Professionally administering Linux is a very complex matter: it requires advanced skills on the kernel and on a lot of tools and utilities that are often combined in pipelines and scripts.

Professionals having a thorough understanding of the kernel know how to get optimal performance for specific workloads by tuning the right “knobs” and to what degree to do it. In addition to that they know what commands and tools should be used to gather all the information necessary to fix performance issues. This of course requires having a thorough understanding of the kernel scheduler, of memory allocators, of the virtual memory, the Virtual File System and so.

As anybody would expect, skilled professionals thoroughly know the Linux distribution they use – being able to install and remove software packages is absolutely not enough. They should know:

the file system standard layout used by the distro – so to honour it when installing custom software
how to create custom packages (such as RPM) to ease the installation of custom application and scripts
the peculiarities of the initialization process specific of the distribution, in order to sort out boot issues that may arise sooner or later
how to perform automated installations
how to use filesystems, partitioning and Logical Volume Management utilities to apply changes while keeping online the system

And of course a lot of other stuff.

Puppet agent on Red Hat Network Satellite Clients

Posted on February 26, 2022March 9, 2022 by Marco Antonio Carcano

Red Hat Network Satellite Server, as well as its upstream project Katello, enables you to easily manage the registered client hosts using Puppet: for this to work, you must first install the Puppet agent on the client host and register it to the Puppet master instance that is running on the Satellite (or on the Capsule).

This post is a step by step guide that does not only show you how to install and configure the Puppet agent on the client host: it also thoroughly describe how to create the Puppet product on the Red Hat Network Satellite Server 6 (or Katello), add repositories for the relevant architecture families, assign them to the right Content View and publish them into the right Lifecycle Environment.

The Linux distribution used in the examples is CentOS 7, but you can of course easily adapt it to any other Red Hat and derived Linux distribution.

Mind that configuration management using Puppet is the oldest way of managing registered hosts on Satellite: the current way is using Ansible. Red Hat announced Puppet deprecation by Red Hat Network Satellite Server 7.0 in 2020. For this reason my suggestion is to quickly migrate from Puppet to Ansible. If you want to learn more on using Ansible with Satellite, please read Enable And Configure Ansible On Red Hat Network Satellite.

Register Clients To Satellite Server 6 Or Katello

Posted on February 12, 2022March 10, 2022 by Marco Antonio Carcano

Red Hat Network Satellite Server 6, as well as its upstream project Katello, has been developed to provide software to client hosts, as well as manage their configuration sending SSH remote commands or leveraging on Puppet or Ansible.

The published packages are provided by the means of content views with frozen packages versions.

The obvious requirement to benefit from the provided services is registering client hosts. This post shows how to register clients on Red Hat Network Satellite Server 6 or Katello, providing all the necessary information to be skilled enough on subscription-manager to be able not only to operate it, but to successfully troubleshoot when it is not working as expected.

In addition to that, we also see how to enable and configure SSH based remote actions and how to run an existing Job Template..

Sed – the Stream EDitor

Posted on December 30, 2021January 2, 2022 by Marco Antonio Carcano

Sed is a command line tool that can really do amazing stream manipulations: despite it certainly being a "seasoned" tool, it is very likely that there are a lot of sed one-liners inside your Company's scripts.

Having at least an understanding of it is a must if you want to be able to maintain this legacy stuff that very often is not worth the effort to rework.

And anyway, when having to deal with quick and dirty solutions that rely on shell scripts, or when writing documentation with shell commands that can be easily replaced by a copy and paste by the reader... it's still an excellent tool honestly I cannot work without.

The aim of this post is to provide an easy tutorial to quickly learn how to use sed in every situation that can be easily sorted out with a sed one-liner.

In memory of Lee E. McMahon, contributor to early versions of the Unix operating system, ... and of course in particular of the sed stream editor.

POSIX compliant filesystems

Posted on May 3, 2021June 28, 2021 by Marco Antonio Carcano

Don’t be tempted to skip this post: you would miss something valuable. Of course most of us know how to operate a filesystem, but the underlying details of POSIX filesystems are not broadly known by most of the people. In this post I describe them quite accurately, trying to keep at a level that may intrigue, but avoiding to be too theoretical. Having such an expertise is certainly one of the things that make the difference from a technician and a skilled professional. In addition to that, this skill may really save your life when facing weird things that sometimes may arise.

Memory Management – The Buddy Allocator

Posted on April 9, 2021October 6, 2022 by Marco Antonio Carcano

Every skilled professional should have an understanding of how the kernel does allocate memory: sooner or later it happens to get a system stuck complaining that it cannot allocate memory, despite the output of the "free" command showing that there's plenty of memory. This can get people confused, however this only means that the system cannot allocate kernel memory, despite it can still allocate system memory. The aim of this post is to clarify how the kernel allocates physical memory using the buddy algorithm, along with the available tools to check the state of physical memory.