apache cassandra 1.0.8 IncompatibleClassChangeError vtable stub and AssertionError Added column does not sort as the last column

Today we will spend sometime to look into two errors and see if it is really something to concern about. The erros are thrown when apache cassandra version 1.0.8 is running. Okay, let's to the first error.

ERROR [ReadStage:1559] 2012-10-16 20:38:25,336 AbstractCassandraDaemon.java (line 139) Fatal exception in thread Thread[ReadStage:1559,5,main]
java.lang.IncompatibleClassChangeError: vtable stub
        at org.apache.cassandra.db.AbstractColumnContainer.getColumn(AbstractColumnContainer.java:134)
        at org.apache.cassandra.db.Memtable$6.computeNext(Memtable.java:402)
        at org.apache.cassandra.db.Memtable$6.computeNext(Memtable.java:384)
        at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:140)
        at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:135)
        at org.apache.cassandra.db.CollationController.collectTimeOrderedData(CollationController.java:93)
        at org.apache.cassandra.db.CollationController.getTopLevelColumns(CollationController.java:62)
        at org.apache.cassandra.db.ColumnFamilyStore.getTopLevelColumns(ColumnFamilyStore.java:1298)
        at org.apache.cassandra.db.ColumnFamilyStore.getColumnFamily(ColumnFamilyStore.java:1184)
        at org.apache.cassandra.db.ColumnFamilyStore.getColumnFamily(ColumnFamilyStore.java:1151)
        at org.apache.cassandra.db.Table.getRow(Table.java:375)
        at org.apache.cassandra.db.SliceByNamesReadCommand.getRow(SliceByNamesReadCommand.java:58)
        at org.apache.cassandra.service.StorageProxy$LocalReadRunnable.runMayThrow(StorageProxy.java:765)
        at org.apache.cassandra.service.StorageProxy$DroppableRunnable.run(StorageProxy.java:1224)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:662)

I guess this is really some fatal errors encountered. Let's check out what is IncompatibleClassChangeError means. From IncompatibleClassChangeError javadoc

Thrown when an incompatible class change has occurred to some class definition. The definition of some class, on which the currently executing method depends, has since changed.

Honestly, this is really odd, this error thrown out of no where and the jvm stopped. I guess nobody change the compiled apache cassandra code during the node instance is running. It certainly sounds odd but I guess when the data hold per node is huge, then strange thing start to happened. Now, let's get into stack trace and follow stack trace path.

Bottom three stack traces are pretty obvious, a new thread was started and execute by the thread pool executor. Then we have class StorageProxy. Within this class, there is a static class LocalReadRunnable which implement the abstract method LocalReadRunnable. It seem like it is trying to read a local node table row. The table eventually make calls to the column family to retrieve column. Tracing even deeper, at line 134 of class AbstractColumnContainer,  reveal that no exception is thrown from here. This is like a mystery! :) The stack trace analysis and observed jvm stopped shown something is wrong. Though I am not sure what went wrong but if you have any idea, please discuss it as a comment below.

Next we look to another error.

ERROR [CompactionExecutor:4] 2014-10-22 06:13:00,884 AbstractCassandraDaemon.java (line 139) Fatal exception in thread Thread[CompactionExecutor:4,1,main]
java.lang.AssertionError: Added column does not sort as the last column
        at org.apache.cassandra.db.ArrayBackedSortedColumns.addColumn(ArrayBackedSortedColumns.java:126)
        at org.apache.cassandra.db.AbstractColumnContainer.addColumn(AbstractColumnContainer.java:129)
        at org.apache.cassandra.db.AbstractColumnContainer.addColumn(AbstractColumnContainer.java:124)
        at org.apache.cassandra.db.ColumnFamilySerializer.deserializeColumns(ColumnFamilySerializer.java:148)
        at org.apache.cassandra.io.sstable.SSTableIdentityIterator.getColumnFamilyWithColumns(SSTableIdentityIterator.java:232)
        at org.apache.cassandra.db.compaction.PrecompactedRow.merge(PrecompactedRow.java:110)
        at org.apache.cassandra.db.compaction.PrecompactedRow.<init>(PrecompactedRow.java:97)
        at org.apache.cassandra.db.compaction.CompactionController.getCompactedRow(CompactionController.java:137)
        at org.apache.cassandra.db.compaction.CompactionIterable$Reducer.getReduced(CompactionIterable.java:102)
        at org.apache.cassandra.db.compaction.CompactionIterable$Reducer.getReduced(CompactionIterable.java:87)
        at org.apache.cassandra.utils.MergeIterator$ManyToOne.consume(MergeIterator.java:118)
        at org.apache.cassandra.utils.MergeIterator$ManyToOne.computeNext(MergeIterator.java:101)
        at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:140)
        at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:135)
        at com.google.common.collect.Iterators$7.computeNext(Iterators.java:614)
        at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:140)
        at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:135)
        at org.apache.cassandra.db.compaction.CompactionTask.execute(CompactionTask.java:173)
        at org.apache.cassandra.db.compaction.CompactionManager$1.call(CompactionManager.java:135)
        at org.apache.cassandra.db.compaction.CompactionManager$1.call(CompactionManager.java:115)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:662)

Again, this error pop out of nowhere, during node operation, this exception just thrown. So now, we will look into what happened using the stack trace given. Similar to the above, bottom three stack traces are pretty obvious, a new thread was started and execute by the thread pool executor. It is a compaction thread and when compacting sstable, things break. Then row get reduced and columns get deserialized. When columns are re-formation, it throw an exception as the column does not sort. This is another strange phenomenon. It should have been sort before anyway but it is not. The javdoc for this method addColumn

AddColumn throws an exception if the column added does not sort after the last column in the map. The reasoning is that this implementation can get slower if too much insertions are done in unsorted order and right now we only use it when *all* insertion (with this method) are done in sorted order. The assertion throwing is thus a protection against performance regression without knowing about (we can revisit that decision later if we have use cases where most insert are in sorted order but a few are not).

It seem that this is probably reproducible during development environment as a few are not.. I guess this is not as fatal as previous error. That's it for this analysis, please give your inputs or comments if you have workaround.

---

 

UPDATE:

It seem that the second error is fix in https://issues.apache.org/jira/browse/CASSANDRA-5856

Android first application hello world

First Off, Happy New Year Everybody!

Perhaps there are ten or even hundreds of first application develop using android if you google. Well today, I will share mine too, hey, start of year, a hello world would be nice too. :) If you have programming skill in java and using eclipse IDE, then you come to this right place. In this article, I will use eclipse IDE and develop a hello world android application. I figured it was a painless few steps setup but it took me several days to get everything going due to my hectic life and problems encountered during this learning journey. I hope with these explain, you will have better and easier learning experience than I did.

This article assume you have read and had setup the Android Developer Toolkit plugin into eclipse IDE and Speed up android emulator startup in eclipse. If you have not, please refer to this link and this link respectively. Okay, let's get started as I will show project creation in steps with screenshots. I will document and describe my learning experience below but if you want to read further on certain topics, you can refer on the official documentation, then please refer to this link.

1. create a new android application project. If it is not listed in the tab File, try Other... ;)





2. Click Next button, it is a window to configure the new android application project. Here fill in the information which as such for this introduction course.



3. Click Next button, yet another window to configure the project. The default settings will work mostly fine for this introductory course.



4. Click next button, this is a setting for the application icons. I'm not a color person but this colors design works like a charm for me. :-) if you want to take the challenge, try change the default icon.



5. Click next button, the default Black Activity just fine to display the text hello world later.



6. Click next button, again, the default configuration work just fine. This is the last configuration.



7. Click finish button and now check your workspace, it should have created all the necessary files.

I remembered the first time I have setup, the tutorial never mentioned about installing android support libraries, so once Finish button was click, the project created with errors. This is a big of learning curve for something who is new to android. Let alone to say if you are new to java or even IDE. See screenshot below.



For your information, this project require a support library which is available in Android SDK manager. Okay, now, let's install android support library. On eclipse tab, click on Window and then Android SDK Manager. Find out where is the android support library and install it. See the screenshots below, it should give you sufficient of information to get this done.



 

 By now, eclipse will request you to restart, hence, restart your eclipse. Once restarted, you should see a new project known as appcompat_v7 exists in the Package Explorer window. If you project is still contain error, check if your project is build automatically. You can click on eclipse menu tab, Project then Build Automatically... is checked. The project should contain no error and if there is still error, in the eclipse, click on Problems tab and identify what is the error. Because error is dependent on your platform and version of eclipse and/or android sdk, hence, if you have problem, google and fix them. This is left for your exercises. If everything is okay, your project should be as similar as mine such as below.



Okay, now check the project properties make sure everything is okay.



As you can notice above, I have also install Android 4.4W.2 sdk for my learning journey, but I have enabled Android 5.0 for this project. The reference project appcompat_v7 is valid and exists. Both of android projects are free from any errors. So far so good.

Note, there is a directory known as gen and educated guess said it is automatic generated files. As such, you should not modify directory to the file within this gen package but leave it automatically generated. Please note, R.java must autogenerated for this project to compiled successfully for our next journey and if you do not see this file, then you should be worry and find out where and what is the problem why R.java never get generated. Hint, don't try to add into an invalid R.java from somewhere but fix the root cause here.

Just before we launch the application in android emulator, let's see some android files here.



So all looking good, it should be ready now to launch this hello world android application in android emulator. Just like launching a simple java app, the sequence is pretty much the same for android. Right click on the project, then click on Run As / Debug As. Since this is the first android application, you might have not configured Android Virtual Device (avd), you should by now configure one. If you have done the previous article, Speed up android emulator startup in eclipse. It should be a breeze here and just select this avd. If not, you can follow the procedures using the screenshots below.



Because the startup emulator is slow, I would suggest to leave the emulator running as long as you are learning to develop the application. Because starting the emulator in my workstation took minutes. As seen in the output below, I have configured two different avd and the output of one screenshot shown My First App is shown in the android menu. Cool!



Try click on My First App through the emulator, it should hello world. :-) That's it for this learning experience and I hope you learn something and if you want to contribute back, you can do so by donating back.

Thank you.

apache cassandra 1.0.8 out of memory error unable to create new native thread

If you are using apache cassandra 1.0.8 and having the exception such as below, you may want to further read. Today, we will investigate on what this error means and what can we do to correct this situation.

ERROR [Thread-273] 2012-14-10 16:33:18,328 AbstractCassandraDaemon.java (line 139) Fatal exception in thread Thread[Thread-273,5,main]
java.lang.OutOfMemoryError: unable to create new native thread
        at java.lang.Thread.start0(Native Method)
        at java.lang.Thread.start(Thread.java:640)
        at java.util.concurrent.ThreadPoolExecutor.addIfUnderMaximumPoolSize(ThreadPoolExecutor.java:727)
        at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:657)
        at org.apache.cassandra.thrift.CustomTThreadPoolServer.serve(CustomTThreadPoolServer.java:104)
        at org.apache.cassandra.thrift.CassandraDaemon$ThriftServer.run(CassandraDaemon.java:214)

This is not good, the application crashed with this error during operation. To illustrate this environment, it is running using oracle java 6 with apache cassandra 1.0.8. It has 12GB of java heap assigned with stack size 128k, max user processes 260000 and open files capped at 65536.

Investigate into the java stack trace, reveal that, this error is not thrown by java code but native code. Below is the trace path.

1. https://github.com/apache/cassandra/blob/cassandra-0.8/src/java/org/apache/cassandra/thrift/CassandraDaemon.java#L214


2. https://github.com/apache/cassandra/blob/cassandra-1.0.8/src/java/org/apache/cassandra/thrift/CustomTThreadPoolServer.java#L104


3. ThreadPoolExecutor.java line 657
   


4. ThreadPoolExecutor.java line 727
   


5. Thread.java line 640
   

A little explanation before we delve even deeper. Number 3 to 5, is jdk dependent. Hence, if you are using openjdk, the line number may be different. As mentioned early, I'm using oracle jdk. Unfortunately, it is not available online for browsing but you can download the source from oracle site.

Because this is a native call, we will look into code that is not in Java. If the following code looks alien to you, it sure looks alien to me as it is probably written in c++. If you have also notice, this code is taken from openjdk and it is not found in the oracle jdk. Probably it is a closed source but we will not go there. Let's just focus where this error thrown from and why. It is taken from here and the explanation here.

JVM_ENTRY(void, JVM_StartThread(JNIEnv* env, jobject jthread))
  JVMWrapper("JVM_StartThread");
  JavaThread *native_thread = NULL;

  // We cannot hold the Threads_lock when we throw an exception,
  // due to rank ordering issues. Example:  we might need to grab the
  // Heap_lock while we construct the exception.
  bool throw_illegal_thread_state = false;

  // We must release the Threads_lock before we can post a jvmti event
  // in Thread::start.
  {
    // Ensure that the C++ Thread and OSThread structures aren't freed before
    // we operate.
    MutexLocker mu(Threads_lock);

    // Since JDK 5 the java.lang.Thread threadStatus is used to prevent
    // re-starting an already started thread, so we should usually find
    // that the JavaThread is null. However for a JNI attached thread
    // there is a small window between the Thread object being created
    // (with its JavaThread set) and the update to its threadStatus, so we
    // have to check for this
    if (java_lang_Thread::thread(JNIHandles::resolve_non_null(jthread)) != NULL) {
      throw_illegal_thread_state = true;
    } else {
      // We could also check the stillborn flag to see if this thread was already stopped, but
      // for historical reasons we let the thread detect that itself when it starts running

      jlong size =
             java_lang_Thread::stackSize(JNIHandles::resolve_non_null(jthread));
      // Allocate the C++ Thread structure and create the native thread.  The
      // stack size retrieved from java is signed, but the constructor takes
      // size_t (an unsigned type), so avoid passing negative values which would
      // result in really large stacks.
      size_t sz = size > 0 ? (size_t) size : 0;
      native_thread = new JavaThread(&thread_entry, sz);

      // At this point it may be possible that no osthread was created for the
      // JavaThread due to lack of memory. Check for this situation and throw
      // an exception if necessary. Eventually we may want to change this so
      // that we only grab the lock if the thread was created successfully -
      // then we can also do this check and throw the exception in the
      // JavaThread constructor.
      if (native_thread->osthread() != NULL) {
        // Note: the current thread is not being used within "prepare".
        native_thread->prepare(jthread);
      }
    }
  }

  if (throw_illegal_thread_state) {
    THROW(vmSymbols::java_lang_IllegalThreadStateException());
  }

  assert(native_thread != NULL, "Starting null thread?");

  if (native_thread->osthread() == NULL) {
    // No one should hold a reference to the 'native_thread'.
    delete native_thread;
    if (JvmtiExport::should_post_resource_exhausted()) {
      JvmtiExport::post_resource_exhausted(
        JVMTI_RESOURCE_EXHAUSTED_OOM_ERROR | JVMTI_RESOURCE_EXHAUSTED_THREADS,
        "unable to create new native thread");
    }
    THROW_MSG(vmSymbols::java_lang_OutOfMemoryError(),
              "unable to create new native thread");
  }

  Thread::start(native_thread);

JVM_END

As I don't have knowledge in cpp, hence, there is no analysis into this snippet above, but if you understand what it does, I will be happy if you can give your analysis as a comment below of this article. It certainly looks to me that the operating system cannot create a thread at this point due to a few errors, JVMTI_RESOURCE_EXHAUSTED_OOM_ERROR and / or JVMTI_RESOURCE_EXHAUSTED_THREADS. Let's google to find out what is that supposed to mean. Below are some which is interesting.

• http://www.oracle.com/technetwork/java/hotspotfaq-138619.html#threads_oom


• http://www.onkarjoshi.com/blog/209/using-xss-to-adjust-java-default-thread-stack-size-to-save-memory-and-prevent-stackoverflowerror/


• http://www.odi.ch/weblog/posting.php?posting=411


• http://www.avricot.com/blog/?post/2010/05/03/Get-started-with-java-JVM-memory-%28heap%2C-stack%2C-xss-xms-xmx-xmn...%29


• https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-2.html#jvms-2.5.2

To summarize the analysis from the links above.

• stack is created when thread is created and when more threads are created, hence the total of stacks also increased as a result.


• A Java Virtual Machine stack stores frames. A Java Virtual Machine stack is analogous to the stack of a conventional language such as C: it holds local variables and partial results, and plays a part in method invocation and return.


• Java stack is not within of java heap, hence, even if you increase java heap to the cassandra via parameter -Xms or -Xmx, this error will happen again if the condition is met again in the future.


• If Java Virtual Machine stacks can be dynamically expanded, and expansion is attempted but insufficient memory can be made available to effect the expansion, or if insufficient memory can be made available to create the initial Java Virtual Machine stack for a new thread, the Java Virtual Machine throws an OutOfMemoryError.

Until current analysis, it certainly looks to me that when cassandra instance trying to create a new thread, it was not able to. It was not able to because the underlying operating system cannot create the thread due to two errors. It actually looks like the operating system does not have sufficient memory to create the thread, hence increasing -Xms or -Xmx will not solve the problem. Note that the file descriptor set in this case is not met neither as most of the criterias pretty much infinite.

It's pretty interesting to note that, if such error is thrown, to solve the problem is to decrease the -Xss or even the heap -Xms and -Xmx. Although I don't understand the logic behind of such method used, perhaps you should try but I seriously doubt so. If cassandra node has high usage of heap, decreasing heap will only create another type of problem.

If you know or have encountered such problem before and has a good fix, please leave the comment below this article. To end this article, there is currently as of this writing, a discussion happen at cassandra mailing list.

Speed up android emulator startup in eclipse

When exploring hello world android development app in eclipse, the emulator just painfully slow to even launch. To me, the speed matter because if it is slow, the test and development cycle will be affected and thus, the development experience will not be pleasant. So today, before we go into hello world article, we will first explore if it is possible to improve the speed of android emulator startup in eclipse.

I have google and found a few links, there are as of following.

• https://software.intel.com/en-us/android/articles/speeding-up-the-android-emulator-on-intel-architecture


• http://stackoverflow.com/questions/1554099/why-is-the-android-emulator-so-slow


• http://www.developer.com/ws/android/development-tools/supercharge-your-android-emulator-speed-with-intel-emulation-technologies.html


• http://askubuntu.com/questions/283972/how-to-speed-up-the-android-emulator-in-ubuntu-12-10


• http://techtach.com/2014/05/boost-android-emulator-performanceon-linux-speeding-up-android-emulator-on-ubuntu/


• http://delphi.org/2013/11/8-tips-to-speed-up-your-android-arm-emulator-avd/


• https://www.virag.si/2012/10/speeding-up-android-emulator/


• http://ubuntuforums.org/showthread.php?t=2160567


• https://www.infinum.co/the-capsized-eight/articles/is-your-android-emulator-just-too-slow


• http://blogs.nuxeo.com/development/2011/10/speeding-up-the-android-emulator/

To summarize the solution used to the links above, there are Intel Hardware Accelerated Execution Manager (HAXM), linux kvm or virtualbox, android virtual device (AVD) snapshot, increase device ram, GPU acceleration, disable antivirus ?!, 3rd party android emulator, using actual android device instead of emulator, etc.

Because every developer has different development environment and every sdk and improvement over time may render these method describe later in this article invalid. Thus, the speed gain in your environment when android emulator start may vary and thus create unnecessary confusion. Thus, you should always read on the links and find a solution that work best in your environment. The following steps improved my environment in such a way.

1. Before it start need 10minutes and then even after waited 10minutes, then it crashed. With this, on my i3 intel cpu, with 8GB of ram, the speed increase in within less than 2minutes and response is emulator is manageable.


2. The emulator start over time is persistence. There are situation when once the android virtual device is created, the second time it boot, the android screen in the emulator get gibberish and unclickable. So with my method describe later, this will not be a problem.

Before we go into the solution, let's understand what emulator is. Emulator according to wikipedia

In computing, an emulator is hardware or software or both that duplicates (or emulates) the functions of one computer system (the guest) in another computer system (the host), different from the first one, so that the emulated behavior closely resembles the behavior of the real system (the guest).

In android sense, this emulator actually emulate a smartphone environment including hardware instruction, from workstation cpu x86 to the android device which uses arm. Because of Android Emulator emulates a real ARM processor on top of an x86 processor, this create a lot of overhead. Connection of real device through usb via eclipse integration is not available for linux environment. Thus, for initial learning phase, a android emulator is a good start.



Launch Android Virtual Device Manager from eclipse.



create a new android virtual device, as seem below with this setting.



As you can see, the target for the application is being currently latest at Android 5.0 - API Level 21. The important part now is to choose CPU/ABI to Intel Atom(x86_64). Of cause smartphone device mostly with arm cpu but as mentioned previously, we want emulator be a quick test environment.

If you notice, I have left Use Host GPU uncheck. When this is check with my environment, there is no speed up and when the android evironment started, the colour became gibberish and not clickable. Now start the device and experience the clicking in the environment.

Happy develop in android.

 

Setting up eclipse with Android development environment

Today, we will explore something different. Android is a very well known brand in the public now and can be found in devices such as smartphone, tablet, wearable like watch and glass, any end user device like tv or smart appliances. So we will take a look from programming point of view. This is a fresh start article and if you come from java development background and has zero knowledge on android development then this is an article for you. More on android development articles will come later.

To reduce the learning curve and to have a better learning and development experience in android, you should really setup android developer toolkit plugin in an IDE. If you have been develop Java for sometime now, IDE such as eclipse or netbeans should come in mind. Eclipse has always been my favourite IDE for java development and in this article, I will share on how to install ADT plugin in eclipse for android environment.

This article is based on this instruction. You should refer that for any changes or error encountered if you read this article in the future. As of this writing, I'm using eclipse luna for this ADT plugin installation. Let's start the installation.

1. Launch eclipse and click Help then Install New Software... then click on Add button.


2. We will add ADT plugin repository to this eclipse IDE. In the pop up window, add as following and then click on OK.
   Name: ADT Plugin
   Location: https://dl-ssl.google.com/android/eclipse/
   


3. Wait a while for the update to pull in by eclipse and the in the Available Software dialog, select the checkbox next to Developer Tools and click on Next.
   


4. In the next window, you'll see a list of the tools to be downloaded. Click Next.


5. Read and accept the license agreements, then click Finish.
   If you get a security warning saying that the authenticity or validity of the software can't be established, click OK.


6. When the installation completes, restart Eclipse.


7. Once Eclipse restarts, you must specify the location of your Android SDK directory. Because this is a new installation, there is no android sdk installed and click on Open Preferences.
   


8. In the "Welcome to Android Development" window that appears, select Install new SDK. Then wait until the installation is complete.
   
   


9. When sdk is installed, a new window popup requesting to install new build tool. Click on Open SDK Manager.
   


10. There are preselected build-tools and as of this moment, just accept the default preselected tools and click Install button. We can install more tools later.
    


11. Wait until the installation is complete and it is done.

That's it, now start the first session for android hello world development.

Gnome goodies: add hardware sensor in panel. add stock indicator in the panel.

Today we will add two more applets to the gnome panel. You might want to look into the past article about gnome applets that were configured before. Okay, let's start by installing an applet that will show hardware temperature.

There is a nice package, psensor and it can be install as easy as

$ sudo apt-get install psensor
$ psensor

So just launch the application from the terminal, then see the screenshot below.



On the left, I have configured three temperature to be plotted. Because hardware in different computer are different, so you can enable plotting for different hardware. On the right, it is the psensor preferences, and I have enabled checkbox for Launch on session startup and Hide window on startup.

Next, we will install a stock applet as a favor for a friend. Because in debian, this is not available and now we will download from ubuntu repository. Point your browser to https://launchpad.net/~ce3a/+archive/ubuntu/indicator-stocks/+packages and download latest version of indicator-stocks. As of this writing, I'm installing indicator-stocks_0.2.4-0ubuntu1_amd64

user@localhost:~/Desktop$ sudo dpkg -i indicator-stocks_0.2.4-0ubuntu1_amd64.deb 
Selecting previously unselected package indicator-stocks.
(Reading database ... 321688 files and directories currently installed.)
Preparing to unpack indicator-stocks_0.2.4-0ubuntu1_amd64.deb ...
Unpacking indicator-stocks (0.2.4-0ubuntu1) ...
dpkg: dependency problems prevent configuration of indicator-stocks:
 indicator-stocks depends on libappindicator0.1-cil; however:
  Package libappindicator0.1-cil is not installed.

dpkg: error processing package indicator-stocks (--install):
 dependency problems - leaving unconfigured
Processing triggers for gnome-menus (3.13.3-2) ...
Processing triggers for mime-support (3.57) ...
Processing triggers for desktop-file-utils (0.22-1) ...
Processing triggers for hicolor-icon-theme (0.13-1) ...
Errors were encountered while processing:
 indicator-stocks

As you can read above, there is a dependency problem during installing indicator-stocks. So just use apt-get install for the remaining package. It should be simple process to resolved that using apt. So it is finally installed, check the screenshot below. You can configured a few symbols, it is from finance.yahoo.com.



That's it, from the past and in this articles, I hope your desktop should present as much information as possible.

Gnome goodies: common keyboard shortcut. Remembering state of num lock.

If you have been using linux and there is a key on your keyboard with windows logo, it is known as Super key. This super key will be widely used in gnome 3. Today, we will learn some of the commonly used keyboard shortcut. You can also find other keyboard shortcut in gnome-control-center keyboard shortcut.

Keyboard Shortcut	Description
Super+Up	Maximize window
Super+Down	Unmaximaze window
Super+Left Arrow	Fill half to the left side of the screen
Super+Right Arrow	Fill half to the right side of the screen
Super+click then move	Move window anywhere on screen
Super+m	To bring up a message tray at the bottom of the screen.
alt+tab	switch between applications
alt+`	switch through window of current applications.
super	bring up a new apperance known as activities overview
drag application to dash	this is to add an application which you used often to the dash so you can easily accessed.
drop application to grid	remove application from dash by dragging from dash and then drop into the grid
ctrl+alt+up arrow	switch to the workspace above
type in a file window	To quickly search for file in the file windows.
alt+PrintScn	take a screenshot of the current window only.
shift+PrintScn	select a specific area of the screen.

Not sure why each time of operating system reboot, the state of num lock on keyboard get forgotten. This is really quite puzzling considering gnome has been evolve for so many cycle. But that's okay, we will learn to configure gnome so that it will remember the state of num lock between system boot. Let's launch dconf-editor and expand in the tree in such path. org -> gnome -> settings-daemon -> peripherals -> keyboard. Check remember-numlock-state and check the screenshot below.



With this article, I hope you navigate better in gnome-shell environment.