            Toast.LENGTH_SHORT).show();
                }
            }
        }); 

        btnClearScreen = (Button) findViewById(R.id.btnClearScreen);
        btnClearScreen.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // clear text box
                txtData.setText("");
            }
        }); 


    }// onCreate

}

Thanks in advance,

Bas

Dooder

1. Chaper 8. Have mercy on yourself.
2. coloredlogcat.py
3. why not

e.printStackTrace()

but

Toast.LENGTH_SHORT

is beyond me
4.

android.permissions.WRITE_EXTERNAL_STORAGE

does not equal permissions to write to

 /data/local

5.

Google unfortunately didn't help me much on this one

Moment of honesty. G-FU sucks or you just gave up?

I am an a-hole for a reason here. All you need to know is out there. No one else will hit you harder on the head with a RTFM board than a coder.

Originally Posted by el_bhm

Dooder

1. Chaper 8. Have mercy on yourself.
2. coloredlogcat.py
3. why not

e.printStackTrace()

but

Toast.LENGTH_SHORT

is beyond me
4.

android.permissions.WRITE_EXTERNAL_STORAGE

does not equal permissions to write to

 /data/local

5.

Moment of honesty. G-FU sucks or you just gave up?

I am an a-hole for a reason here. All you need to know is out there. No one else will hit you harder on the head with a RTFM board than a coder.

The code is mostly from a tutorial, with a few edits. Why use stackTrace on a test? Also, I test on the device for reliability and root access. It's easier to see a Toast there, so didn't remove it.

About the Chapter 8: Yes, onClickListener is not the best way (skimmed over it, it's 1:26 AM here), but here too: optimizations later.

About Google: I Googled, didn't find anything that really could help me along so that I understood, asked in three other places. SO was someone who didn't reply later on, Google Groups said my permission was wrong, as I said WRITE_TO_EXTERNAL_STORAGE. I corrected that, saying I had the right permission but I wrote down the wrong one (hastily. Stupid, I know...), and here, on XDA, you're the only post yet. I have waited between posts to post it on all those boards, as I'm not an a**hole.

If any more information is needed, just tell me.

Bas

EDIT: Missed a bit. About the writing: I know now, it's just that I have no idea how to proceed from root access to writing there. And I do hope to learn how to do it.

1. You'd rather want to write into

/data/data/[package]/

Is there any particular reason you want to write directly to local? Some "system wide" app? From code I understand this is some tabbed app(?). Or is it just test for root?
Unless you have somewhat extensive knowledge of Linux and programming, don't go into root access. Make yourself a favour and get as much knowledge of objective programming first. It seems it was inspired by Outler doing root in part two. He's doing ADK in part 3. These are not easy things.

2. Are you sure you are writing anything? With this code I am getting nowhere actually.
I have not written anything with root (main reason it caught my attention). My best guess is though, permissions are not escalated for objects you are creating while setting up listeners for buttons.
From brief reading of the code and documentation it seems that you are escalating permissions for Process p which you works in conjunction with DataOutputStream. While setting up listeners you are not doing anything with p anymore.
My best guess permissions escalation would apply to the whole package, but as I see it, it does not happen.
EDIT: Besides, keep in mind you are writing a file via echoing through shell. Which is not equivalent of writing through instances of classes in onClickListeners

3. As to why printStackTrace()
Unless you are running Windows(which for Android development I really feel you should not) with coloredlogcat.py you'll have much more comprehensive output to troubleshoot the app. Line where problem occurs. Where it originates, where it goes, etc.
There should be some interpreter of python for Windows, but I don't know how the script will behave though.

4. Inserting logcat output is always helpful.
Providing the layout is always helpful.

Originally Posted by el_bhm

1. You'd rather want to write into

/data/data/[package]/

Is there any particular reason you want to write directly to local? Some "system wide" app? From code I understand this is some tabbed app(?). Or is it just test for root?
Unless you have somewhat extensive knowledge of Linux and programming, don't go into root access. Make yourself a favour and get as much knowledge of objective programming first. It seems it was inspired by Outler doing root in part two. He's doing ADK in part 3. These are not easy things.

2. Are you sure you are writing anything? With this code I am getting nowhere actually.
I have not written anything with root (main reason it caught my attention). My best guess is though, permissions are not escalated for objects you are creating while setting up listeners for buttons.
From brief reading of the code and documentation it seems that you are escalating permissions for Process p which you works in conjunction with DataOutputStream. While setting up listeners you are not doing anything with p anymore.
My best guess permissions escalation would apply to the whole package, but as I see it, it does not happen.
EDIT: Besides, keep in mind you are writing a file via echoing through shell. Which is not equivalent of writing through instances of classes in onClickListeners

3. As to why printStackTrace()
Unless you are running Windows(which for Android development I really feel you should not) with coloredlogcat.py you'll have much more comprehensive output to troubleshoot the app. Line where problem occurs. Where it originates, where it goes, etc.
There should be some interpreter of python for Windows, but I don't know how the script will behave though.

4. Inserting logcat output is always helpful.
Providing the layout is always helpful.

The files I'm writing are supposed to be in /data/local. Writing anywhere else would obviously kind of defeat the purpose.

I don't really have knowledge of Linux, didn't know you had to to be able to write a file. On the other hand, I had basically no knowledge of Android when I started writing my first app, and that worked out quite well, if I do say so myself.

About the permissions for the writing: I think you are right about that. I simply followed a tutorial, added SU permission check, and changed the path. Then tried to get that working.

I am running Windows. I do have Ubuntu on a bootable USB and on my HDD, but on the stick it has a low res and doesn't save any configs (which is not that weird), and on my HDD it suddenly fails to boot, and WUBI won't let me uninstall...
Plus, too much fiddling. Why is it so hard to get Flash installed, for God's sake?

About the LogCat output: I'm not really one to hook my phone up to my PC for that, unless no other solution is possible. Not because I'm lazy, but because my PC generally takes a couple of minutes to recognize the phone, open Explorer, etc. when I am doing a couple of other things.

I guess I'll just give up. Do you have any sites/places where I can gain some valuable knowledge about this?

Bas

About that permission check. Well, it passes the test. Thing is, there is no

/system/sd/temporary.txt

after I drop to adb shell.
Is that path the one you had set? IIRC Samsung does something funky with internal/external memory mounts in their devices. Is that path valid at all?
I'm guessing echo fails but passes the su test. So permissions are good, it seems.
Theoretically you can try parsing contents you need to that command you are basically executing. If there is a file in

/system/sd/

You could write file you need as temps wherever you have rights, then gain permissions and copy the contents via

cat [path_to_temp_file] > /data/local/file

Going offtopic.
Never. Ever use WUBI. Seriously. Just read about install process. If it fails on normal CD, download alternate. A bit more daunting but still should be manageable. Or get other distro like Mint.
It's enough to copy file to

~/.mozilla/plugins

. FF and Opera should easily use it.
Or just install

 ubuntu-restricte-extras

. It should have flash.

You can also get to your phone over wifi. Just get adbWireless from market.

Knowledge? On what?
Programming? Read documentation of android. Many tutorials. Really easy to read (compared to other OS docs), extensively described.
Stackoverflow
Get any O'reily books.
Android? See above.
Linux? Stop expecting from any distro to behave like Windows and use it as you would know nothing about PC. You'll save yourself much time and frustration.
webup8, omgubuntu, planet-ubuntu. Enough there to start.

Originally Posted by el_bhm

About that permission check. Well, it passes the test. Thing is, there is no

/system/sd/temporary.txt

after I drop to adb shell.
Is that path the one you had set? IIRC Samsung does something funky with internal/external memory mounts in their devices. Is that path valid at all?
I'm guessing echo fails but passes the su test. So permissions are good, it seems.
Theoretically you can try parsing contents you need to that command you are basically executing. If there is a file in

/system/sd/

You could write file you need as temps wherever you have rights, then gain permissions and copy the contents via

cat [path_to_temp_file] > /data/local/file

Going offtopic.
Never. Ever use WUBI. Seriously. Just read about install process. If it fails on normal CD, download alternate. A bit more daunting but still should be manageable. Or get other distro like Mint.
It's enough to copy file to

~/.mozilla/plugins

. FF and Opera should easily use it.
Or just install

 ubuntu-restricte-extras

. It should have flash.

You can also get to your phone over wifi. Just get adbWireless from market.

Knowledge? On what?
Programming? Read documentation of android. Many tutorials. Really easy to read (compared to other OS docs), extensively described.
Stackoverflow
Get any O'reily books.
Android? See above.
Linux? Stop expecting from any distro to behave like Windows and use it as you would know nothing about PC. You'll save yourself much time and frustration.
webup8, omgubuntu, planet-ubuntu. Enough there to start.

Well, this is intended for AOSP ROMs, so I was thinking that there shouldn't be any problem in trying to write a file in that directory. But yes, Samsung does do some weird things...

About the copying and then moving from there: Might be a good idea if I can figure it out. However, do you think that will suddenly work?

The install at first was planned to be from the bootable stick I have, but when I read about WUBI, it seemed so easy. Easy to deinstall Ubuntu, too. Anyhow, I think a friend kind of borked it not too long ago. Pressed the wrong button somewhere, might have slightly affected the MBR (Windows boot animation is also gone now, back to Vista :P).

Could you explain a bit more about the Flash install? It seemed (and truly was) so tedious at the time for something that was still slow and laggy... In my experience, don't get me wrong.

I have used AirDroid for example for reaching my phone, good suggestion there.

On the topic of developing (circling back around ), I will be looking into your suggestions. I do use Google and tutorials a lot, and SO has been quite a good help in that. Also, asking people to help personally (GTalk, for example, or PM on a forum), has got me quite a long way.

And using Ubuntu like I know nothing: It was quite different :P. I noticed that almost all of my knowledge was rendered useless in a matter of minutes haha. Bad thing is I did still think I knew, I guess. Led to frustration over it being so annoying. I guess it takes a lot of getting used to.

If that "temporary.txt" file is created, I don't see why it should fail since it passes the Root check.
instead of

cat

you may as well use

cp

which is basically command for copy.

About Flash (on which even Adobe is dropping a ball since they have balls to finally admit it's a joke anyway) you can read here.
https://help.ubuntu.com/community/RestrictedFormats

Alternate version of installer never failed me so far.

Originally Posted by el_bhm

If that "temporary.txt" file is created, I don't see why it should fail since it passes the Root check.
instead of

cat

you may as well use

cp

which is basically command for copy.

About Flash (on which even Adobe is dropping a ball since they have balls to finally admit it's a joke anyway) you can read here.
https://help.ubuntu.com/community/RestrictedFormats

Alternate version of installer never failed me so far.

I'll take a look at using cp. However, it might be some time before I pick this up again. My earlier project has almost been accepted by the person who asked me to make it, so first I'll be busy on that.
But the basic thing here is to create it somewhere else and copy it, right? Let's hope that works, then .

Also, I'll be looking at your suggestions for Flash and the alternate installer, thanks a lot!

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