Linux Tech Tips

Migrating to another virtual machine program can be intimidating. if you already have your virtual machines set up they way you like them, you don’t necessarily have to install them from scratch – you can migrate your existing virtual machines. VirtualBox and VMware use different virtual machine formats, but each supports the standard Open Virtualization Format. Convert your existing virtual machine to OVF or OVA and you’ll be able to import it into another virtual machine program. Unfortunately, this may not always work perfectly, as VirtualBox and VMware both seem to use slightly different OVA/OVF implementations that aren’t entirely compatible. If this doesn’t work, you may want to reinstall your virtual machine’s guest operating system from scratch. VirtualBox to VMware Before migrating a virtual machine from VirtualBox to VMware, ensure it’s “powered off” in VirtualBox – not suspended. If it’s suspended, launch the virtual machine and shut it down. ...

Just because Tomcat is a lightweight container with a small footprint doesn't mean it isn't ready to deliver big performance under real-world loads. Tomcat's built-in support for clustering, load balancing, and session persistence means that you can add more power to your network as you need it, allowing your site to scale with your user base. In this article, we'll go over the basic concepts behind clustered architecture, such as load balancing and session persistance, look at some different ways to approach these problems, and then show you how easy it is to set up your own Apache Tomcat clusters. How Clustering Works Although clustering is most frequently talked about in relation to scalability, most modern clustering solutions actually attack a number of related issues in addition to simply providing more CPUs to serve requests. A typical clustering solution aims to provide not only scalability, but also high availability and load balancing. Be...

Guide to Tomcat Clustering Apache Tomcat is a great performer on its own, but if you're expecting more traffic as your site expands, or are thinking about the best way to provide high availability, you'll be happy to know that Tomcat also shines in a clustered environment. With built-in support for both synchronous and asynchronous in-memory and external session replication, cluster segmentation, and compatibility with all common load balancing solutions, your Tomcat servers are ready for the cluster right out of the box. In this article, we'll show you how easy it is to set up a simple Tomcat cluster with load balancing and session replication. This simple step-by-step guide will walk you through every step of the process in plain English, from installing the load balancer, to configuring mod_jk, to enabling Tomcat's built-in session replication capabilities. Along the way, we'll point out common problem areas, to help you avoid configuration mistake...

Why Bother? Why do you need to learn the command line anyway? Well, let me tell you a story. A few years ago we had a problem where I used to work. There was a shared drive on one of our file servers that kept getting full. I won't mention that this legacy operating system did not support user quotas; that's another story. But the server kept getting full and it stopped people from working. One of our software engineers spent the better part of a day writing a C++ program that would look through all the user's directories and add up the space they were using and make a listing of the results. Since I was forced to use the legacy OS while I was on the job, I installed a Linux-like command line environment for it. When I heard about the problem, I realized I could do all the work this engineer had done with this single line: du -s * | sort -nr > $HOME/user_space_report.txt   Graphical user interfaces (GUIs) are helpful for many tasks, but they are not good f...

Many of us who love to work on Linux enjoy the privilege of using a plethora of commands and tools. Here is our effort to introduce you to a few very simple- to-use, yet enormously effective commands. The intended audience may belong to all classes of Linux users and the only requirement is to have a basic acquaintance with Linux. Our article deals with bash shell and Linux version Fedora 9, kernel 2.6.25. Often, commands on the console may span many lines, and encountering a type mistake at the beginning of the command would require you to use the slow way of punching the right/left arrow keys to traverse in the command string. Remedy: Try Ctrl+e to move to the end of the command string and Ctrl+a to reach start. It’s the fastest way to edit a Linux command line. To delete a word in the command string, use Ctrl+w. Another wonder of a simple shell variable is !$ . Let’s say you have to create a directory, go into it and then rename it. So the flow of commands would ...

Last July, Microsoft announced the drivers for Linux source code is available in the Hyper-V virtualization environment. In practice, the 2.6.32 of the Linux kernel version now contains drivers for synthetic Hyper-V, virtual machine including the VMBus, storage, and network components. In detail, it's hv_vmbus, hv_storvsc, hv_blkvsc and hv_netvsc modules. These modules are described in t his article . Out configurations "officially supported", I tested the activation of these modules in new Ubuntu Server 10.04, provided recently with the 2.6.32 kernel. To do this I found this article which explains how to enable these modules, and which I inspire me thus far. Enabling modules Firstly it must ensure that the Hyper-V modules are loaded at startup. To do this, edit the file /etc/initramfs-tools/modules and add the following four lines: hv_vmbus hv_storvsc hv_blkvsc hv_netvsc Then, update the initramfs image: $ sudo update-initramfs...