Linux Architecture
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Video Transcription
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>> Welcome back to cyber Linux fundamentals
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for security practitioners.
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I am your instructor, Corey Holzer.
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In this lesson, we'll be taking
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a look at Linux's architecture.
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Let's get started. We have
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two objectives for this lesson.
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First, we'll identify the key elements
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of the Linux architecture.
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Second, once we have identified them,
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we'll discuss their roles and how they work together
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to provide you with a functioning operating system.
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In broad terms, Linux consists
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of seven categories of components.
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Some of these are unique, as you will see,
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but others are categories
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consisting of multiple examples.
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I'd startup the first element loading
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into memories of the bootloader.
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It presents options to the user
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as to how they will start Linux.
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The brains and resource manager for
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the operating system is known as the OS kernel.
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The next component of Linux are services.
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There are a plethora of them,
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including those which you actively interact with like
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a web server or remote access functionality,
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and those that run in the background
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like network services,
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allowing the host to communicate with a larger network.
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The shell is the primary user interface and
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something you will become very
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familiar with throughout this course.
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The graphics are commonly referred to as X is
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the foundation for the graphical user interface
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that you can also interact with.
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You interact with it through the desktop environment.
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The desktop environment determines
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how the GUI appears to the user.
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It tells the graphic server how to draw
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the windows and the appearance
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of the mouse pointers, et cetera.
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Applications are just those you find in Windows,
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they are productivity tools provided to
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you for the performance of tasks.
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When you press the power button on every computer,
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it goes through something called the
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power-on self-test or POST.
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This simply ensures that everything
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works as expected from the hardware perspective.
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The only time you really know
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there's an issue is when you hear
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an atypical series of
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beeps and or an error on the screen.
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Once the post complete successfully,
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the bootloader is the first element
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of Linux loaded into memory.
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It triggers the loading of the actual operating system,
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whether automatically or by prompting the user
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to choose from one of multiple boot options.
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These options can change configurations for
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the operating system based on each option.
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These can also be password protected.
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In most cases, particularly on servers,
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there will be a default boot option
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that will load automatically.
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If there wasn't a default boot option,
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then the computer would sit waiting for input
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and the operating system would never load.
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Once the bootloader completes its function,
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the part of the operating system that functions
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closest to the hardware is the kernel.
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The kernel acts as a manager handling
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the allocation of all the systems resources.
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It prioritizes access to the CPU,
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RAM and storage, impacting
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performance and ensuring
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all requests are handled properly.
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A host, that cannot interact with other hosts in
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an environment for all intents and purposes is useless.
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Services running on a host not only
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provide utility to users and other hosts,
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but they also manage
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connectivity with the network and other hosts on it.
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Services you more commonly
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interact with or services like DNS,
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web services via Apache or Engine X.
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Databases like MySQL or Postgres.
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File services allow us to mount shares through
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SMB or download files through FTP or SFTP.
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In many cases these are
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active i.e we choose to go to a website,
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but some are passive.
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i.e, translating the website
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URL into an IP address is the job of DNS.
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Module 3, we'll focus extensively on the shell,
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but at this juncture is
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important to understand that the shell was
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the original interface or means of
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interaction between the user and the computer.
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Or user provides instructions or commands to
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the computer via the shell and the host response.
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Today's operating systems employ
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a graphical user interface,
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which tends to be more
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user-friendly and far less cryptic.
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But the GUI is just more user-friendly for
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doing things that can be
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done on the command line as well.
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The graphic server functions as the middleware
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between the operating system and the desktop environment.
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It provides the foundations for
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the graphical user interface or GUI.
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All desktop environments receive details about
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the size of Windows and their position from X,
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and they then skin them and
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present them to the users on-screen.
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Linux has many different desktop environments,
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and while they all have similar components like Windows,
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tab views, et cetera,
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they can look very different from one another.
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This is because the desktop environment
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receives information about the basic components from
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the graphical server and then skins
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those components in the manner
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prescribed by the desktops design.
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Think of it like this.
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Every house has walls,
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windows, doors, support structures, et cetera.
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But each house is relatively
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unique in terms of its design and organization.
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Applications are tools we use to perform tasks.
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The most common ones you are probably familiar with are
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the productivity tools like Microsoft Office,
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calculator applications, web browsers, et cetera.
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It is no different in Linux.
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One thing that is important to understand is
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the fact that many GUI applications in
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Linux are just a front end
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that communicates with the command line tools.
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I will discuss this concept more in a future lesson,
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but it is an important concept to be familiar with now.
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In summary, we covered
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two areas of discussion in this lesson.
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First, we identified the seven key elements of
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categories that comprise Linux architecture.
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Second, we outlined the roles
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of each of these elements and
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how they interact with one another to
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provide functionality to the user.
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Thank you for joining me for this lesson.
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I look forward to seeing you in the next one.
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Linux OS Structure
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Useful Commands and How to Employ Them: Part 1
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Useful Commands and How to Employ Them: Part 2
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Using Pipes and Redirections on the Command Line
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