Padd Solutions

When I was setting up my server, I was faced with the problem of configuring subdomains to work with a dynamic DNS service such as DynDNS or No-IP. I recently had a user on the Ubuntu Forums ask me how I ended up getting things to work, so I wrote this article to explain.

The first step is to configure settings with your dynamic DNS service. The following instructions are for No-IP, but they should be very similar to other services such as DynDNS:

1. Navigate to the settings page for your domain.
    
2. Find the "Enable wildcards" option and enable it. This directs all domain requests, no matter the subdomain, to Apache. Here is a picture for No-IP:

After configuring your provider, next we need to configure Apache. In order to direct to the right location on the server, you need to configure Apache to know where each subdomain should be directed.

1. On your server, navigate to /etc/apache2/sites-available. This path is for Ubuntu, you will probably need to work with httpd.conf on other systems. This is where Apache gets information about sites and subdomains on Ubuntu.
    
2. If you have not already done so already, create a new .conf file. Although you can name it whatevery you want, it is useful to name it with the format, [yourdomain.com].conf. This file will be used instead of default because it is easer (for me at least) to start from scratch for something like this.
    
3. Open up the file, and add the following lines:

   <VirtualHost *>
   DocumentRoot /var/web/www
   </VirtualHost>

   This is the main entry, it directs all of the undefined subdomains (which we will define later - be patient) to /var/web/www. Of course, you will need to add your own configuration like log files; this is just the bare minimum to get you going. The path can be whatever you like. Note that your changes will not be added until step #6, so hang out.
    
4. Now you can define other subdomains and their paths. Here is an example for foo.clustur.com:

   <VirtualHost *>
   ServerName foo.clustur.com
   DocumentRoot /var/web/foo
   </VirtualHost>

   Notice the only difference is the ServerName attribute. You can add as many of these directives as you would like into your .conf file.
    
5. Now we need to enable the settings we just made:

   sudo a2dissite default
   sudo a2ensite [yourdomain.com].conf

   The first line disables the old default configuration file, and the second line enables your new .conf file, whatever you named it.
    
6. Finally, we can restart apache:

   sudo /etc/init.d/apache2 graceful

   Now all of your subdomains should work! If you're stumped or have any suggestions, please feel free to comment - I'll do my best to help you out.

My server used to have a 16GB hard drive, and did not receive regular automated backups. I wanted to upgrade the drive to an 80GB one and use the old drive for automatic backups. This switch required that I somehow move the entire server installation from the old to the new, larger drive. So I decided to use a tool called Clonezilla. I cloned the old drive onto the new drive, and set the new drive to the master. Booting up with the new drive worked fine. I put in the old drive (which still had the server installation) as a slave for backups. It was then that I ran into an interesting problem: no matter what I did, the old drive would always boot instead of the new one. After some probing, I found out that GRUB was run on the new drive, but it always pointed to the old drive. After about 6 hours of banging my head against the wall, I finally figured out that the UUIDs for the two drives were the same since they were cloned. Instead of using the generic (hd0,0), the Ubuntu distribution uses UUIDs by default to point to the drive that should be booted from. The UUIDs were not so universally unique anymore, and GRUB got confused and booted the old drive. So I guess the moral of the story is always make sure you change the UUIDs whenever a cloned drive is used. Anyways, sorry if this notice came too late. I hadn't expected to run into such trouble.

For reference, here's the steps to change a duplicate UUID:

1. Run uuidgen to generate a new UUID.
    
2. Type in tune2fs /dev/hdaX -U [newuuid] to actually update the partition's UUID. Be sure to replace hdaX with the correct partition and [newuuid] with the UUID given by uuidgen.
    
3. Verify that the UUID was changed properly with vol_id /dev/hdaX.

All bundled up, the command is uuidgen | xargs tune2fs /dev/hdaX -U ; vol_id /dev/hdaX. If you just need to clear out the old drive with the duplicate ID, reformatting it would do the trick, too.

If some of you are wondering, this is the source of the recent downtime my server went through. The sites that were affected included this one, and my NXT++ and Linux4nano wikis. The sites were on and off for about a period of 24 hours. I hope this short tutorial helps some people solve the problems I experienced.

So you know how to install Microsoft Office, upgrade drivers, and maybe even do a little overclocking or programming here and there. But have you ever wanted to know more about a computer - how it really works? Here are just a few ways that you can learn a bit more about the mysterious machine.

1. Open up your computer This is a fun, interactive way to learn what's really under the hood. You can learn a lot by opening something up and picking out what the different parts do. Here is a link that explains some of the details. Although opening a computer might be a little intimidating for some people, keep in mind that computer parts are very durable, even if you have a laptop. It's also safe, as long as you unplug it from the wall first! :-)
    
2. Set up a home server with an old computer Pretty much everyone has at least one old piece of crap computer laying around. One of the best uses for a computer like that is to set it up as a home web server. It can teach you a lot about the Internet and also let you host your own site!
    
3. Install Linux This can teach you tons about how a computer boots and what an operating system really does. Installing a Linux distro like Ubuntu is good since everything is open source. Linux also exposes many advanced and low level functionality that Windows and OSX try to build a wall around. By using Linux, you can tinker and examine with parts that are hidden in other operating systems.
    
4. Upgrade your PC components Has your computer gotten too slow to run the latest games or applications, or do you just want a general speed up? Instead of buying a brand new $500 computer, try upgrading individual components like the RAM, graphics card, or CPU. This can be much cheaper, and is not as difficult as you may think.
    
5. Learn a low-level programming language Everything that runs on a computer was written with a programming language. Low-level languages like C and Assembly teach you the most because they are more connected to the computer's memory. C is a great language to learn, but if you really want to understand computers, learn Assembly.
    
6. Do things the 'manual' way In a world of automatic everything, it is nice do do things the manual way every once and a while. Too much automation can cause you to forget what really happens in the background. Try mounting your flash drive manually, or compiling and installing that latest snapshot from source. Who knows? You might end up needing to do these sorts of things manually if something is not working.
    
7. Write a barebones kernel What better way to understand an OS than to make one yourself! Making a simple kernel is not as hard and scary as many people think it is. Of course, if you want to make your kernel able to do something useful, be prepared to do a lot of reading. Here is a great place to start out with OS programming.
    
8. Read a book on digital electronics It's hard to understand a computer if you don't know how different computer parts can communicate with each other. I highly recommend Digital Electronics Demystified, because it teaches you all the essentials. You can also use this knowledge to build some neat circuits.
    
9. Program a microcontroller This requires a light background in electronics, but programming a microcontroller can be fun and useful. You can program microcontrollers in C or Assembly. You can also make a bunch of neat circuits with it, too.
    
10. Read the book 'Code' This is a really great book about how computers really work. You can find a review of it here.