Working with Virtual Machine images

CatN engineers spend a lot of time working with virtual machine images. We have put together this useful list of commonly used commands and procedures to help you get started on your next project.

For simplicity we assume to work with VM images created using the shell script, as explained on my previous post “Automated CentOS Virtual Machine Image Creation”.

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Add a virtual storage device to a Virtual Machine

Following our previous article about resizing virtual machine images, we now look adding an additional storage device to an existing VM. If instead you wish to extend the existing VM storage volumes, please consult the article “Resize a CentOS Virtual Machine Image“.

For simplicity we assume that the VM image you wish to extend has been created using the shell script, as explained on my previous post “Automated CentOS Virtual Machine Image Creation“.

The file-based virtual storage device acts as a virtualized hard drive for virtualized guests and its creation is quite quite straightforward.

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Resize a CentOS Virtual Machine Image

Following our series of articles about virtual machine images, we now look at a common problem faced by system engineers – what happens when you run out of disk space on your virtual machine? This guide addresses this issue and explains how to expand a CentOS Virtual Machine image, resizing any partitions contained within.

We assume that the VM image to resize has been created using the shell script, as explained on my previous post “Automated CentOS Virtual Machine Image Creation“. This is because the resizing script ( assumes details about storage volumes that rely on the having be used. In any case all the steps are illustrated here so you can adapt the commands to your needs.

The shell script is part of the CentOS-KVM-Image-Tools project that you can clone on your machine using the following command:

git clone git://

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Automated CentOS Virtual Machine Image Creation

This article shows how to create a CentOS Virtual Machine (VM) in unattended mode using a shell script and illustrates the main steps and options to reproduce the process manually.

The following script and commands will create a base image that can be used to deploy multiple nodes from a system like Ansible to define roles for each node. It is very useful for creating clustered virtual environments such as the vCluster stack.

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Building a virtual machine image for CentOS

CentOS Images Featured Header

This post describes the process of creating a CentOS virtual machine image. Creating a base or master image is incredibly useful in a cloud environment as it allows the creation of multiple nodes / VMs or guests based on the original template.

We have an existing CatN Labs project where we are hosting pre-built CentOS golden master images for use when deploying multiple nodes. You can read about the project on the CatN Labs CentOS Images page.

The base image is a static template of software including OS which is mounted when the VM runs and referenced by further clone nodes. To get started on the base template you will need to have some tools installed on your Linux node. Adapt the following commands for your distribution of choice!

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CatN goes to CentOS Dojo Antwerp

It’s no secret that we use a lot of CentOS at CatN, in fact we have deployed thousands of instances over time on both physical and virtual machines, and we have 4 Red Hat Certified Engineers (soon to be 6) on staff.

As a company with deep expertise and experience with CentOS it makes complete sense that we understand where our software comes from. You only have to look at the state of our food chain to see that interest in your upstream makes a lot of sense. At the end of the day we have to trust the food [software] that we eat [install]!

Getting to events like this is a great way to get a feel for a community, meet people and potentially find a way to contribute back into the ecosystem as well. What’s not to like about that?

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P2V migration – a live CentOS server to a KVM guest

Recently we had to migrate a live physical server into a guest running under KVM. This article describes the physical to virtual process and can be helpful if you need to clone a physical server without taking it down and run it under KVM.

Preparing virtual machine’s disk image

If you can’t take your system offline to make an image of the whole disk (because you don’t have a physical access to it or it’s an imporant live server etc.) you can still recreate the image manually with a few steps. To get a working system image you’ll have to…

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How to create TCPWebLog RPM packages for Enterprise Linux

This is a short hands-on tutorial on creating TCPWebLog RPM packages for Enterprise Linux, including, but not limited to, Red Hat Enterprise Linux (RHEL), CentOS and Scientific Linux (SL).

TCPWebLog is a Free Open Source Software system designed to collect and aggregate Web logs (i.e. Apache and Varnish) from multiple GNU/Linux computers running on a Cloud. For more information please read the blog post: TCPWebLog – Collecting and Aggregating Web Logs on the Cloud.

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Diary of a Linux n00b

If you’d asked me about Linux 3 months ago I’d have muttered about Ubuntu before quickly changing the subject to whether anyone wanted a cuppa and made a run for the nearest door; I can now proudly say I’ve configured my first LAMP stack and even edited a database with positive results!

One of the things I wanted to get my head around from week 1 was Linux, I had seen it used but that was about as far as it went. The email saying ‘why don’t you have a go at setting up a LAMP stack?’ had me quaking in my boots, but the one thing I did know about Linux was that the community support was great – so off I went to ask ‘where on earth do I begin?’
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ServerUsage – Measuring users’ activity on Linux hosts

ServerUsage is a Free Open Source Software system to collect and process usage statistic information from multiple computers running a GNU-Linux Operating System.

Since CatN is a “cluster” hosting company, one of the challenges is to track and analyse the customers’ activity spread on multiple physical hosts for both monitoring and billing purposes. From each physical host we need to collect at regular intervals the total disk I/O, the network traffic and the CPU ticks used by each system user, process and IP address. This “raw” log data must be then aggregated and processed on a central point to extract relevant information.

After spending some time searching for a ready-made solution I decided to start the ServerUsage project to best-fit our needs. This project is now available as a Free Open Source Software, so anyone can freely use and contribute to it.

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