Sysadmin

Prelude This is a followup from my previous post and a sort of continuation on the series of the topic, where we are exploring ways to make our test system more “unreliable” in order to observe if our applications behave nicely under challenging and not-ideal environments. In this article we are going to explore some linux technologies: Network Namespaces (netns) Virtual Ethernet Devices (veth) Network Emulation (netem) scheduling policy The goal is to setup a virtual network link inside our system, make the two network devices talk each other and then simulate a bad/slow/glitchy/flaky communication to test how applications behave under difficult conditions. ...

“You sound like a broken record” Is something we complain when someone repeats again and again the same concepts. But even broken disks can sometime be useful DISCLAIMER: No filesystem or device were harmed in the making of this experiment 😉 Image credits: Mick Haupt In this article I would like to explore the powerful tools we have in Linux to simulate dealing with broken disks, that is, drives that more or less randomly report errors. Why is this important ? Because by simulating errors that will also happen sooner or later in the real world, we are able to create software that is more robust and can withstand any problems on the infrastructure. ...

Intro The Thinkpad P15 laptop is a nice linux machine, but there is an annoying detail, as Arch wiki writes: “The default operation of fans is noisy, as they are basically at medium power all the time. The thinkfan program can be used to create a quieter operation, while retaining reasonable temperatures.” . Let’s make it quieter. Prerequisite Install thinkfan rpm package and enable the daemon: # zypper in thinkfan && systemctl enable --now thinkfan Make sure modules are loaded at startup with the options to override fan control and enable experimental features: ...

As you may know, you can configure any DHCP server to send many options to the clients; for example to setup dns domains, http proxy (WPAD) and so on. If you need to access these options from a linux client, you must configure the client to ASK the server for the new options, by editing /etc/dhcp/dhclient.conf, and add an entry like: option WPAD code 252 = string; also request WPAD; done that, when you’ll ask for a dhcp, the dhclient process will invoke your hook scripts with two new environment variables, old_WPAD and new_WPAD, with the values before and after the renewal. ...