Miscellaneous Articles

Although the ISPmail guide is the key part of this web site, there are further articles on various topics. Those have been gathered here.

Zabbix

Tips and tricks for the Zabbix monitoring software

  • Making the best of Zabbix maps

    There are different ways to access the data that Zabbix has gathered for you. If you are looking for a graphical way then you will want to try out maps. In this article I will give you an example on how to create useful maps and add live data to labels. Read More

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  • Zabbix: How escalations work

    Zabbix is a very complex software that takes weeks to fully understand. One interesting,complex and badly documented feature is escalations. They define what should happen when a certain event occurs. Like waking up the system administrator or doing some automatic emergency cleanup tasks. Read More

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Padrino

Padrino is a nice lightweight web framework in Ruby for developers who don’t like the monolithic approach of Ruby on Rails.

Squid

Snippets and explanations for the Squid caching proxy.

  • Writing Squid authenticators

    An authenticator that you can use in Squid is pretty simple. So if you find you need to use an authentication scheme that is not yet supported you can pretty easily write one yourself. All you need is some basic knowledge of scripting languages (bash, Perl, Python, whatever). The authentication requests are passed to the… Read More

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  • Nagios plugin for checking Squid

    I once needed a way to make sure our Squid proxy cluster operates correctly. So I wrote a rather simple Squid check plugin for the Nagios monitoring software. André Moura has pimped it further. Feel free to use it. It’s also available from monitoringexchange.org. Read More

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  • Squid log reader

    Reading Squid’s log files can be hard for us humans. This Perl script will help you decipher them. Note that since Squid version 2.6 you can customize the log format. See http://www.squid-cache.org/Doc/config/logformat/ for details. I personally prefer this log format: logformat squid %{%d.%m.%Y-%H:%M:%S}tl.%tu %6tr %>a %Ss/%03Hs %<st %rm %ru %un %Sh/%<A %mt #!/usr/bin/perl -w #… Read More

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  • Using LDAP to authenticate Squid proxy users

    This article is meant to help set up LDAP authentication with a Squid proxy. Often administrators are using Squid as the central proxy for a company. For security reasons users need to enter their username and password before they are allowed to surf the internet. Firewalls usually deny accesses to the internet that would bypass… Read More

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  • How to keep your users from bypassing your proxy

    Many administrators do not seem to recognize the true purpose of a proxy. That is to make sure nothing but a certain protocol is used through the proxy. Squid is a HTTP proxy. It makes sure that people use nothing but HTTP through it. I apologize if I sound rude but from listening to other… Read More

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  • Controlling how your users surf the internet with Squid

    How to keep your users from bypassing your proxy Many administrators do not seem to recognize the true purpose of a proxy. That is to make sure nothing but a certain protocol is used through the proxy. Squid is a HTTP proxy. It makes sure that people use nothing but HTTP1 through it. I apologize… Read More

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  • How Squid ACLs work

    For less experienced Squid administrators the concept of ACLs can be confusing at first. But they offer a great way of controlling who is allowed to access which web pages when. ACLs First you need to define certain criteria like accesses from the marketing department or accesses to google.com or need to authenticate. There are… Read More

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Linux tips

Findings and guides that help you understand and work with your favorite Linux distribution.

  • Understanding the Logical Volume Manager (LVM)

    What is LVM and what does it offer? LVM is a neat feature that some system administrators still shy away from. But it’s really not that hard to learn. And these are some awesome features you get: LVM is just a thin layer of software between the disks on your system and the partitions. On… Read More

  • Debian packages are so old

    Debian comes with tens of thousands of software packages that you can easily install on your system. But Debian only publishes a new “stable” release every 2-3 years. That creates the impression that Debian packages must always be up to 3 years old. And who wants to work with a three year old piece of… Read More

  • Updating the BIOS on Lenovo laptops from Linux using a USB flash stick

    Aren’t hardware manufacturers funny? They either require an old-fashioned operating system (Windows) or museum hardware (floppy drives) to update a BIOS. Apparently they never learn and are instead busy adding features like DRM and UEFI to make our lives even more miserable. However updating the BIOS on my Lenovo X230 laptop was surprisingly easy once… Read More

  • Docking and undocking Linux laptops with nVidia GPUs using disper

    Do you have trouble switching the display when docking and undocking your Linux laptop? In this article I will show you how to use disper and keyboard shortcuts to do that reliably if you are using nVidia’s annoyingly broken RandR-incompatible graphics driver. Many companies nowadays give their employees laptops instead of classical PCs under their desks. And… Read More

  • Backups with rsnaphot to external USB drives

    How long has it been since you last backed up your Linux system? Let me guess – you tried various backup systems and hate all of them? Let me show you how to use rsnapshot and an external inexpensive USB drive to back up precious data easily. Read More

  • Renaming multiple files

    If you need to rename a larger number of files following a certain pattern then you will long for an automated solution. The ‘rename’ command helps you here that is (at least on my Debian installation) part of the Perl installation. All you need to know is the basics of regular expressions to define how the… Read More

  • Pipes and redirection

    Many system administrators seem to have problems with the concepts of pipes and redirection in a shell. A coworker recently asked me how to deal with log files. How to find the information he was looking for. This article tries to shed some light on it. Input / Output of shell commands Many of the… Read More

  • Using tcpdump and Wireshark to sniff and analyse your network traffic

    Sometimes a network service is just not behaving the way it should. And the log files do not help you either. Then it is time to use the power of tcpdump and Wireshark to get a deeper look on what is actually happening on the wire. If you have an X11 running on the host… Read More

  • Mounting flash sticks or memory cards on Debian

    Usually modern desktop Linux distributions make it easy to automatically mount external storage media like USB flash sticks. But if all else fails this article may help you. Kernel Compile a kernel with SCSI disk support (CONFIG_BLK_DEV_SD), multiple LUN support (CONFIG_SCSI_MULTI_LUN – otherwise the x-in-1 card reader will not work) and USB storage support (CONFIG_USB_STORAGE). Plug… Read More

  • Bareos/Bacula Cheat Sheet

    Bacula is a nifty backup software that is network-capable and stores data in the database for faster retrieval in case you need a certain file back. As a big fan of cheat sheets I created this cheat sheet. What’s up? Which files shall be backed up? show filesets I=Included, E=Excluded What’s the server doing? status… Read More

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