Not able to write logcat output to a file within my app

Question

I am working on Android app in which I am trying to output the contents of logcat into a file on the sdcard.

I am aware of the fact that

From JellyBean 3P apps do not have access to system logs. However, I believe using logcat within my app, outputs atleast the log messages put out by my app.

Using WRITE_EXTERNAL_STORAGE permission in my manifest file.

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
try {
  //Code 1 - Seems like an app hang. Nothing shown.
  Process process = Runtime.getRuntime().exec("logcat -f /sdcard/mylog");

  //Code 2 - This works however if I run this alone, without the above. 
  FileWriter writer = new FileWriter("/sdcard/mylog");
  writer.append("test");
  writer.close();
}
  catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

I am testing my app on a device running kitkat.

What am I doing wrong here?

If it helps. You can read text at bottom at this link http://developer.android.com/tools/debugging/debugging-log.html. You can try to route output during phone or tablet lifecycle. But I am not sure about permissions needed for this. — busylee, Jul 04 '14 at 12:43

Hiemanshu Sharma · Answer 1 · 2014-07-04T11:27:01.600

0

When you run the command logcat it doesn't stop, it keeps running unless you ask it stop (Ctrl + C). You need to use logcat dump so that it dumps the logcat and stops.

logcat -d

This will dump the current contents of the logcat and finish once done.

Edit:

This wont work from the devise without root permissions anymore, starting from Jellybean.

edited Jul 04 '14 at 11:27

answered Jul 04 '14 at 11:12

Hiemanshu Sharma

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yes i tried that too. Using "logcat -d -f /sdcard/mylog" didn't seem to be helpful as well. – somesh Jul 04 '14 at 11:16
Oh, seems like it wont work from the device side anymore. You need root permission to be able to use logcat command now. – Hiemanshu Sharma Jul 04 '14 at 11:26
Did you set android.permission.READ_LOGS permission in your manifest file? – busylee Jul 04 '14 at 12:02
Hiemanshu, can you please quote the source where you found that info? busylee, yes I did. – somesh Jul 04 '14 at 12:20
@Hiemanshu, If it needs root permision to read log file on phone, how adb did it? I think it isn't right. – busylee Jul 04 '14 at 12:29
You can find the source here: http://nolanlawson.com/2012/09/02/catlog-jives-with-jelly-bean-goes-open-source/ Also adb has special permissions that individual apps dont. – Hiemanshu Sharma Jul 04 '14 at 12:32

score 0 · Answer 2 · edited May 23 '17 at 12:11

You can try this code:

try {
            Process process = Runtime.getRuntime().exec("logcat -f");

            Log.d("TAG", "my test phrase");

            BufferedReader bufferedReader = new BufferedReader(
                    new InputStreamReader(process.getInputStream()));

            StringBuilder log=new StringBuilder();
            String line;

            FileWriter fw = new FileWriter("/sdcard/mylog");

            while ((line = bufferedReader.readLine()) != null) {
                fw.append(line);
            }

            fw.close();
        } catch (IOException e) {
        }

This works for me. Hope it helps.

More info

Not able to write logcat output to a file within my app

2 Answers2