Skip to content

Notes from The Linux Foundation Courses

Introduction to Linux - LFS101

The Three "Main" Families of Linux

There are three major families of Linux distributions:

  • Red Hat
  • SUSE
  • Debian

Red Hat Family Systems (incl CentOS, Fedora, Rocky Linux)

Red Hat Enterprise Linux (RHEL) heads up the Red Hat family.

  • The basic version of CentOS is virutally identical to RHEL.
    • CentOS is a close clone of RHEL, and has been a part of Red Hat since 2014.
  • Fedora is an upstream testing platform for RHEL.
  • Supports multiple hardware platforms.
  • Uses dnf, an RPM-based package manager to manage packages.
  • RHEL is a popular distro for enterprises that host their own systems.

SUSE Family Systems (incl openSUSE)

SUSE (SUSE Linux Enterprise Server, or SLES) and openSUSE are very close to each other, just like RHEL/CentOS/Fedora.

  • SLES (SUSE Linux Enterprise Server) is upstream for openSUSE.
  • Uses zypper, an RPM-based package manager to manage packages.
  • Includes YaST (Yet Another Setup Tool) for system administration.
  • SLES is widely used in retail and other sectors.

Debian Family Systems (incl Ubuntu and Linux Mint)

Debian provides the largest and most complete software repo to its users of any other Linux distribution.

  • Ubuntu tries to provide a compromise of long term stability and ease of use.
  • The Debian family is upstream for several other distros (including Ubuntu).
    • Ubuntu is upstream for Linux Mint and other distros.
  • Uses apt, a DPKG-based package manager to manage packages.
  • Ubuntu is widely used for cloud deployments.

Linux History Overview

Linux is an open-source OS. Initially developed on and for intel x86-based PCs. Since then, it's been ported to many other hardware platforms, from embedded appliances to the world's biggest supercomputers.

Linux, the kernel, was started in 1991 by Linus Torvalds.
In 1992, Linux was re-licenced with the GPL by GNU, the operating system, which is from the Free Software Foundation (FSF), which promotes freely available software.

Combining the kernel with other systems from the GNU project, other developers create complete operating systems - Linux distributions - which first appeared in the mid 90s.

In 1998, major companies (IBM and Oracle) announced their support for the Linux platform. These companies then began major development efforts too.

Today, Linux is used by more than half of the servers on the internet, the majority of smartphones (via Android, which is built on top of Linux), more than 90% of the public cloud workload, and all of the world's most powerful supercomputers.

The Linux Philosophy

Linux borrows a lot from UNIX operating systems. It was written to be a free and opern source alternative.

Files are stored in a hierarchial filesystem. The top node of the system is root (or just /).
Whenever possible, Linux makes everything available as files or objects that look like files.
Processes, devices, and network sockets are all represented by file-like objects.
These can often be worked with using the same tools used for regular files.

Linux is a fully multitasking OS, meaning multiple threads of execution are executed simultaneously. Linux is also a multiuser operating system with builtin networking an service processes known as "daemons".

The Linux Community

The Linux community is made up of people across the world in many different roles.
Developers, system administrators, users, and vendors, all connect with each other in many ways.

  • IRC (Internet Relay Chat), like with WeeChat, HexChat, Pidgin, XChat, etc.
  • Linux User Groups, both local and online.
  • Newsgroups and mailing lists (incl the Linux Kernel Mailing List)
  • Online communities and discussion boards
  • Collaborite projects hosted on Github/Gitlab
  • Community events (hackathons, install fests, open source summits, embedded linux conferences, etc.)

The site linux.com is hosted by the Linux Foundation. It has news, discussion threads, and free tutorials and tips.

Linux Terminology Overview

Some common terminology you'll see in Linux:

  • Kernel: The glue between the hardware and applications.
  • Distributon: Collection of software, combined with the Linux kernel, making up a Linux-based OS
  • Boot Loader: Program that boots the operating system (GRUB/ISOLINUX)
  • Service: Program that runs as a background process
    • E.g.: httpd, nfsd, ntpd, ftpd, sshd, named, etc.
  • Filesystem: Methods for storing and organizing files.
    • E.g., ext3, ext4, FAT, XFS, NTFS, Btrfs (butterFS), ZFS, etc.
  • X Window System: Graphical subsystem on nearly all Linux systems.
  • Desktop Environment: The GUI on top of the operating system, using the X Window system.
    • E.g., GNOME, KDE, Xfce, Cinnamon, MATE, Fluxbox, etc.
  • Command Line: Interface for typing commands on top of the operating system
  • Shell: The command line interpreter. Interprets the command line input and instructs the OS to perform any necessary tasks and commands.
    • bash, sh, tcsh, zsh, fish, ksh

Definition of Linux Distributions

A Linux distribution consists of the Linux kernel, plus a number of other software tools for file-related operation, user management, and software package management.

Each of those tools provides a part of the complete system. Each tool is usually its own separate project.

The most recent Linux kernel, and earlier versions, can be found in the Linux Kernel Archives.

Linux distributions may be based on different kernel versions. The RHEL 8 Linux distribution is based on the 4.18 kernel, which isn't new but is very stable. RHEL 9 is based on the much newer 5.14 kernel.

The kernel is not an all-or-nothing proposition; many distributions include customized versions of older versions of the kernel.
RHEL/CentOS has incorporated many of the more recent kernel improvements by using a CUSTOMIZED older version of the Linux kernel, as have Ubuntu, openSUSE, Fedora, etc..

Other essential tools that make up distributions: C/C++ and Clang compilers gdb debugger core system libraries, which applications need to link with in order to run Low-level interface for rendering graphics on the screen Higher-level desktop environment Package managers. Systems for installing and updating various components (including the kernel itself).

Who Uses What Distros?

CentOS and CentOS Stream are popular free alternatives to RHEL.
Large organizations (enterprise/gov't) tend to choose the major commercially-supported distros from Red Hat, SUSE, and Canonical (Ubuntu).

The RHEL variants (CentOS, AlmaLinux) are designed to be binary-compatible with RHEL... In most cases, binary software packages will install properly across all these distributions.

Ubuntu and Fedora are widely used by developers, and are popular in the educational realm.

Commercial distributors (Red Hat, Ubuntu, SUSE, and Oracle) provide long term fee-based support for their distros, as well as hardware and software certification.

All major distributors provide update services to keep the system updated with security patches, bug fixes, and performance improvements.