PHPNW is primarily a conference aimed at professionals within the industry to allow them to learn from each other and discover new ideas and techniques which they can then apply to their every day work. What is less prominent is how this is equally as useful for students, who may want to work in this same area once they have graduated.
Virtual Hosts for Development with Apache on Ubuntu
I do a lot of development on Ubuntu, as I often have multiple projects on the go which are nothing to do with each other, it’s often easier to create separate virtual hosts on my local development machine. This means that when they are ready for the “real world”, they are already set up as isolated sites at the root of their domain (rather than in a subdirectory of an existing site).
In order to do this, you need to create a new virtual host in your Apache config. Create a new file in the directory /etc/apache2/sites-available and open it in your favourite editor. It doesn’t matter what the file is called, but it’s best to keep it descriptive. We’ll call this project “mysite”, so the file can be called “mysite”. In the file we need to configure the Apache virtual host.
<VirtualHost 127.0.0.1> ServerName mysite.localhost DocumentRoot /var/www/mysite/public/ </VirtualHost>
In the VirtualHost tag, you put the IP, seeing as I only want this for local loopback (for development) I have just put 127.0.0.1. The ServerName is the URL that you use to connect to the site and the DocumentRoot is where the public documents are stored. This is a very basic set up, so there are many more options you can add.
To make the site enabled, you create a symbolic link to the file from the sites-enabled directory.
cd /etc/apache2/sites-enabled ln -s ../sites-available/mysite mysite
You now need to add the subdomain (mysite.localhost) to the list of hosts, so open /etc/hosts in your favourite editor and append the line:
127.0.0.1 mysite.localhost
And then restart Apache:
sudo /etc/init.d/apache2 restart
Now you should be able to visit http://mysite.localhost on the local machine (assuming the directory does actually exist).
This should also be similar on MacOS and other linux Distros, but the file locations (particularly for Apache) will vary.
LTSP Part 2 – Configuration
In the previous post I had the problem:
… when I boot up, I get the Ubuntu boot screen, which shows it’s connecting to the terminal server, however it then fails with an errror saying
Error: Failed to connect to NBD server
And I get sent to a basic busybox shell.
There were two reasons for this.
PXE… booted
First of all, because I obtain the DHCP separately from the network boot, I need to treat it as if it’s a static IP. LTSP can handle static IPs, but this posed a couple of problems. I would need to specify a separate config file for each MAC address in the pxelinux.cfg/ directory. Secondly it would require each MAC address to be given the same IP each time (this was not going to happen).
So instead of getting gPXE to PXE boot, I completely bypass pxelinux.0 and use my own boot script. In this script I pass in the IP and other information. gPXE has some environment variables which can be used for this, so I wrote a script (The ‘x’s should be replaced by the terminal server’s IP address).
#!gpxe
dhcp net0
kernel tftp://xxx.xxx.xxx.xxx/ltsp/i386/vmlinuz ip=${ip}:xxx.xxx.xxx.xxx:${gateway}:${netmask}:${hostname}:eth0:none nbdroot=xxx.xxx.xxx.xxx:2000
initrd tftp://xxx.xxx.xxx.xxx/ltsp/i386/initrd.img
boot vmlinuz
This script retrieves the kernel, and passes as parameters the environment variables (which were set by the dhcp) the IP, gateway, netmask and hostname. Another parameter is the nbd server location and port. The we retrieve the initial ramdisk (initrd) and boot.
More haste less speed
After that was fixed, on my test machines it still didn’t connect to the NBD server. This is because my test machines are core2duo 3ghz with 4gb RAM; they were so fast at booting up, that it didn’t get a response from the NBD server in time. I diagnosed this by adding the parameter:
break=mount
To the kernel line in the script above. This stopped the boot, then it got a response from the server, and when I pressed ctrl+D (to continue the boot) it booted up fine. This is a bug in the ltsp_nbd script.
I solved this by logging into the terminal server and opening the file /opt/ltsp/i386/usr/share/initramfs-tools/scripts/ltsp_nbd, then added the line:
sleep 5
after the line:
ip link set lo up
This meant that the script paused for 5 seconds to allow the NBD server to respond.
Once edited the initramfs needs updating, as do the kernels:
chroot /opt/ltsp/i386 update-initramfs -u ltsp-update-kernels
I will be writing a part 3 to this sometime soon talking about some of the customisations I will be adding.
LTSP Part 1 – gPXE
Disclaimer: This is a work in progress blog post. There may be better ways of doing things, and things may have been done wrong. Although I hope you will find this helpful, please don’t take the contents of this post as gospel.
At work we have Ubuntu terminal servers which the students currently connect to using NX on ThinStation in the labs. This is not an ideal setup, especially because the ThinStation kernel is too old to run on (even relatively) modern hardware. It is designed to setup an old computer as a thin client, and allow it to access a terminal server which will do all the hard work.
The other issue which we have is that the network is not owned or managed by my department (computer science), but by the central IT department of the university. This means I do not have access to the DHCP server which is required to PXE boot the computers. On top of this, the computers need to dual boot between the thin client/terminal server and a local installation of Windows.
This is where gPXE comes to the rescue! What gPXE allows me to do is retrieve an IP address from the university DHCP server, and then create my own network boot script completely separately.
The Research Begins
As some of you may know, I have now officially started my masters. It is a technical MSc (by Research) on Location-based Social Media Services. The easiest way to describe this is I will be designing and developing a Wiki for a variety of media (text, audio, images and video) which (unlike Wikipedia) is not found using “keywords”, but instead is found based on the location of the client.
I am currently starting a literature survey in this area and have discovered a great, free, multi-platform reference manager called Mendeley, which is incredibly useful for literature storing, organising and tracking (and will even generate a bibliography)! I am researching on who’s currently doing what in location based and social media applications. This includes what applications are out there, what technologies are out there (for information transfer/web services and location analysis) and also what is currently being researched.
I will hopefully be blogging regularly about this, and keep this blog updated with my findings. Please leave comments if you have any suggestions regarding areas I should look into, applications or if you have any insight into this area.