Archive for category General

ElasticSearch issues upgrading from Ubuntu 15.04 -> 15.10

For some bizarre reason when we did an upgrade from ubuntu 15.04 to 15.10 and elasticsearch was updated from v1.4.5 to v1.6.2 elasticsearch would not start (although systemctl thought it had each time).

Immediately after the upgrade, we received error messages from our application saying it could not connect to elasticsearch.

Sure enough trying to connect to the elasticsearch service failed when we attempted to use curl -XGET 'localhost:9200'

Another strange thing is that systemctl says that elasticsearch is running perfectly, even though the process is not running when we execute ps -aux | grep elastic …

It turns out the file had been deleted in the upgrade and the elasticsearch user could not create a new one.

touch /var/run/
chown elasticsearch /var/run/

However, that is not all, I started receiving a new and exciting error message (see stack trace below). Read the rest of this entry »


Nasty Class loader issue: “java.lang.LinkageError: loader constraint violation: loader previously initiated loading for a different type…”


First a bit of background, I am working as part of a team responsible for building a bespoke content management system for educational uses and the back end uses the following technologies:

  • Java Tomcat 7.0 server
  • Rest Easy 3.0.6.Final
  • ElasticSearch 1.0.1
  • Google Guice 3.0 for dependency injection
  • Eclipse Kepler Build 20130919-0819
  • Counterclockwise (Clojure plugin For Eclipse) 0.20.0 & 0.24.1.STABLE001 – This becomes important later even though I am not using it really.

The problem

Now to describe the problem. For some reason after integrating ElasticSearch with our project a nasty error as seen below started happening (and breaking the whole site at runtime when running within eclipse):

SEVERE: Servlet.service() for servlet [jsp] in context with path [/rutherford-server] threw exception [Filter execution threw an exception] with root cause
java.lang.LinkageError: loader constraint violation: loader (instance of org/apache/catalina/loader/WebappClassLoader) previously initiated loading for a different type with name "javax/servlet/http/HttpSession"

This problem seemed to refer at a random place in our code in the stack trace. This random place had previously worked (and is totally unrelated to the Elastic Search stuff I was working on) in my case it occurred in a User Manager class that deals with sessions (hence the reference to HttpSession). The elastic search stuff didn’t have anything to do with the user manager or even use the HttpSession class as far as I was aware but seemed to trigger the error when the code for the elasticsearch java api was inserted.
Read the rest of this entry »

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Dual Booting: Installing Windows XP after Windows 7 – Nightmare Solved

After spending 3 hours trying to get my PC which was preinstalled with Windows 7 to dual boot with XP, I finally found the solution that worked for me.

I tried all of the suggestions that were given in the support forums including meddling with my BIOS and none of them worked for me. I even tried using different partitioning software because I was worried the partition wasn’t setup properly. – It didn’t make a difference.

My Solution:

  1. I used Windows 7 partition manager to create a new primary partition to house my new Windows XP installation. I set it to FAT32 file system just for simplicity and because I had started to stress out with NTFS at this point.
  2. Then I put my windows XP disc in and began the installation process, however the problem came when the computer finished the command line based installation and was ready to move into the Graphical Interface section of the install process. When the system rebooted it would halt with a message “Error Loading Operating System”. Which was very unhelpful.
    Restoring Windows 7 to Working Order
  3. In order to get back to a reusable Windows 7 Installation you have to replace your Windows XP CD with your windows 7 DVD and reboot from the DVD.
  4. After selecting your language, click on the little link in the left hand side of the screen and select the command line from the list of options (after you select the Windows 7 installation you want to repair).
  5. In the command line if you run the following commands in order;
    bootrec /FixBoot
    bootrec /FixMbr
    This should allow you to boot back into your original Windows 7 installation.
    Completing Windows XP Installation
  6. Now once you are in windows 7 we have to find a way of getting the bootloader to give us the option to boot into the incomplete installation of Windows XP Service Pack 2.
  7. Fortunately a handy freeware application exists which makes this relatively easy. EasyBCD.
    Screenshot of EasyBCD

    Screenshot of EasyBCD

  8. Install this application and then click the Add/Remove button, then add a new Windows XP menu item. After you have added it you may need to go to configure the XP menu item to use the correct drive letter. I did.
    Final Steps to Success
  9. Now this is where the secret comes in, if you were to try and just reboot now and select the windows XP partition from the boot loader it would say there is no windows XP boot loader yet and the whole thing just wont work.
  10. What I did was nip over to my laptop and copy across the essential files from my laptops windows XP installation to enable the other installation to boot and complete. Copy and paste these into the root of your incomplete windows installation (and then magic! you can use the boot loader to go and complete your windows XP installation) So far it all works correctly after that! Woo hoo!

To be helpful I have attached a copy of the files I copied and pasted from my laptops windows XP installation that were required to complete installation of windows XP on my new partition. I suggest you paste them in from windows 7 when you have completed the first stage of the installation and rebuilt the MBR.

Boot Files Zip File: windowsBootFiles

Subdirectory windows (which represents the root of the windows partition file system – these files should be copied and pasted directly on to the root drive of your new windows XP partition NOT the windows directory which will have already been created by the XP install CD)

– boot.ini
– ntldr (the most important file)

The zip file here contains the boot files without the pagefile.sys and hibernation files as I didnt think these would be necessary and were quite big.

Hope this helps!


Eclipse Plugin Development: Wrapping Text In a Label

Today I was having trouble wrapping text in a label on an SWT shell in an eclipse plugin.

I found a useful guide that explains what was going wrong. It can be found here.

Wrapping Text Guide

The problem was I hadn’t defined a widthHint for the grid data object. This is apparently used by the label component to work out whether it needs to wrap or not.

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SSH Port Forwarding Guide

This is a good Guide. for setting up port forwarding with putty and squid.

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Hello world – My first post

I am currently a PhD Candidate studying Technology Enhanced Learning at Durham University. Have a little look at my website for more info.

More specifically I am looking at folksonomies and programming to see if there are any applications that could be used to improve undergraduate programming courses.

I have started this blog to help other coders who are programming on similiar things to me. Primarily, for things that I had problems with or got frustrated with, when I couldnt find help online or on irc.

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