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System Logs

Like any Linux based system, Android keeps a centralized structure of logs. Logging within the application is implemented with the Log class. There are varying levels of logs:

  • Log.d Debug log
  • Log.e Error log
  • Log.i Informational log
  • Log.v Verbose log
  • Log.w Warning log

Ironically, there is also a wtf log which stands for “What a Terrible Failure”. You will most likely never see this. To see more information about logs on Android, run adb logcat -h with a device attached to your computer.

Viewing Logs​

Obtaining the logs can be done with the logcat command!
On the device, you can simply run the following command which will dump the current logs:

logcat -d

To redirect it to a file on the device:

logcat -d -f /sdcard/logs.txt

From your computer, you simply prefix it with the adb command:

adb logcat -d

In most cases, you will want to limit the logs to the application under test. From your computer, you can pipe the logcat output to grep for further refinement.

adb logcat -d | grep -i appname 
adb logcat -d | grep -i appname > filename.txt

Review the output for any sensitive data. It is common to find sensitive data in the logs!

Review Source Code​

Once you have decompiled the APK file with jadx, you can search the “sources” directory for instances of the Log class:

grep -ri “Log.” sources