Category Archives: Linux

Split horizon DNS master/slave with Bind

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Split horizon is the ability for a DNS-server to give a different answer to a query based on the source of the query. A common use-case is when using the same DNS-server for internal and external queries. When your DNS is publicly available, you really don’t want to enable recursion to the outside world but internally it could be handy. Besides security there are also examples where resolving a certain name needs to return an internal IP while externally that IP is useless and it’s better to return something else.

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Basic master and slave DNS setup with Bind

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DNS or Domain Name System is one of the most important building blocks of the modern IT and internet. DNS allows you to use meaningful names instead of IP addresses. Especially since IPv6 is getting more popular, DNS remains a very important part of your network. This article will describe how to set up a basic master DNS-server and a slave which will replicate the data from the master.

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Building a high-available failover cluster with Pacemaker, Corosync & PCS

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When running mission-critical services, you don’t want to depend on a single (virtual) machine to provide those services. Even when your systems would never crash or hang, from time to time you will need to do some maintenance and restart some services or even the whole machine. Fortunately, clusters were designed to overcome these problems and give the ability to reach a near 100% uptime for your services.

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Install MATE or XFCE on CentOS 7

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Which desktop environment you prefer is very personal. Each of them has its advantages and, unfortunately, also its disadvantages.

Recently, I started to like MATE since it’s lightweight and customizable in a way I personally like. Before, I was a fan of XFCE for similar reasons but somehow I got a little tired and irritated of it’s shortcomings.

This post covers how to install any of those on top of a minimal install since this means it can be installed on top of almost every type of installation in regards to package selection and dependencies.

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Use iptables instead of firewalld in RHEL 7 or CentOS 7

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If you, like me, can’t get used to the “new” firewalld in RHEL/CentOS 7 or you have some automation scripts that expect iptables, then I’ve got good news for you :) It’s rather easy to disable firewalld and go back to a “normal” iptables configuration as it used to be.

There are no special tricks involved and/or custom actions that would break your system or put it in a way that you have to be affraid of updating.

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Migrate RHEL7 to CentOS7

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A migration from RHEL7 to CentOS7 could be something that is needed in certain cases. While re-installing the OS and tranferring your files and settings is not undoable, it creates a lot of effort and possible chance for downtime. Therefor it’s much more handy when an in-place migration between the two can be done. CentOS uses the same package-source as RHEL and tries to be as close as it can be to Red Hat with their distribution. It’s basically RHEL without logo’s, support and licensing.

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Install a newer kernel in Debian 7.5 (Wheezy) or CentOS 6.5

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When using the latest version of Debian Wheezy or CentOS 6.5, even with all updates installed, by default, you can’t get a very recent kernel via the standard repositories in your package manager. While the idea of both distributions is to remain stable and rather conservative, there are several benefits with installing a newer kernel and in some cases it’s the only option to run one of these distributions. The risk and impact on stability is small and the process is rather simple.

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SSD optimize your Linux

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SSD drives became a common storage-device for most computer enthusiasts and while they have a lot of advantages in comparison with the “traditional” hard disk, it’s main disadvantage is that the write-operations are theoretically limited. This process is called wearing. In order to prevent your SSD from wearing out, to maximize it’s lifespan and to  improve it’s performance, you can performthe following steps:

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