GizmoLA.com - Tech

Get files from subversion without creating a sandbox using svn export

nospam@example.com (David Rolston) — Mon, 22 Feb 2010 23:27:59 -0800

One of the first things people learn about using subversion is how to do a "checkout" using svn co. The svn checkout command pulls files from the subversion repository into your "sandbox" and in so doing creates what subversion calls a "working copy". A working copy includes a .svn directory in every subdirectory of the working copy, which is chock full of directories and files that svn uses to determine what you're doing in your sandbox.

A "working copy" is designed to be just that -- a copy of the source tree built with the assumption that you will be making changes and committing them back to subversion. But what do you do if you want the files, but you don't need or want a sandbox?

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Finding "Next Monday" using MySQL Dates

nospam@example.com (David Rolston) — Tue, 01 Dec 2009 22:18:39 -0800

Several people who read my article on Exploring Mysql CURDATE and NOW. The same but different posed questions regarding how to return a valid MySQL date equivalent to "Next Monday" given any particular day, as determined by MySQL's CURDATE(). This is a little bit tricky, but can be done entirely in MySQL syntax, making it usable with Calendar applications built on top of MySQL queries, without the need to use serverside date functions. This builds upon concepts discussed in my prior article, so if you have trouble understanding the implications of using CURDATE or DATE_ADD, you should probably take a minute and read that article.
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Centos Virtual LAMP server -- Part II

nospam@example.com (David Rolston) — Tue, 04 Aug 2009 18:10:08 -0700

*Part 1 of this series is here*

Customizing your LAMP server

Unix people are probably familiar with the father of the DNS system -- the /etc/hosts file. The hosts file has a simple format:

ipaddress hostname

In the days prior to DNS, people would update a master hosts file and copy it around to all the servers in the enterprise. Surprisingly Windows versions also support this file, as a way of overriding DNS, so we can use this to our advantage, by adding an entry for our development server. In this example, I'm going to use dev.gizmola.com, which is not a real server.

One important reason to do this is that Apache and other web servers, use a feature of HTTP 1.1 that specifies a header field named "Host:". This mechanism facilitates the service of multiple domains from a single apache server, through the configuration of apache virtual host (or vhost) entires. The server uses the Host name in the HTTP header to determine how to route requests, so without host name resolution. you have to use non-standard ports and other mechanisms that are more trouble than they're worth. a

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Intel's T6500 -- No VT for you! Sony: You got Vaio VT? We turn it off.

nospam@example.com (David Rolston) — Thu, 30 Jul 2009 14:48:49 -0700

At the time I'm writing this, you can easily find websites still listing the specifications for Intel's T6500 chip as including Intel VT. The T6500 is prevalent in the consumer Notebook space particularly because it was built to work with an 800mhz front side bus, allowing it to go in cheaper motherboards. You'll find the T6500 in a lot of midrange and budget 64bit notebook computers, from nearly all the major notebook manufacturers. Whether or not you care about VT depends on your interest in 64bit Virtualization software from Parallels to VMWare to Sun Virtualbox to Xen to VirtualPC.

VT is a marketing name for the hardware assisted virtualization workaround, originally named Vanderpool, that adds the Virtual Machine Extensions (VMX) instructions needed by VM's like Xen and Sun VirtualBox to provide 64bit OS virtualization. AMD has a similar set of extensions it added, marketed as AMD-V, although they built in the memory segmentation support that alleviates the problem with 64bit memory virtualization as far back as the D revisions of their AMD64 chips. One such website includes this boilerplate--

T6500 contain Advanced Technologies about Intel Virtualization Technology that increasing manageability, security, and flexibility in IT environments, virtualization technologies like hardware-assisted Intel Virtualization Technology (Intel® VT)

Click to see full size screenshot of original Intel specification.

If you were to have visited Intel's own site prior to July 20th of 2009, you would have found information indicating that the chip had VT support. This is a fairly mind boggling omission when you consider that the chip was manufactured, delivered to customers, and has been sold to customers for well over a month before Intel corrected its own site! On July 21st, Intel updated its website, and VT support is now removed from the specs. An Intel representative agreed that the information on the site was incorrect, once challenged by a consumer with a T6500 based machine, who had used Intel's own tools to enumerate the features on the chip.

I am sorry, I was mistaken. Thanks for bringing this to my attention.

The T6500 does not support VT. I used ark.intel.com as my reference, but as you pointed out, the information turned out to be incorrect. The processor feature information for the T6500 contained within ark.intel.com has been corrected. VT is actually not a feature of the T6500.

The processor identification tool is correctly reporting that VT is not a supported feature of the Intel® Core2 Duo Processor T6500.

John S.
Intel Customer Support

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Run a Centos Lamp development server on XP, Vista or Win 7 using VirtualBox

nospam@example.com (David Rolston) — Thu, 16 Jul 2009 14:07:21 -0700

If you use a Windows based workstation or notebook computer virtualization offers a way for you to run a linux server environment using the same linux distribution and configuration you'll use in production. Virtualization allows you to explore clustering and network setups that can't be tested on your workstation alone and simplifies your development environment by keeping the LAMP environment contained inside a VM.

While VMWare offers these capabilities with their VMWare workstation product, Sun has created a free alternative called VirtualBox, with many of the same capabilities in VMWare workstation. VirtualBox runs on a variety of intel chip based operating systems including OS/X, Windows XP & Vista, Linux and Solaris, and supports the installation of many different "Guest" operating systems. In this article, I'll detail the installation and configuration of Centos. Centos is a great choice for a Linux server operating system, as it is widely used by hosting companies due to its Redhat Enterprise Linux (RHEL) core.

Our goals in this setup will be:

• Centos server running the LAMP stack
• XP can be used to develop code using the IDE of your choice.
• The XP Workstation can communicate with the linux server using standard tools: putty, winscp, firefox
• The setup works even when no other networking is available. When a network is available, no network reconfiguration is required.
• Use XP to setup private domain resolution so apache vhost configurations can be tested.

Let's get started.

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Too much information about the MySQL TIMESTAMP

nospam@example.com (David Rolston) — Thu, 23 Apr 2009 13:55:47 -0700

The MySQL timestamp is an oddity, being both a mySQL "Data Type" as well as a type of specialty column that provides a built in default. It doesn't help matters, that the timestamp was changed significantly around mysql version 4.1.

The Old TIMESTAMP

In older mysql versions, the TIMESTAMP was not in the same format as a DateTime column, and you could also set up truncation by defining the TIMESTAMP to have a fixed size. For example, you could define a TIMESTAMP column to be a TIMESTAMP(4) which would then only store the 4 digit Year portion of a DateTime value. I won't go into much detail on the pre version 4.1 TIMESTAMP, however, if you're stuck with an older version of MySQL I recommend you read the manual carefully before you attempt to use any of the information here. I'm going to concentrate on the current TIMESTAMP.

TIMESTAMP Properties

At its most fundamental, the TIMESTAMP is really nothing more than a Unix TimeStamp, which is to say, that internally it is stored as an integer value of seconds. Where a MySQL DATETIME column can be used to store any date and time from Jan 1, 1000 to 12/31/9999, the TIMESTAMP is limited in the same ways that the Unix timestamp is currently limited -- it can only store values from Jan 1, 1970 to Jan 9, 2038.

Those familiar with Unix design, will recognize the Jan 9, 2038 date as being the next big "Y2K" computing panic, and if you're young enough, you may realize a large payday in your future, selling remediation services to companies in roughly another 28 years. The folks at http://www.y2038.com/ are already estimating this to be as much as a 10 trillion dollar jackpot, although no doubt by that time most of the coding will be done by the Morlocks from their underground cave cities. Outsourcing of IT to Morlocks will be a major industry trend by the year 2020, mark my words.

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Mysql Update: Null + 1 is Null!

nospam@example.com (David Rolston) — Thu, 12 Feb 2009 12:18:11 -0800

You can't add to Null

Here's something about mysql create table definitions that can easily catch you if you aren't careful. Consider this table definition:

CREATE TABLE screenshots (id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, votes INT);

mysql> CREATE TABLE screenshots (id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, votes INT);
Query OK, 0 rows affected (0.09 sec)

What the user wanted was a simple table to keep track of user submitted screen shots. Of course the real table had a submission date, and name column but I've omitted those in order to focus on what can happen when you allow a numeric column to have NULL values.

In the application in question, when a user votes for the screen shot they like, the system should "count" the vote, by increasing the values in the "votes" column by one. Initially the developer working on this application was trying to read the value from the database, and in a PHP web script, they would increment this value and take the result and set "votes" to be equal to it in an UPDATE statement. I explained that this could cause lost votes, because if two or more users were voting at nearly the same time, each would overwrite the value of the "vote" column. In fact there are scenarios far worse than that --- a user with a cached page could vote and set the vote count back days or weeks. I didn't bother to mention the possibility that someone might recognize what was going on in the web form, and start tampering with it, since it was plainly evident that the form was passing the current number of votes.

One of the many benefits of using a relational database is built in concurrency. In an UPDATE statement, you can add to the value of the column without having to know what its original value is, just as computer languages allow assignment to a variable that references the variable's current value (ie. $a = $a + 1, $a++).

UPDATE screenshots SET votes = votes + 1 WHERE id =

All that's needed is to have the serverside language provide a value for a particular "id" and the votes will be tallied and updated correctly. Even more importantly, mysql will serialize the updates, insuring that no votes are lost.

However, given the original Mysql CREATE TABLE statement , what will happen if our code embeds the UPDATE statement provided?
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Lampsig 2008 Presentation on Subversion for Lamp Developers

nospam@example.com (David Rolston) — Mon, 13 Oct 2008 14:24:39 -0700

Here are the slides for the presentation on subversion I gave at the September 2008 LampSIG meeting. I hope some may find them useful, however they were meant only to provide a skeleton for the talk, and aren't a complete tutorial by any means. The following links to other sites were mentioned in the talk:

The Red bean book, aka Subversion manual
The svnmerge python script
Subversion tips Article
Subversion Cheat Card

Linux shell scripting: bad interpreter: No such file or directory

nospam@example.com (David Rolston) — Mon, 15 Sep 2008 16:22:39 -0700

This error pops up for a couple of reasons. At the top of the script there will probably be a line that looks like this:

#!/bin/sh

This is telling Linux that this script should be interpreted using the /bin/sh program. So your first step is to verify that program exists. I tend to use:

which sh

This will typically come back with a response like this:

/bin/sh

This is telling us that the path to the sh program is in fact /bin/sh, matching the path specified at the top of the script. Ok, so what gives? Well, it's possible that this script was made on an operating system that has line ending characters different than linux. This could have been on on a Mac or PC, or the file could have been converted when it was packaged. In this case, you get the relatively misleading bad interpreter: No such file or directory message, which is really trying to look for sh, although you don't get any indication of the fact.

So, how to fix? Read on.
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New Lula/Lampsig Coop Server

nospam@example.com (David Rolston) — Thu, 24 Jul 2008 10:55:09 -0700

So the UML Coop has finally after 3 years of talking about it, acquired a new server from Silicon Mechanics. Read the rest of the article for the complete specifications. We will be moving off User Mode Linux (UML) and on to OpenVZ. This change will allow us to accept some new members to the coop, so if you're interested drop me a line.

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AT+T Wireless XPress Mail Courier IMAP setup problem - Trash Folder?

nospam@example.com (David Rolston) — Sat, 12 Jul 2008 14:40:17 -0700

Having recently left a company that had Exchange, the removal of Goodlink from my Samsung Blackjack left the phone in a fairly broken state. I fixed this by doing a full reset (Turn on phone while holding Up Arrow) and choosing 1. This put things back in basic working order.

My efforts to use the built in email client to access my Courier IMap Email had never been successful, so I decided to explore AT+T's XPress Mail system. This consists of client software you install on the phone, and a desktop application that connects through AT+T's servers to give you access to your email remotely, and also can be used to give you access to files on your PC.

Upon install of the client you choose your mail server (in my case IMAP) and input the basic settings required by most IMAP client softare (Account name & Password, email address, the IMAP server, SMTP server, security settings, etc). I did notice an unusual configuration box asking for "Root Folder Path" which I left blank. Here's where the fun began.

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LAMP Tutorial Series originally published on PHPFreaks.com

nospam@example.com (David Rolston) — Tue, 27 May 2008 12:52:58 -0700

A few years ago I published a 3 part LAMP tutorial series entitled LAMP, MySQL/PHP Database Driven Websites on the well known php community website PHPFreaks.com. This series dealt with a slew of practical issues including how a LAMP server works, relational database design using MySQL, many to many tables, SQL inner and outer joins, practical PHP debugging, php documentation tools, basic PHP classes, css, interactive javascript & DHTML with a chooser widget, php HEREDOC and php basics like how to process forms and utilize GET and POST methods.

The series was fairly successful, (a 4.5 of 5 after hundreds of ratings), many pages of comments and questions, and page views to the 100k's+ although PHPFreaks auditing system was turned off at some point and stopped recording views.

Unfortunately, some years ago PHPFreaks.com suffered some fairly catastrophic issues with its publishing system. There were also some bugs, and the site was exploited with some XSS, and the admins simply decommissioned the majority of the site. My series was part of what disappeared. At that point, a couple of college Computer Science courses on web development had taken the series and integrated it into their curriculum, and the professor of one of these courses had converted it into a Word document, which I was able to download and convert to pdf.

I plan to write a compatible publishing addon for gizmola.com so that I can take the original markup and republish it here, but in the meantime, here is the series in pdf format. The conversion utility they used stripped out the original markup, and page breaks are gone, but the text, source code, and illustrations are all still there.

I also offer all the source code for parts 2 & 3 of the series. I'm not sure what happened to the source for part 1, however, it is all included inline in the tutorial. The LAMP, MySQL/PHP Database Driven Websites series is now available in pdf format. Click here.

Free Apple Mac style Dock with Windows Vista and RocketDock

nospam@example.com (David Rolston) — Sun, 10 Feb 2008 14:32:25 -0800

One of the distinctive features of Apple computers is a piece of software called "The Dock". The Dock is sort of an always there menu with big icons that spawn your most frequently used programs. Docks also can run small programs or docklets that can do things like display a clock or show you the weather. Docks also can be configured to display running programs that have been minimized in a mini window. You bring a running program to the front, or launch a program by hovering over the dock with your mouse, and clicking on the icon.

I suppose that people who don't know any better might think that this is something you can only get from Apple, but as it turns out there are docks for Linux and Windows. At home I have a Gateway computer running Windows Vista business, and I wanted to add a Dock. After a bit of hunting, I found some recommendations and settled upon RocketDock from Punk Labs. Punk Labs as it turns out is really a couple (he's a programmer, she's a designer) who go by the pseudonyms of PolyVector and Skunkie respectively. The about screen describes RocketDock tongue in cheek as a "peace offering" from the pair of self admitted Apple fans to Windows users everywhere.

The RocketDock website provides links to the various versions and a straightforward online manual. You get most of the features of the Apple Dock program, and it's very easy to work with. Once installed and running, the RocketDock appears at the top of the screen, with a set of default icons. Right click on the RocketDock and you get a menu that lets you adjust Dock settings. There are various themes that will style the look and feel of the RocketDock, and the RocketDock site offers an Extra's link with downloads to styles and docklet programs other people have contributed. While it's just a quibble with this otherwise great program, there's not much in the way of Docklets available, but I found it hard to resist adding on the simple analog style clock.
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Fun with Windows Vista and the Maxtor Shared Storage Drive

nospam@example.com (David Rolston) — Fri, 27 Jul 2007 23:48:49 -0700

I have a pair of 200 gigabyte Maxtor Shared Storage drives -- which are relatively inexpensive network storage drives that integrate with windows client machines. They come with an ethernet port you use to connect to a switch or hub on your home LAN, and will plug and play by negotiating an IP via DHCP. Maxtor (now owned by Seagate) provided a windows client that helps with finding and setting up the drives, since they advertise themselves as Workgroup peers that can be shared. I use the drives to store things like digital camera pictures and DVD's I've ripped in order to play them through my Tivo Series 2. They also come with some software that makes it easy to backup the My Documents area of our windows machines.

With Windows XP, the Shared Storage drives worked fairly reliably, but after I upgraded my Gateway desktop to Vista Business edition, I found myself unable to connect to the drives I'd mapped to it. Trying to mount them manually, I'd receive a login dialog. The name and password I use from my XP Pro based computer works fine, but on Vista the drive would reject the same credentials.

It took me a while to sit down and dig into the issue, and my first guess was that firmware might fix the problem. The Shared Storage drive predates Vista, so it wasn't a total surprise to me that authentication didn't work. The bundled web interface allows you to login with a browser, and administer the drive, setting up user accounts and mounting and unmounting USB devices you can connect to either of 2 provided USB ports. We have a printer attached.

After logging into the webserver, it displays a menu that includes the Firmware version -- mine was 1.2. A quick search of the Seagate site, and I found Maxtor offering version 2.6.2 firmware! The Advanced Settings | System Maintenance menu | System update menu provided a simple upload and update process that was completed in about 2 minutes. Despite the major point upgrade to the drive bios, I still was unable to login to the drive from Vista. What made this even more confusing is that I somehow had been able to successfully find the unit on the Windows network, authenticate to it and map a drive when I had first done the Vista upgrade. A bit of googling on the problem, and I discovered something surprising about the Maxtor unit I'd never suspected -- it is actually a linux box....
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Xen 3.0 Fedora Core, RHEL, Centos 4.x How-to

nospam@example.com (David Rolston) — Tue, 12 Jun 2007 00:28:03 -0700

I gave a talk on the use of Xen for web developers at Lampsig. It took me a while to get my notes transcribed, but here at last they are. This prescription has been used by me to install Xen successfully on a Fedora core 4 box, Centos 4.3 and 4.4 boxes, and should probably work on RHEL, assuming you can figure out how to get the packages you need.

I cover use of file backed file systems, and how to mount and edit them, as well as expanding a file based filesystem.

I have run gentoo and Centos guests I got from jailtime.org and have found them to be very stable. I even was able to use this on a 64 bit server, although I did have to build my own guest. Many people who have had trouble getting Xen to work reliably when using the packaged (rpm) versions of Xen may find this prescription fixes their problems.

Xen 3.0 Centos How-to