Monthly Archives: June 2015

SELinux in a practical way

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SELinux is often seen as an evil, complex, unnecessary and especially annoying security component which exists in a lot of Linux distributions. Often you can hear something like: “Disable SELinux and try again” or , “The first thing I do on a new server is to disable SELinux”. The problem with SELinux is that it looks very complex and that it looks like you need to spend ages to understand it. In this post, I’ll try to explain a few basic SELinux principles and especially focus on daily, practical problems related to SELinux and their solutions. Don’t forget that there’s a very good reason for SELinux and it would be a shame to not use it.

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Setup roundcube webmail as a proxy for Gmail

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Recently, I was asked to find a solution or workaround for people using Gmail and are visiting countries where there’s limited or no access to Gmail. I’m not talking about bad internet connection quality but about an explicit (government) block on Gmail or related websites. An example is the block on Gmail by the Chinese Great Firewall. While there is a possibility to avoid the limitation by using a normal proxy or VPN connection, those methods are also actively blocked and monitored. A workaround is to setup your own webmail, as a proxy for Gmail.

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Setup a redundant PostgreSQL database with repmgr and pgpool

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Using a database to store information is very common. The more information gets stored in a database, the more critical it becomes. At a certain point, the need for a redundant, high(er) available database-setup raises. When you’re using PostgreSQL, you can setup streaming replication quite easily in order to have your data redundant on two or more nodes. But wouldn’t it be a shame if you wouldn’t use the copies of your data to balance the load of your primary database-server? In this post, I’ll try to explain how to setup a redundant PostgreSQL database with load balancing.

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Tips & tricks for Ansible

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Ansible is a very powerful configuration management tool. It can be used to deploy settings and software to one or more (virtual) machines. Using a CM-tool ensures that every deployment is done in exactly the same way. This doesn’t only make your job as a system engineer a whole lot easier, it also results in a more stable environment since every machine is consistent and more predictable. I’m using Ansible intensively for quite some time now and found that it was time to write a post about some small, but usually hard to find or annoying to solve, problems or challenges.

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Complile and use a realtime kernel on CentOS 7 or RHEL 7

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While the need for a realtime kernel or kernel-rt hasn’t been very high recently, there are these special cases where you really need one. A “standard” linux kernel is fast but also balanced in order to treat all workload fair and give each kind of task an equal share of the system resources. A realtime kernel allows you to squeeze that extra bit of performance out of the kernel. It basically allows you to tune it in a more aggressive way in regards to timing and priorities. Since I couldn’t find any clear instructions on how to get a realtime kernel for CentOS 7 and RHEL 7, I decided to write them myself.

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