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ddms - a graphical debugging tool for Android
Dalvik Debug Monitor Service (DDMS) provides port-forwarding services, screen capture on
the device, thread and heap information on the device, logcat, process, and radio state
information, incoming call and SMS spoofing, location data spoofing, and more. This page
provides a modest discussion of DDMS features; it is not an exhaustive exploration of all
the features and capabilities.
DDMS will work with both the emulator and a connected device. If both are connected and
running simultaneously, DDMS defaults to the emulator.
How DDMS works
DDMS acts as a middleman to connect the IDE to the applications running on the device. On
Android, every application runs in its own process, each of which hosts its own virtual
machine (VM). And each process listens for a debugger on a different port.
When it starts, DDMS connects to adb and starts a device monitoring service between the
two, which will notify DDMS when a device is connected or disconnected. When a device is
connected, a VM monitoring service is created between adb and DDMS, which will notify DDMS
when a VM on the device is started or terminated. Once a VM is running, DDMS retrieves the
the VM's process ID (pid), via adb, and opens a connection to the VM's debugger, through
the adb daemon (adbd) on the device. DDMS can now talk to the VM using a custom wire
For each VM on the device, DDMS opens a port upon which it will listen for a debugger. For
the first VM, DDMS listens for a debugger on port 8600, the next on 8601, and so on. When
a debugger connects to one of these ports, all traffic is forwarded between the debugger
and the associated VM. Debugging can then process like any remote debugging session.
DDMS also opens another local port, the DDMS "base port" (8700, by default), upon which it
also listens for a debugger. When a debugger connects to this base port, all traffic is
forwarded to the VM currently selected in DDMS, so this is typically where you debugger
Tip: You can set a number of DDMS preferences in File > Preferences. Preferences are saved
Known debugging issues with Dalvik
Debugging an application in the Dalvik VM should work the same as it does in other VMs.
However, when single-stepping out of synchronized code, the "current line" cursor may jump
to the last line in the method for one step.
The left side of the Debug Monitor shows each emulator/device currently found, with a list
of all the VMs currently running within each. VMs are identified by the package name of
the application it hosts.
Use this list to find and attach to the VM running the activity(ies) that you want to
debug. Next to each VM in the list is a "debugger pass-through" port (in the right-most
column). If you connect your debugger to one of the the ports listed, you will be
connected to the corresponding VM on the device. However, when using DDMS, you need only
connect to port 8700, as DDMS forwards all traffic here to the currently selected VM.
(Notice, as you select a VM in the list, the listed port includes 8700.) This way, there's
no need to reconfigure the debugger's port each time you switch between VMs.
When an application running on the device calls waitForDebugger() (or you select this
option in the developer options), a red icon will be shown next to the client name, while
it waits for the debugger to attach to the VM. When a debugger is connected, the icon will
If you see a crossed-out bug icon, this means that the DDMS was unable to complete a
connection between the debugger and the VM because it was unable to open the VM's local
port. If you see this for all VMs on the device, it is likely because you have another
instance of DDMS running (this includes the Eclipse plugin).
If you see a question mark in place of an application package, this means that, once DDMS
received the application pid from adb, it somehow failed to make a successful handshake
with the VM process. Try restarting DDMS.
On the right side, the Debug Monitor provides tabs that display useful information and
some useful tools.
This view shows some general information about the selected VM, including the process ID,
package name, and VM version.
The threads view has a list of threads running in the process of the target VM. To reduce
the amount of data sent over the wire, the thread updates are only sent when explicitly
enabled by toggling the "threads" button in the toolbar. This toggle is maintained per
VM. This tab includes the following information:
ID a VM-assigned unique thread ID. In Dalvik, these are odd numbers starting from 3.
Tid the Linux thread ID. For the main thread in a process, this will match the process ID.
Status the VM thread status. Daemon threads are shown with an asterisk (*). This will be
one of the following:
running - executing application code
sleeping - called Thread.sleep()
monitor - waiting to acquire a monitor lock
wait - in Object.wait()
native - executing native code
vmwait - waiting on a VM resource
zombie - thread is in the process of dying
init - thread is initializing (you shouldn't see this)
starting - thread is about to start (you shouldn't see this either)
utime cumulative time spent executing user code, in "jiffies" (usually 10ms). Only
available under Linux.
stime cumulative time spent executing system code, in "jiffies" (usually 10ms).
Name the name of the thread
"ID" and "Name" are set when the thread is started. The remaining fields are updated
periodically (default is every 4 seconds).
Displays some heap stats, updated during garbage collection. If, when a VM is selected,
the VM Heap view says that heap updates are not enabled, click the "Show heap updates"
button, located in the top-left toolbar. Back in the VM Heap view, click Cause GC to
perform garbage collection and update the heap stats.
In this view, you can track the memory allocation of each virtual machine. With a VM
selected in the left pane, click Start Tracking, then Get Allocations to view all
allocations since tracking started. The table below will be filled with all the relevant
data. Click it again to refresh the list.
With these controls, you can simulate special device states and activities. Features
Telephony Status change the state of the phone's Voice and Data plans (home, roaming,
searching, etc.), and simulate different kinds of network Speed and Latency (GPRS, EDGE,
Telephony Actions perform simulated phone calls and SMS messages to the emulator.
Location Controls send mock location data to the emulator so that you can perform
location-aware operations like GPS mapping.
To use the Location Controls, launch your application in the Android emulator and open
DDMS. Click the Emulator Controls tab and scroll down to Location Controls. From here, you
- Manually send individual longitude/latitude coordinates to the device.
Click Manual, select the coordinate format, fill in the fields and click Send.
- Use a GPX file describing a route for playback to the device.
Click GPX and load the file. Once loaded, click the play button to playback the route
for your location-aware application.
When performing playback from GPX, you can adjust the speed of playback from the DDMS
panel and control playback with the pause and skip buttons. DDMS will parse both the
waypoints (<wpt>, in the first table), and the tracks (<trk>, in the second table, with
support for multiple segments, <trkseg>, although they are simply concatenated). Only
the tracks can be played. Clicking a waypoint in the first list simply sends its
coordinate to the device, while selecting a track lets you play it.
- Use a KML file describing individual placemarks for sequenced playback to the device.
Click KML and load the file. Once loaded, click the play button to send the coordinates
to your location-aware application.
When using a KML file, it is parsed for a <coordinates> element. The value of which
should be a single set of longitude, latitude and altitude figures. For example:
In your file, you may include multiple <Placemark> elements, each containing a
<coordinates> element. When you do so, the collection of placemarks will be added as
tracks. DDMS will send one placemark per second to the device.
Note: DDMS does not support routes created with the <MultiGeometry><LineString>lat1,
long1, lat2, long2, ...</LineString></MultiGeometry> methods. There is also currently
no support for the <TimeStamp> node inside the <Placemark>. Future releases may support
timed placement and routes within a single coordinate element.
With the File Explorer, you can view the device file system and perform basic management,
like pushing and pulling files. This circumvents using the adb push and pull commands,
with a GUI experience.
With DDMS open, select Device > File Explorer... to open the File Explorer window. You can
drag-and-drop into the device directories, but cannot drag out of them. To copy files from
the device, select the file and click the Pull File from Device button in the toolbar. To
delete files, use the Delete button in the toolbar.
If you're interested in using an SD card image on the emulator, you're still required to
use the mksdcard command to create an image, and then mount it during emulator bootup. For
example, from the /tools directory, execute:
$ mksdcard 1024M ./img $ emulator -sdcard ./img
Now, when the emulator is running, the DDMS File Explorer will be able to read and write
to the sdcard directory. However, your files may not appear automatically. For example, if
you add an MP3 file to the sdcard, the media player won't see them until you restart the
emulator. (When restarting the emulator from command line, be sure to mount the sdcard
You can capture screen images on the device or emulator by selecting Device > Screen
capture... in the menu bar, or press CTRL-S.
You can see the output of ps -x for a specific VM by selecting Device > Show process
status... in the menu bar.
Cause a GC to Occur
Cause garbage collection to occury by pressing the trash can button on the toolbar.
Running Dumpsys and Dumpstate on the Device (logcat)
To run dumpsys (logcat) from Dalvik, select Device > Run logcat... in the menu bar.
To run dumpstate from Dalvik, select Device > Dump device state... in the menu bar.
Examine Radio State
By default, radio state is not output during a standard logcat (it is a lot of
information). To see radio information, either click Device > Dump radio state... or run
logcat as described in Logging Radio Information.
Stop a Virtual Machine
You can stop a virtual machine by selecting Actions > Halt VM. Pressing this button causes
the VM to call System.exit(1).
If you connect and disconnect a debugger, ddms drops and reconnects the client so the VM
realizes that the debugger has gone away. This will be fixed eventually.
This manual page is licensed under the Apache License, Version 2.0.
Copyright (C) 2013 www.linuxtopia.org
Copyright (C) 2013 Jakub Adam <firstname.lastname@example.org>
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