Tim Child

Note: please backup and make sure that you have a copy of your data and virtual images, this can go wrong and I won’t be held responsible. This worked for me, and might not work for you. For ext4 please use the latest GParted.

As I migrated from raw or qcow images, some of the partition sizes that I have to work with are not as big as they could be. So I need to resize.

I generally give some of my hosts a 24Gb LVM virtual group each. But the image files can be as small as 2Gb – A lot of wasted space which the filesystem on the image might as well have. These instructions assume that there are only two partitions, a main partition, and a second Linux swap partition (either on an extended partition or a primary).

First taken the image offline, then get the name of image that you wish to resize, then the disk storage items:

In my case it was “/dev/vdisk05/vm-102-disk-1″. Then you can check to see how large the volume group is set to (vgdisplay) resize:

Next I mount a SystemRescueCD on the CDRom, and make sure its the first item in the boot sequence. Then boot into the system, go for the first choice in SystemRescueCD, and it will give you a rootprompt (I am VNC’ing into the system so that I can access the console as if using a physical machine):

From a command prompt do (check file system, repair, remove journal):

1. fsck -n /dev/sda1
2. e2fsck -f /dev/sda1
3. tune2fs -O ^has_journal /dev/sda1

Then do the following in the GUI:

1. Choose CD > System > GParted
2. Delete the swap partition as it will be the last
3. Resize partition, leaving some space for a new swap partition
4. Create a swap (type Linux-swap) partition twice the size of the amount of RAM you allocate to the image
5. Click Edit > Apply all operations
6. Close GParted

Back on the command prompt do (repair, check file system, journal, shutdown):

1. e2fsck -f /dev/sda1
2. fsck -n /dev/sda1
3. tune2fs -j /dev/sda1
4. shutdown -h now

Remove the CDRom device, and change the boot order back then start the Virtual machine. Issue a df -h to see if the partition has changed. It should have done!

Sometimes its better to have your virtual images running directly of LVM instead of using raw or QCow formatted files. So how do we convert? Basically you have to make sure that you have a volume group, of the right size or bigger and then dd the file into a LV on that volume group:

This should in the directory where you have the image:

Then change the configuration of your QEMU or whatever you are using on your virtualisation platform.

Sorry for the briefness of the instructions, its mainly for my own benefit and if you are doing this you should really know about LVM, dd and ls.

Here is a very simple configuration for nginx to proxy Jenkins (the new name for the un-Oracle’d Hudson)

I recently had a problem with having duplicate MAC addresses on my network for a couple of machines that I was using in a Linux KVM cluster. Flashing the firmware on the motherboards seem to have reset the MAC address to a default (thanks ASUS) that was the same on each board.

Changing the MAC address back seems like quite a hard job and looking around on the internet it seems that many people are doing this the hard way with shell scripts and so forth. Instead its easy enough to do this using the scripts that are already setting up the network for Debian (and I am sure this will work for Ubuntu just as well).

Edit /etc/network/interfaces like so:

What this is doing is manually controlling the startup and shutdown of the eth0 interface. I am using bridging on my KVM boxes, so I don’t actually have to set up the IP address (albeit DHCP or manual IP configuration), but that aside the interesting parts are what happens in pre-up. Firstly I set the hardware address to a new address (and please change it from the example above – thats not the actual one I used either), then we tell it to bring the interface up.

We also use pre-down to tell it what happens when stopping the network service.

Probably better than messing around with Shell scripts.

Really nice little round up on Quora:

http://www.quora.com/Linux/What-are-some-time-saving-tips-that-every-Linux-user-should-know

With a follow up on hacker news:

http://news.ycombinator.com/item?id=2361978

Probably going to be more of these.

As part of my on going effort for realtime web updates on one of our applications I needed to install RabbitMQ HEAD (That is the development head) with the RabbitMQ STOMP adaptor. Talking on IRC channel it was recommended to me to install from source, but unfortunately the documentation is out of date. So the following will do it cleanly:

Updated: The following will create a Debian style package and install (replace ** with the version numbering that you wish to use:

Activating the STOMP plugin:

Configuration file:

Restart to activate (the activation script for plugins is depreciated):

And you should have a working RabbitMQ on Ubuntu with a STOMP adaptor.

Wake-on-lan is incredibly useful for those scenarios where you have more than one machine on a network, but you don’t always want to have them running but they are needed sometimes.

To setup, make sure that the Motherboard and NIC support is there from your manufacturer. Sometimes it has to be enabled, such as making sure that it uses S3 for shutdown, and that PCI wake is supported.

Next you need to check support from the operating system, I am using Ubuntu 10.04, but this should work for other operating systems. Install ethtool, and then check against the ethernet adapter (eth0 in my example).

If support is enabled, but it is turned off you will see:

So we turn it on:

Now we need to make sure that its always enabled everytime we restart:

And in that file:

Now make sure that its put into the correct runlevels:

And that is it. It should be supported that you can wake the machine from another computer/server using your favourite wakeup utility ( such as wakeonlan ).

I always have this problem when moving VMWare images of Ubuntu, the most recent of a 10.04 LTS Server. Whenever you move or copy a VMWare image it assigns a new Mac address and Ubuntu starts without properly bringing up the interface.

Really annoying when you are using VMWare server without a console.

To make it grab the IP Address again, simply remove the rule:

Then restart.

Of course before you move the image you could remove the rule and not have them problem.

I am normally using Debian, Ubuntu or even Suse for deploying Django, but a recent customer needed to deploy on Red Hat Enterprise Server 5.

We decided beforehand to test deployment on RHEL5 and also on CentOS 5.4 and so these instructions should work for both environments. NginX will be used as the webserver.

The first thing I like to do is to upgrade the repository and add EPEL. This wasn’t needed I found on the RedHat box I was using, but was needed on CentOS but your mileage might vary. It should be noted that we made the system as up to date as possible with patches and yum updates.

I won’t be covering the database setup, it is assumed that this is already setup and done. I also won’t be covering the actually placing of the Django application anywhere.

Python 2.4 ships with both RHEL5 and CentOS 5 and is needed for the packaging environment YUM so I would advise not to replace it but just compile and install 2.5.5 (or 2.6) next to it.

Now we need to build and install NginX. I choose this primarily because of my experience with it, (I have used Apache2 a lot but its archaic ) and because of its speed.

There is a decent RedHat init.d script here: http://wiki.nginx.org/RedHatNginxInitScript, but remember that I have changed the installation location above so you will need to change the location in that script of nginx from /usr/sbin/nginx to /usr/local/sbin/nginx

You will also need a nginx.conf configuration script for /etc/nginx/ or you could roll your own using sites-available, sites-enabled pattern. I will attach the script soon.

Now with Python 2.5 installed we can install Django and other requirements:

I am using easy_install here as that is the most widely used tool, but pip with a requirements file is a better solution.

Now we need a database adapter. I am using PostgreSQL 8.4.2, if you are using MySQL, Oracle or some other database you will need to follow the recommended route for the Python adapter.

Change the location of pg_config:

And now install:

Then you need to install your application. This is really specific to your needs. I choose to install the files in /opt/cantemo/application-name as that is specific to our solutions, but RedHat style might mean that you wish to install somewhere else.

Lastly you will want to have your application start easily and also make sure that it starts if the machine ever reboots. To do this I am going to install the start-stop-daemon that is used on Debian based Linux distros on Redhat. I read some threads that it will but there is no ETA on that.

You should download the initd script for Django from http://code.djangoproject.com/wiki/InitdScriptForLinux. Change the RUN_AS user to the user on RedHat that you are going to use for running Nginx. By default this is apache.

Lastly make sure that your application directories have the correct user permissions but you should be able to start everything by issuing the following commands:

Eric Florenzano posted a nice tutorial on deploying django using FastCGI so also check that out, but I didn’t have much luck with daemontools on CentOS, and didn’t bother trying on RedHat. I suggest instead using start-stop-daemon. Check it out for other hints and tips though, particularly on prefork vs. threaded, pip, and more nginx configuration tips.

I have been using Hudson as a continuous integration server for a short while now and I am super impressed. I have it running on Debian and is really quite feature-full.

One thing that I did have a problem with was with the standard Debian 5 Java environment there was a problem using TLS for mail it seemed, and I didn’t just want to send stuff to gmail’s SMTP server all the time so I configured a local Postfix SMTP relay on another server.

This guide, Send Mail Postfix Through Gmail’s SMTP On A Ubuntu LTS Server helped a lot – but be sure to read the comments as there are some helpful hints.

So now I have it. Hudson running and sending email through my relay to my gmail accounts.

More information on Hudson soon.