EITC/IS/LSA Linux System Administration

Debian, Fedora, and Ubuntu are all popular Linux distributions. Red Hat Enterprise Linux and SUSE Linux Enterprise Server are two commercial distributions. A windowing system like X11 or Wayland, as well as a desktop environment like GNOME or KDE Plasma, are included in desktop Linux distributions. Server distributions may or may not include graphics, or may include a solution stack such as LAMP. Anyone can produce a distribution for any purpose because Linux is a freely redistributable open-source software.

Linux was created for Intel’s x86 architecture-based personal computers, but it has subsequently been ported to more platforms than any other operating system. Linux has the greatest installed base of all general-purpose operating systems due to the dominance of the Linux-based Android on smartphones. Despite the fact that Linux is only used by only 2.3 percent of desktop computers, the Chromebook, which runs the Linux kernel-based Chrome OS, dominates the US K–12 education market and accounts for about 20% of all sub-$300 laptop sales. Linux is the most popular operating system for servers (about 96.4 percent of the top 1 million web servers run Linux), as well as other big iron systems like mainframe computers and TOP500 supercomputers (since November 2017, having gradually eliminated all competitors).

Linux is also available for embedded systems, which are devices whose operating system is often incorporated in the firmware and is highly customized to the system. Routers, automation controls, smart home technology, televisions (Samsung and LG Smart TVs use Tizen and WebOS, respectively), automobiles (Tesla, Audi, Mercedes-Benz, Hyundai, and Toyota all use Linux), digital video recorders, video game consoles, and smartwatches are all examples of Linux-based devices. The avionics of the Falcon 9 and Dragon 2 are based on a customized version of Linux.

Linux is one of the most renowned examples of free and open-source software collaboration. Under the rules of its individual licenses, such as the GNU General Public License, the source code may be used, updated, and distributed commercially or non-commercially by anybody.

The Linux kernel was not designed, but rather evolved through natural selection, according to several open source developers. Although the Unix architecture acted as a scaffolding, Torvalds believes that “Linux evolved with a lot of mutations – and because the mutations were less than random, they were faster and more directed than alpha-particles in DNA.” The revolutionary characteristics of Linux, according to Eric S. Raymond, are social rather than technical: before Linux, sophisticated software was painstakingly built by small groups, but “Linux grew up in a very different way. It was hacked on almost inadvertently from the start by large groups of volunteers who communicated solely through the Internet. The stupidly simple technique of publishing every week and receiving input from hundreds of users within days, generating a form of quick Darwinian selection on the mutations brought by developers, rather than rigorous standards or dictatorship, was used to preserve quality.” “Linux wasn’t designed, it evolved,” says Bryan Cantrill, an engineer for a competing OS, but he sees this as a limitation, claiming that some features, particularly those related to security, cannot be evolved into, because “this isn’t a biological system at the end of the day, it’s a software system.” A Linux-based system is a modular Unix-like operating system that draws much of its architectural inspiration from Unix principles developed in the 1970s and 1980s. A monolithic kernel, the Linux kernel, is used in such a system to handle process control, networking, peripheral access, and file systems. Device drivers are either built into the kernel directly or added as modules that are loaded while the system runs.

The GNU userland is an important feature of most Linux-based systems, with Android being an exception. The toolchain is a broad collection of programming tools vital to Linux development (including the compilers used to build the Linux kernel itself), and the coreutils implement many basic Unix tools. The Project’s implementation of the C library works as a wrapper for the Linux kernel’s system calls necessary to the kernel-userspace interface, the toolchain is a broad collection of programming tools vital to Linux development (including the compilers used to build the Linux kernel itself), and the coreutils implement many basic Unix tools. Bash, a popular CLI shell, is also developed as part of the project. Most Linux systems’ graphical user interface (or GUI) is based on an implementation of the X Window System. More recently, the Linux community has been working to replace X11 with Wayland as the replacement display server protocol. Linux systems benefit from several other open-source software initiatives.

A Linux system’s installed components include the following:

• GNU GRUB, LILO, SYSLINUX, or Gummiboot are examples of bootloaders. This is a software that executes when the computer is powered on and after the firmware initialization to load the Linux kernel into the computer’s main memory.
• An init program, such as sysvinit or the more recent systemd, OpenRC, or Upstart. This is the initial process started by the Linux kernel, and it sits at the top of the process tree; in other words, init is where all other processes start. It initiates tasks like system services and login prompts (whether graphical or in terminal mode).
• Software libraries are collections of code that can be utilized by other programs. The dynamic linker that handles the use of dynamic libraries on Linux systems employing ELF-format executable files is known as ld-linux.so. If the system is set up so that the user can generate applications themselves, header files will be included to describe the installed libraries’ interface. Aside from the GNU C Library (glibc), which is the most widely used software library on Linux systems, there are other more libraries, such as SDL and Mesa.
• The GNU C Library is the standard C standard library, which is required to run C programs on a computer system. Alternatives for embedded systems have been developed, including musl, EGLIBC (a glibc clone originally used by Debian), and uClibc (built for uClinux), however the last two are no longer maintained. Bionic, Android’s own C library, is used.
• GNU coreutils is the standard implementation of basic Unix commands. For embedded devices, there are alternatives such as the copyleft BusyBox and the BSD-licensed Toybox.
• Widget toolkits are libraries for creating software applications’ graphical user interfaces (GUIs). GTK and Clutter, created by the GNOME project, Qt, developed by the Qt Project and led by The Qt Company, and Enlightenment Foundation Libraries (EFL), maintained mostly by the Enlightenment team, are among the widget toolkits available.
• A package management system, such as dpkg or RPM, is used to manage packages. Packages can also be built from source tarballs or binary tarballs.
• Command shells and windowing environments are examples of user interface programs.

The user interface, often known as the shell, is typically a command-line interface (CLI), a graphical user interface (GUI), or controls coupled to the accompanying hardware. The typical user interface on desktop PCs is usually graphical, while the CLI is frequently accessible via terminal emulator windows or a separate virtual console.

Text-based user interfaces, or CLI shells, employ text for both input and output. The Bourne-Again Shell (bash), which was created for the GNU project, is the most widely used shell under Linux. The CLI is used entirely by most low-level Linux components, including various sections of the userland. The CLI is especially well-suited to automating repeated or delayed operations, and it allows for relatively easy inter-process communication.

The GUI shells, packed with full desktop environments such as KDE Plasma, GNOME, MATE, Cinnamon, LXDE, Pantheon, and Xfce, are the most popular user interfaces on desktop systems, while a number of other user interfaces exist. The X Window System, also known as “X,” underpins the majority of popular user interfaces. It enables network transparency by allowing a graphical application operating on one machine to be displayed on another, where a user can interact with it; however, some X Window System extensions are not capable of working over the network. There are several X display servers, the most popular of which is X.Org Server, which is the reference implementation.

Server distributions may provide a command-line interface for developers and administrators, but may also include a bespoke interface for end-users that is tailored to the system’s use-case. This custom interface is accessed via a client running on a different system that isn’t necessarily Linux-based.

For X11, there are several types of window managers, including tiling, dynamic, stacking, and compositing. Window managers interact with the X Window System and allow you to control the location and appearance of individual application windows. Simpler X window managers like dwm, ratpoison, i3wm, or herbstluftwm have a minimalist interface, whereas more complex window managers like FVWM, Enlightenment, or Window Maker include additional features like a built-in taskbar and themes, but are still lightweight when compared to desktop environments. Window managers such as Mutter (GNOME), KWin (KDE), and Xfwm (xfce) are included in most desktop environments’ basic installations, but users can choose to use a different window manager if they prefer.

Wayland is a display server protocol that was designed to replace the X11 protocol, however it has yet to gain widespread use as of 2014. Wayland, unlike X11, doesn’t require an external window manager or compositing manager. As a result, a Wayland compositor serves as a display server, window manager, and compositing manager all in one. Wayland’s reference implementation is Weston, although Mutter and KWin from GNOME and KDE are being converted to Wayland as standalone display servers. Since version 19, Enlightenment has been successfully ported.