Category Archives: Debian

Get started with InfluxDB and Python on Linux

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If you are building a script, application or anything else that collects measurements or data over time intervals, a time-series database might be a good match for you. In a TSDB you simply store the data and read it back for analysis. For these use cases, there is no need for updates or changes to the data as it’s time-based. The data can’t change back in the past. InfluxDB is the most popular of these time-series databases and this article describes how to get started with it, on Debian or Ubuntu, and how to use it from Python.

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Upgrade Debian 9 (Stretch) to Debian 10 (Buster)

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When there is a need to upgrade an existing Linux installation that has been running for some time, there is always a certain fear of breaking things. Especially if the machine has been doing it’s job fine for a long time. Unfortunately we can’t escape these kind of things and in most cases it’s better to move to a new version before it gets unsupported. Fortunately the procedure and success of this process has been greatly improved with recent versions of (Debian) Linux. This post will take you through the required steps to upgrade an existing Debian 9 to the current stable Debian 10 installation.

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Cross compiling for arm or aarch64 on Debian or Ubuntu

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ARM is gaining more and more traction and is growing a lot in popularity. It’s not always possible to build directly on these ARM-based devices, especially when they are limited in resources. The majority of build and developer machines are still on x86 and by using cross compiling, it is possible to build binaries or executables usable on another architecture. For example, to use your standard PC, most likely x86, to build something that is usable on another machine or device that’s on another architecture, like ARM. In this post, I’ll explain how to do cross compiling for 32bit ARM (arm) or 64bit ARM (aarch64) using Debian 10 or Ubuntu 20.04 LTS.

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Forward a TCP port to another IP or port using NAT with nftables

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Besides using NAT for accessing the internet with multiple machines using a single IP address, there are many other uses of NAT. One of them is to forward all traffic that is sent to a certain TCP port to another host. In practice, this technique can be used to test a service on a new host without adjusting anything on the client. The users or the clients do not need to be pointed to a new machine in order to test it. When the test would be unsuccessful, removing the NAT-rule is all it takes to switch back.

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Install a newer kernel in Debian 10 (buster) stable

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When using the latest version of Debian 10 stable, also known as buster, even with all updates installed, by default, you can’t get the most recent kernel via the standard repositories in your package manager. While the idea of using Debian stable 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 get the OS to support all your hardware. The risk and impact on stability is small and the process is rather simple.

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Build/configure a Linux-based NAS

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There are several options when you would like a NAS or Network Attached Storage. One of them is, instead of using dedicated NAS hardware, to build and configure your own (Linux-based) NAS system, using a standard distro. Getting dedicated NAS hardware has an advantage in terms of ease of use. On the other hand, building your own system and configuring the OS yourself has the advantage of flexibility, potential additional features and might even save you some money. But what about the power consumption? This post covers my journey for a self-built, Linux-based, NAS for home

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Build Docker images for deployment on non-x86 architecture

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When building a Docker container image, in most cases, the machine where you build it on runs on the same CPU architecture as where you eventually want to use it. Today, more and more, there is a need for deploying containers on a different architecture as where it was built on. The most common scenario would be to build on your regular x86 desktop and to deploy to an ARM variant.

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Install a newer kernel in Debian 9 (stretch) stable

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When using the latest version of Debian 9 stable, 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 using Debian stable 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 get the OS to support all your hardware. The risk and impact on stability is small and the process is rather simple.

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Cross compiling for ARM with Ubuntu 16.04 LTS

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The goal of cross compiling is to compile for one architecture on machine running another one. In this post, I’ll try to explain the steps required to be able to compile software that is executable on ARM-based hardware using a “normal” x64-based PC or virtual machine. ARM-based devices are usually limited in processing power and are mostly running stripped-down, embedded versions of Linux. This makes it sometimes difficult to compile on the target device directly.

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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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Create a PXE bootserver to install multiple Linux distributions

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When regularly installing Linux hosts or VM’s, it easily becomes annoying to constantly burn CD’s/DVD’s or mount ISO’s for all the Linux distributions that you want to deploy. Especially if you want to keep them current or customize them you’ll end up with a whole lot of discs. Booting your installations from the network, using a PXE boot server, makes life a lot easier and isn’t very hard to setup. In this post I’ll explain how to setup such a PXE boot server that is able to provide multiple Linux distribution installations for deployment over the network.

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Configure two network cards in a different subnet on RHEL 6, RHEL 7, CentOS 6 and CentOS 7

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When configuring a Linux host running either Red Hat Linux 6, Red Hat Linux 7, CentOS 6 or CentOS7 with two network interface cards (NIC) that each have an IP address in a different network or subnet, you could end up in a situation where one of the IP addresses isn’t reachable outside it’s own network. Both IP’s will be responding to a ping from another host in the same network as those IP addresses but only one is responding to ping from another network. On most other distributions, like Debian, this issue, which is caused by asymmetric routing, doesn’t seem to exist.

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Write to and manage syslog messages with logger and rsyslog

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Syslog is the target where you want all log message to go on all systems that you manage. Almost all Linux distributions use a syslog implementation to gather messages. Recently, rsyslog became the most used syslog-implementation for Linux. Messages can be saved locally or sent to a remote syslog server. When creating your own applications or tools or when you want to log messages coming from processes that don’t support writing to syslog directly, you can use Logger.

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Forward a TCP port to another IP or port using NAT with Iptables

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Besides using NAT for accessing the internet with multiple machines using a single IP address, there are many other uses of NAT. One of them is to forward all traffic that is sent to a certain TCP port to another host. In practice, this technique can be used to test a service on a new host without adjusting anything on the client. The users or the clients do not need to be pointed to a new machine in order to test it. When the test would be unsuccessful, removing the NAT-rule is all it takes to switch back.

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Find and recover space used by deleted files, shown by df but not by du

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When you’re running low on space on a file system, that can cause various unexpected behavior of the system, depending on which file system is filling up. For me, when that happens, I usually first issue a disk free (df) to see which is the file system that is almost full. Once I know which file system, I go and search which files take up the most space in that file system and take action. Sometimes, df show that a file system is almost full while, when summing up all the space by all files doesn’t even come near that value.

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Install and use Debian Wheezy as Xen virtualization host

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Earlier, I explained how to setup CentOS or RHEL as a KVM virtualization host. You can find that  explanation here. It also contains some basic terminology about virtualization which is also applicable for Xen. When talking about KVM, somehow, I immediately associate it with the Red Hat family just as when you talk about Xen, I associate it to Debian derivatives. So for this post, I’ll use Debian to install a host that will run Xen-VM’s by using paravirtualization.

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Mount Windows (CIFS) shares on Linux with credentials in a secure way

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In almost all cases, when mounting a CIFS-share on a Linux host, you will need to supply some credentials. Either you could enter the credentials by hand every time you need the share or add the credentials to /etc/fstab to automatically mount the share. Entering the password manually is secure but not comfortable, leaving the password in /etc/fstab is comfortable but not secure since the file /etc/fstab is world readable.

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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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