Linux Distributions: Red Hat & SUSE Families

Linux Foundation

• The Linux kernel is at the core, and distros are built around it.
• Key Distro Families: Debian, RHEL, SUSE
• Key Individual Distros: Ubuntu, Linux Mint, CentOS, Fedora, openSUSE, SLES

Red Hat Family

• Consists of RHEL, CentOS, CentOS Stream, Fedora, Oracle Linux.
• Supports multiple hardware systems, used by enterprises hosting their own systems.
• Fedora contains more software than RHEL and uses a more diverse community in building it.
• Fedora serves as an upstream testing platform for future RHEL releases.
• CentOS and CentOS Stream are no cost to end users with a longer release cycle than Fedora.
• CentOS is virtually identical to RHEL.
• CentOS Stream receives updates prior to RHEL, while CentOS is updated post RHEL.

SUSE Family

• Consists of openSUSE and SLES.
• openSUSE is a reference distribution available at no cost for end users.
• SLES (SUSE Linux Enterprise Server) is upstream for the SUSE family, used in the retail sector.
• RPM-based zypper package manager is used for installing, removing, as well as updating packages.
• YaST (Yet Another Setup Tool) is used for administration.

Debian Family

• Debian is upstream for distros like Ubuntu, which in turn is upstream for Linux Mint.
• It is used in both server and desktop computers, with a focus on stability and open source.
• It is also used for cloud deployments.
• Debian has the largest and most complete software repository for its users.
• Ubuntu balances stability and ease of use, drawing packages from the stable Debian branch.
• It is built on Debian, uses GNOME under the hood, and differs visually from standard Debian.
• Ubuntu uses the DPKG-based APT package manager for installing, removing, as well as updating packages.

Linux Philosophy and Concepts

• Linux is an open-source OS developed for Intel x86-based personal computers and created by Linus Torvalds in 1991.
• It was later ported to other hardware platforms.
• It is re-licensed under the General Public License (GPL) by GNU.
• Combining the kernel with other system components from the GNU project, developers created complete systems called Linux Distributions in the mid-90s.
• Linux powers over 96% of the world's top web servers.
• The majority of smartphones use Linux via the Android system.
• Powers more than half of the servers on the Internet, more than 90% of the public cloud workload, and all of the world's most powerful supercomputers.
• It is consistently enhanced and maintained by a global network of developers.
• Technical skills, a desire to contribute, and the ability to collaborate are qualifications for participation.
• Linux borrows heavily from UNIX, but was written as a free and open-source alternative.
• In Linux, files are stored hierarchically, with the top node known as root or '/'.
• Processes, devices, as well as network devices are represented as file-like objects.
• Linux is a fully multitasking, multiuser OS with multiple built-in networking, as well as service processes called daemons.
• The Linux community consists of developers, system administrators, users, and vendors who connect through various forums like IRC, online communities, GitHub, GitLab, newsgroups, and community events.

Terminology

• Kernel is the glue between hardware and applications, acting as the brain of the OS, and can be found at kernel.org.
• Distribution is a collection of software/programs making up Linux-based OS.
• Boot Loader is a program that boots the OS (e.g., GRUB, ISOLINUX).
• Service is a program running as a background process (e.g., httpd, nfsd, ntpd, ftpd, named).
• Filesystem is a method for storing and organizing files (e.g., ext3, ext4, FAT, XFS, Btrfs).
• X Window System provides the standard toolkit and protocol for building graphical user interfaces.
• Desktop environment is a graphical user interface on top of OS (e.g., GNOME, KDE, Xfce, Fluxbox).
• The Linux kernel is the core of the OS.
• A full Linux distribution consists of the kernel plus software tools for file-related operations, user management, and software package management.
• Distributions provide compilers, debuggers, system libraries, graphical interfaces, and systems for installing and updating components.

Boot Process

• Procedure for initializing the system.
• Includes everything from switching on the computer to when the user interface is fully operational.
• BIOS (Basic Input/Output System) initializes the hardware and tests main memory, called POST (Power On Self Test).
• System control then passes from the BIOS to the boot loader, stored on a hard disk or SSD drive in the boot sector or EFI partition.
• Information on date, time, and peripherals are loaded from CMOS values.
• Common Linux boot loaders are GRUB, ISOLINUX, and DAS U-Boot.
• During Linux booting, the boot loader loads the kernel image and initial RAM disk into memory.
• For BIOS/MBR systems, the boot loader resides in the Master Boot Record (MBR) and examines the partition table to find a bootable partition.
• For EFI/UEFI systems, UEFI firmware reads Boot Manager data to determine which UEFI application to launch.
• The second stage boot loader resides under /boot, loads the OS kernel into RAM, and passes control to it.
• Kernels uncompress themselves, check hardware, and initialize device drivers.
• Initramfs filesystem image contains programs, as well as binary files to mount the root filesystem.
• It uses the udev system to locate device drivers.
• After locating device drivers the root filesystem is checked, then mounted, and the initramfs is cleared from RAM.
• The init program on the root filesystem (/sbin/init) is executed.
• Default command shell - bash (GNU Bourne Again Shell).

Linux Kernel

• Loaded to RAM by Boot loader, so that it can be directly used.
• The kernel initializes and configures the memory and hardware attached.
• Loads user space applications.

/sbin/init and Services

• The process after kernel sets up hardware and root filesystems and runs /sbin/init and becomes initial process to start the system.
• Most processes can trace back to init, except kernel processes started directly by kernel to manage internal OS details.
• Init is responsible for keeping the system running and shutting it down cleanly. Manages all non-kernel processes, cleans up after them, does same for background system services.
• Traditionally SysVinit was the process startup that uses conventions dated back to 1980s and System V Unix. Runs through runlevels with stopping and starting services.

Startup Alternatives

Upstart:

• Developed by Ubuntu, first included in 2006
• Adopted in Fedora 9(2008) and in RHEL 6 and its clones Systemd:
• Adopted by Fedora first(in 2011)
• Adopted by RHEL 7 and SUSE
• Replaced Ubuntu in 16.04 Features of systemd:
• Faster startup compared to older init methods by replacing serialized steps with parallelization.
• Replaces shell scripts with simpler config files about service startup and conditions.
• /sbin/init now points to /lib/systemd/systemd; so systemd takes over init process
• Systemd command is systemctl for the most basic tasks:
• Starting stopping, restarting services
• Enabling or disabling services from starting at system boot
• Checking status of service

Linux Filesystems

• A method to organize arbitrary collections of data in a human-usable form.
• Different types supported for Linux:Conventional disk filesystems(ext3, ext4, XFS, Btrfs, JFS, NTFS, vfat, exfat, etc.), flash storage systems(ubifs, jffs2, yaffs, etc.), database and special purpose filesystems(procfs, sysfs, tmpfs, squashfs, debugfs, fuse, etc.).
• Partitions- subsection of physical storage media and container in which filesystem resides. Can span more than 1 partition using symbolic links.
• Linux uses '/' character to separate paths, unlike windows that uses \ , and does not use drive letters

Filesystem Hierarchy Standard

• /bin/ Essential user command binaries.
• /boot/ Static files of the boot. loader.
• /dev/ Device files.
• /etc/ Host-specific system configuration.
• /home/ User home directories.
• /lib/ Essential shared libraries and kernel modules.
• /media/ Mount point for removable media
• /mnt/ Mount point for temporary mounted filesystems.
• /opt/ Add-on application software packages.
• /root/ is the Home directory for the root user.
• /sbin/ contains System binaries.
• /srv/ contains Data for services provided by this system.
• /tmp/ contains Temporary files.
• /usr/ contains Multi-user utilities, as well as applications
• /var/ contains Variable files.
• /proc/ Virtual filesystem documenting kernel and process status as text files
• All Linux Filesystems are case sensitive
• Core Utilities needed for system operations are placed in directories under /usr directory

Chosing Linux Distrobutions

• Server (RHEL/CentOS, Ubuntu Server, SLES/OpenSuse)
• Desktop(Ubuntu, Fedora, Debian, ArchLinux)
• Embedded(Yocto, Open Embedded, Android)
• Linux Distrobutions on removable media such as USB Drives, CDs or DVDs
• Installation process uses configuration files to specify installation options
• Kickstart file(RedHat)
• AutoYAST(SUSE) -Preseed(Debian)

Graphical Interface

CLI vs GUI

• CLI- uses programmed and commands, it is efficient and can quickly obtain more information
• GUI- uses graphical icons and screens

Desktop Environment is a session manager that maintains components of graphical session, a window manager for placement, window title-bars and movement and forms one with utilities

• Display manager started by running startx from command line, or manually like (gdm, kdm, xdm, etc)

X Window System

Loading the graphical desktop is the final step

• Service called Display manager tracks displays and loads X Server Apps - X clients
• A newer system, known as Wayland

GNOME- Desktop Environment with easy access GUI which has menu-based navigation

• -KDE, Unity, XCFE are alternatives gdm for GNOME and kdm for KDE as default Display Managers
• Tweaks- standard utility that allows installation by external parties with alt-f2 then typing in Keyboard Shortcuts, Locking- super+L or super +esc Viewing - Ctrl-1 and Ctrl-2 switches Icon and List formats, Ctrl-H shows Hidden files Open File Manager- type Nautilus
• Can access a specific directory through Crtl-L
• Text editors/viewers located in Accessories Submenu
• System Settings allows control of basic configuration options

Installing and Updating Software

-Linux distribution in the Package provides one piece of the system, including linux kernel.

• Debian pacakaging system(Ubuntu) RMPPacakkagi systems(Red hat)
• Deb packagaingdpkg= package Manager where you can install, etc •Unlike higher-level package management systems, it does not automatically download and install packages and satisfy their dependencies

RPM Package Manager

• RPM(Red hat package manager) -theother package mngmt system popular on Linux distribution and Fedora.
• The higher level-package manager differs between distribution and Red Hat family distributions while SuSEFamily
• The Linux allows users around the world to perform multiple tasks, such as searching for data, communicating through emails and online shopping, -Network applications that take advantage of the internet

web browsers

-Email, Streaming clients -Variety of web browsers both graphical and test base- the difference between and which one is which

Applications

 -Email Application, Sending, receiving and  reading message

• Most email clients use the Internet Message Access Protocol or the oder pop store Mail Store in remote -Many applications display HTML formatted emails Email app- ability of importing of address books

• Graphial and tests and evolution to display emails

Common Apps

• Other Graphic Utilities: Use of Filezilla, and Pidgin applications

• productivity tools- Writer- word Processing, Calc - SpreadSheets, Impress = Presentation -draw- Create and edit graphics and diagrams

• Multimedia Applications- sound Apps and Movie Apllications and MPlayer

###Command Line Operators

• Advantage of command line operatos such ad not GUI is incurred in Virtualany and everything tasks -implemented Scripts or for often used to forget task and series of procedures -sign in to remoter machines over, the the internet

• A terminal emulator program simulates standard alone terminals with a window on the Desktop example gnome Input Line- three elements- command option and argrument

Basic Command Like Utitliies

-Cat for Type outof a file to -Head and Taoil to show top and low lines of a file -.Man to Vew Documentation Sudo to provide user With Admin privileges when required

VIrtual Terminal

-VT are consol sessions, Entire display keyboard outside graphically environment and are called vt. and multiple terminals one remains visual

• switch Vt press Ctrl + function and call to restart that press sudo terminal 5 Tacl to Took for Fies backward and lell used to vew file becaus of the paging

• the opposites to tall if You want the last lines instead to view for files in order

Table: command line Utilies used to view file

_ Touch is often used to set and update access and change times of Files by Default

• Standard File Stream
• stdin keyboard stand and stderr
• Pies if the one command to or program into another for in as import

Command

-the data it should complete before beging it from another data -and no seed to gave output

• the core parts of Linux distributed and its addon software installed via Packagement System
• packages can depend on each other
• debilan use RPM as low packet

Chap 8: Finging Linux DOcumentation

• linux systems draw from a large of Documentation and waus to getting Help
• man pages are most often-used source of Linux Documentation with utilities.
• The man program -list of page to see by topic and then list that discuss that specific title -viewers to pages and how they all work together Info-

GNU Info System

-which Preffere to alternative then Manuel and support linked subsection from resembles many was -topics help for all arguments. -the topic viewed in info pages is Node for view all sections and item from links