"adb logcat" Command - Displaying System Logs

Android Tutorials - Herong's Tutorial Examples

∟Using "adb logcat" Command for Debugging

∟"adb logcat" Command - Displaying System Logs

This section describes the 'adb logcat' command that can be used to print out Android system log data for debugging purpose.

When developing new Android applications, you have to learn some tools to help you to debug the code. The primary debugging tool provided in the Android SDK is the Android Debug Bridge (ADB) program.

In previous tutorials, we learned how to use the following ADB commands:

"adb install/uninstall" - To install or uninstall an Android application package on the connected emulator or device.
"adb shell" - To provide a Unix shell interface to the connected emulator or device.
"adb push/pull" - To copy files or folders to or from the connected emulator or device.

ADB also has another very useful command that can be used to debug applications:

"adb logcat" - To print out log data from the connected emulator or device.

Let's starts the Android emulator and run the "adb logcat" command to see what can get:

C:\herong\>\local\android-sdk-windows\platform-tools\adb logcat

W/Zygote  (   37): Preloaded drawable resource #0x108022c \
   (res/drawable-hdpi/dialog_top_holo_dark.9.png) that varies with \
   configuration!!
D/dalvikvm(   37): GC_EXPLICIT freed 3K, 1% free 8601K/8643K, \
   paused 3ms+4ms
...
I/Zygote  (   37): ...preloaded 31 resources in 50ms.
D/dalvikvm(   37): GC_EXPLICIT freed 29K, 1% free 9028K/9091K, ...
...
I/dalvikvm(   37): System server process 77 has been created
I/Zygote  (   37): Accepting command socket connections
E/BatteryService(   77): usbOnlinePath not found
...
I/sysproc (   77): Entered system_init()
I/sysproc (   77): ServiceManager: 0x1e4ad0
D/SensorService(   77): nuSensorService starting...
I/SensorService(   77): Goldfish 3-axis Accelerometer
...
I/SystemServer(   77): Activity Manager
I/ActivityManager(   77): Memory class: 48
F/BatteryStatsImpl(   77): problem reading network stats
F/BatteryStatsImpl(   77): java.lang.IllegalStateException: \
   problem parsing idx 1
F/BatteryStatsImpl(   77): 	at com.android.internal.net. \
   NetworkStatsFactory.readNetworkStatsDetail \
   (NetworkStatsFactory.java:300)
F/BatteryStatsImpl(   77): 	at com.android.internal.net. \
   NetworkStatsFactory.readNetworkStatsDetail
   (NetworkStatsFactory.java:250) \
...
F/BatteryStatsImpl(   77): Caused by: java.io.FileNotFoundException: \
   /proc/net/xt_qtaguid/stats: open failed: ENOENT \
   (No such file or directory)
F/BatteryStatsImpl(   77): 	at libcore.io.IoBridge.open \
   (IoBridge.java:406)
F/BatteryStatsImpl(   77): 	at java.io.FileInputStream.<init> \
   (FileInputStream.java:78)
...
E/AndroidRuntime(   77): Error reporting WTF
E/AndroidRuntime(   77): java.lang.NullPointerException
E/AndroidRuntime(   77): 	at com.android.internal.os. \
   RuntimeInit.wtf(RuntimeInit.java:345)
E/AndroidRuntime(   77): 	at android.util.Log$1. \
   onTerribleFailure(Log.java:103)
E/AndroidRuntime(   77): 	at android.util.Log.wtf(Log.java:278)
...

^C

Note that:

It looks like the "adb logcat" command is printing all log data from the entire Android system.
Some log entries are providing general information like "W/Zygote ( 37): Preloaded drawable resource #0x108022c Preloaded drawable resource #0x108022c (res/drawable-hdpi/dialog_top_holo_dark.9.png"
Some log entries are reporting Java exceptions like "F/BatteryStatsImpl( 77): java.lang.IllegalStateException: problem parsing idx 1"
And there is even a null pointer exception in the AndroidRuntime code. See these 2 log entries: "E/AndroidRuntime( 77): java.lang.NullPointerException" and "E/AndroidRuntime( 77): at com.android.internal.os.RuntimeInit.wtf(RuntimeInit.java:345)"
You need to press "<Ctrl>-C" to stop "adb logcat" command. Otherwise it will continuously print new log data on the screen.