Reference Book: Linux Administration A Beginner's Guide
*Author * : Wale Soyinka
Linux: The operating system:-
- Linux is an open-source operating system; it contains a kernel, and that kernel is the heart of Linux. The kernel operates the hardware components (RAM, CPU, storage device, and input/output devices) and manages system resources, for example, files, processors, memory, devices, and networks.
- The kernel is a nontrivial program; it means complex, significant, and not easy to implement.
- Linux: All distros use different customized versions of the kernel, but core functionality is the same for all distros, such as file management, processing, and networking.
- Linux distro RHEL, Fedora, Debian, Ubuntu, CentOS, Arch...etc. Linux differentiates two categories. One is commercial (supported by vendor company distro longer release life cycle; it means support and update for a long year with a paid subscription); another one is uncommercial (free), managed by the open source community with a short year release.
- The open source (uncommercial) and commercial Linux distros are interconnected because commercial companies support free distros as testing grounds. Most Linux software is developed by independent contributors, not the company side.
kernel differences:-
Each company sells its own developed distro and customizes the kernel. The company says that its kernel is better than the others. Why say it is better than other kernels? Most of the company and vendor companies stay updated with patches that are posted on www.kernel.org, the "Linux Kernel Archives." However, the vendor company does not track the release of the single kernel version released on wwe.kernel.org; instead of applying the custom patches to it to run the kernel quality assurance process, it tells the production is ready to help the commercial customer; it makes them confident. Any exception that occurs on the kernel-related vendor team immediately takes the action and fixes the issue, so every vendor maintains its own patch maintenance. Every vendor makes its own market strategies in the traditional environment, and the distro is designed as per the user's requirements, like making the kernel version customizable for purposes such as desktop, server, and enterprise.
The GNU Public License:-
In 1980, Richard Stallman was the founder of the Free Software Movement and the initiator of the GNU Project.
Richard Stallman is quoted as saying:
“Free software” is a matter of liberty, not price. To understand the concept, you should think of “free” as in “free speech,” not as in “free beer.”
The main goal of giving away source code is freedom and flexibility. The user should have control over the software; the user cannot depend on the developer or officials. Open source's main goal is that anyone can modify and improve it. The advantage of open-source software is that it allows the community user with necessary skills to collaborate and add new features and contribute to improving software for the benefit of everyone.
The Gnu project is the GNU public license (GPL); it means any GPL software anyone can view the source code, edit, reconstruct, release the full source code, sell, and get profit, but one condition is the GPL editable version released under the GPL license. Other licenses are there, such as BSD and Apache, that have similar rules but differ in terms and redistribution. For the BSD license, anyone can change the source code and use it. You can hide that you made changes to keep it private from others, but GPL is not allowing this term. You must showcase what you modified in the software. You can see more related info from www.opensource.org.
Upstream and Downstream:-
Upstream is a source code of original project where the code is first developed , you take the code for open source project and modify it, original upstream means for example you buy the normal veg pizza in a pizza shop you gathered all ingrediencies info take it and make it new version chesses pizza include your ingrediency.
Downstream is modify version of code ,the project use, modify, extend the upstream code , you can take the opensource project build your own version your project is downstream. Key points is changes made upstream it affect downstream project for example Linux kernel upstream source code for the many Linux distro, ubuntu, fedora ,downstream project do not go back the upstream.
Single Users vs. Multiple Users vs. Network Users
- window was originally designed purpose is one time one user can work in window . two people can not work with co incidentally at a time .Linux is support multiuser environment ,it means two user work single time multiuser environment in Linux.
- Network user and server client model for both Linux and windows provide services like database example sql, mysql, postgresql over a network ,from windows designed for client and server communication with restrictive and Linux flexible ,any program run remotely with admin permission.
The Monolithic Kernel and the Micro-Kernel:-
The kernel has three different types of use in operating systems. One is a monolithic kernel, everything inside of a single program, like Unix and Linux. The second one is a micro-kernel, a limited core set of services needed to implement the operating system example window. The third one is a hybrid; it combines the first two kernels. The current industry uses a Windows hybrid kernel. The Windows kernel provides a small set of services that interface with other executive services like process and I/O management.
Domains and Active Directory:-
- AD is a centralized device; it manages authentication and authorization for the domain. The domain synchronization model means that the domain controller checks everything for up-to-date information. DNS style, It means following the root domain and child domain architecture; for example, abc.com is the root domain, and it. ABC.com and sales.ABC.com as child domains; each domain maintains its own user and computer, but it is part of the root domain network.-
- Linux does not have tightly coupled (components do not depend on each other directory) authentication/authorization. Linux handles authentication used for the PAM pluggable authentication module; it means multiple authentication methods follow. Name resolution libraries help Linux find and verify user and group information from different sources, like local files, LDAP, and NIS.-
- Authentication option is linux, flat files basic authentications using /etc/passwd and /etc/shadow, NIC used to older network for centralized authentication ,LDAP (Lightweight Directory Access Protocol) work like AD but is open source, Kerberos secure authentication using tickets, Samba and Ad it allows to authenticate against windows domain.
