Linux and Remote Desktop

Recently we've installed a remote server in North America. In order to set up some Windows boxes, we figured it would be easier to download the DVD images from the servers themselves. This posed a problem however, for several reasons:

1. XenServer requires that any Linux installs be specially compiled for Xen. This is due to the way that the Xen guys wrote the code for the HyperVisor. From my understanding (and without going through the lkml) the code was not very 'clean' and/or did not conform to the kernel coding guidelines. This resulted in the Xen code not being available in the standard kernel that comes with most distributions.

2. Figuring out how to add an ISO repository and actually have its contents come up when installing a new VM is harder than it probably should be on Xen. When trying to figure this out, I found plenty of examples of how to add a new iSCSI/CIFS repository to the XenServer, but nothing on how to set up an ISO repository on the local storage.

3. Apparently there's also a way of uploading a Windows XP VM, but this was more complicated to get going than adding the local ISO repository.

Due to these problems it was decided to take one of the existing distributions (Debian Lenny) and install a desktop environment and enable Remote Desktop functionality through the use of one of the below listed technologies. After pissing about for two/three days with these protocols I can honestly say that the NX protocol and the binaries available off the NoMachine site are the easiest to configure and the best working solutions. This is kind of disappointing for me, since I would have loved to see a FLOSS solution out do a propriatary one, but as a programmer you have to give credit where credit is due.

When it comes to Remote Desktop functionality for Linux, there are a few options regarding protocols:

* XDMCP - Basically the original X idea of remote displays hooked up to a mainframe. Couldn't get it to work for the life of me. Also, found a known, unfixed bug whereby enabling remote login makes the gdm listen only to IPv6 addresses
* VNC - Hard to set up and slow
* RDP - See VNC
* NX (FreeNX) - Awesome. Although FreeNX is a real bastard to set up

UPDATE: Found out that Google released their own NX Server called Neatx.

Zend CE Server on CentOS

I just finished installing Zend Server Community Edition on CentOS. One of the problems encountered along the way was that starting Apache would give an error saying that it did not have the necessary permissions to access '/usr/local/zend/lib/apache2/libphp5.so'. This is due to SELinux not allowing the httpd process access to this file. After searching around for a solution, I found that most of the forum posts gave the advice to either switch SELinux to permissive mode or to disable it altogether. To me, this was a bit like throwing the baby out with the bathwater, so after reading up a bit on SELinux, I figured an easier (and more secure) solution was to just add this file to the 'httpd_modules' context. So, here your are:

chcon -t httpd_modules_t /usr/local/zend/lib/apache2/libphp5.so

This command adds the Zend php binary to the 'httpd_modules' context, allowing Apache to load it and start up normally.

MySQL Bug #11918

In the software industry, every now and then you come accross some indescribably dense acts of stupidity that cost you hours of debugging time. When it's not your own code that's the problem, you get to rant about it on your blog ;)

Today I spent the last four hours trying to create a MySQL stored procedure to do something which I thought was quite basic. It just had to take an integer as input and return that number of rows from a specific table and at the end delete the rows. Kind of like a stack data structure (the rows 'pop' out), but with a database. So I sat down and wrote this code:

DELIMITER $$

DROP PROCEDURE IF EXISTS `test`.`testGet`$$
CREATE PROCEDURE `test`.`testGet` (IN numRecords INT)
BEGIN
CREATE TEMPORARY TABLE tmpTable
SELECT * FROM test LIMIT numRecords;

DELETE FROM test WHERE idTest IN (SELECT idTest FROM tmpTable);

SELECT * FROM tmpTable;

DROP TABLE tmpTable;
END$$

DELIMITER ;

So after saving this code and trying to run it I get this cryptic error:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'numRecords;

DELETE FROM test WHERE idTest IN (SELECT idTest FROM tmpTable);

' at line 4 (errno: 1064)


I spent the next two hours trying to figure out what MySQL was complaining about, pulling my hair out, trying to see which part of the code was screwing up.... finally after much googling, I came across this bug report on the MySQL bug tracker, the title of which simply reads "SP does not accept variables in LIMIT clause". The bug's been sitting in the bug tracker since the 13th of July 2005, FOUR YEARS this last July. The bug report is full of comments with detailed workarounds, most of which end up being versions of the 'EXECUTE STMT USING' statement. There's a big discussion in the comments as to whether this is a bug fix or a feature request, meanwhile Oracle and SQL Server continue to dominate the marketplace. Nice going guys. I'm stupified that this bug has been hanging around for four years and is still not fixed. I'm tempted to download the source and have a look at how difficult it would be to patch.

Eclipse Opening Tutorial woes

I've been looking around for a good all around development environment for a while now and today I've decided to give Eclipse a go. I've installed the eclipse package from the Ubuntu 9.04 repositories and everything seemed to be working well. I was a little disappointed with the fact that the Ubuntu repositories only had version 3.2 of Eclipse, when the main stable release was at 3.5, but this didn't bother me too much.I opened up Eclipse and decided to have a go at the first two tutorials, hoping to get an idea of what this IDE's all about.

The first tutorial goes through the process of creating a Java project with the ambitious aim of printing out 'Hello World!' to the command line. Going through the tutorial was quite straight forward, teaching you how to create a new jave project and add classes to the project.

The second tutorial was the same as the first, except that instead of printing 'Hello World!' to the command line you would print it to a window. In order to do this you use the SWT by downloading the Eclipse project and making it a part of your projects runtime. The tutorial went fine until it came to running the code and I ran into the following error:

Exception in thread "main" java.lang.UnsatisfiedLinkError: no swt-gtk-3550 or swt-gtk in swt.library.path, java.library.path or the jar file
at org.eclipse.swt.internal.Library.loadLibrary(Unknown Source)
at org.eclipse.swt.internal.Library.loadLibrary(Unknown Source)
at org.eclipse.swt.internal.C.(Unknown Source)
...

This is extremely disappointing. I mean, this is meant to be the second tutorial that the user works through, it should be bullet proof. The entry barrier to getting up and running on Eclipse should not be so high, that you have to go out of your way to learn the intricacies of SWT. So far, not a very good start for Eclipse.

Update: Got the second tutorial working. Instead of adding the SWT project off of the official site, I added the 'swt-gtk.jar' library found under /usr/lib/java on my Ubuntu install. Still not too happy about having to go to these kinds of lengths to get the first couple of examples up and running, but at least I'm learning :)

Don't write a single line of code without a Specification

Today I was updating one of our servers and naturally had a lot of free time while I waited for everything to download and install, so I started reading the 12 Steps to Better Code (also known as the Joel Test) article on the joelonsoftware blog.

The article makes some really good points about software development and how to do it right. From a programmers perspective it also gives you clues as to what to look for in a company you're potentially going to be working for.

After reading through the article I clicked on one of the links and found myself reading the full 4-part series about functional specifications. This article went into much more depth than the original 12 Steps to Better Code. The articles talked about why you need a spec, how to write a spec, who should write one and some general tips. This series of articles was timely for me personally due to our company having hired a new contractor which has taken on a project that's been dragging on for years at the company and as one of the first things he did was to write a functional specification and a technical specification (although the functional spec is actually referred to as the functional requirements, po-ta-to poh-ta-to). The amazing thing is that this first, relatively simple step has impressed the hell out of management. Finally they have a document that they can refer to to see the full functionality of the finished product and can start answering questions by clients as to what new features the program will have etc... They also look at the document and can get some more concrete idea of which stage the project is at, although this isn't the idea behind functional specifications. The other point that really hit home for me was about how by putting the functional and technical specifications in their respective documents, you minimize the interruptions to your own work, because instead of having management, marketing, Q&A people etc... bothering you with questions all day about how each part of the finished product will work, you can just refer them to the document. I would love it if I could answer all of the annoying questions I get throughout the day with "Have you read the spec?".

Overall, the message of "don't write a single line of code until you have a spec" is a powerful one, now if only I had the self-discipline to stick to it :)

Installing 64-bit Adobe Flash on Ubuntu

Adobe Labs released their alpha flash player 10 for 64-bit linux in November 2008. In order to install it, simply go to the download site, download the .tar.gz file and extract it. The uncompressed file is just the libflashplayer.so. In the install instructions they say to place this file in ~/.mozilla/plugins and restart Firefox. However, when I tried this I found it didn't work. In order to make the plugin load, I placed it under /usr/lib/mozilla/plugins/ and this did the trick.

While most advice recommends that you install the 32-bit version of flash along with an emulation layer, I've found the 64-bit version of the flash player works better than the 32-bit version and is generally quite stable.

Folding@Home

I've recently joined the folding@home project under the name srkiNZ84. Folding@Home is a hugely distributed computing project with the purpose of doing protein folding (anyone remember seti@home?). I've joined TeamUbuntu and started crunching my way through those work units.

At first what got me intrigued with this project was just trying to benchmark my computer(s), but now what really keeps me interested in it is the competition. You see, with this project you get to keep statistics on how many work units you've completed, in what kind of time frame etc... and every member of the project is ranked. This gives rise to cool personal and team statistics screens like this one from extremeoverclocking or this one from xtreme cpu. Personally I think the competition is one of the main reasons that the project has so many followers.

Right now I'm ranked 455th in my team and 171,330th overall. This isn't too bad considering I've only started. However, the only real way I'm going to get into the top 10% or so of the rankings is by making use of a high performance GPU client. These are versions of the folding@home software that run on your graphics card and make use of it's parallel processing capabilities to complete work units in a much shorter space of time. ATI were the first to produce a client for their line of graphics cards, but were soon followed by nvidia, which blew them away with their much better CUDA performance. I'm not even sure that there is a GPU client for Linux (at least not on the official folding@home website), but I haven't been through the whole recruitment post on ubuntu forums, so I'm hoping there's some clues on there.