edu-python-course · shorodilov · Jan 25, 2024 · Jan 25, 2024 · Jan 25, 2024 · Jan 25, 2024
diff --git a/assets/img/linux-distros-map.png b/assets/img/linux-distros-map.png
diff --git a/assets/img/linux-distros-tree.svg b/assets/img/linux-distros-tree.svg
diff --git a/assets/img/linux-fs-layout.png b/assets/img/linux-fs-layout.png
diff --git a/pyproject.toml b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "python-course"
-version = "2023.11.dev"
+version = "2024.01-dev"
 description = "Python training course materials"
 license = "MIT"
 authors = [

diff --git a/src/appx/busybox.txt b/src/appx/busybox.txt
@@ -0,0 +1,3 @@
+###############################################################################
+                               BusyBox Commands
+###############################################################################
diff --git a/src/index.txt b/src/index.txt
@@ -33,6 +33,7 @@
         appx/wtk
         spec/blog/index
         spec/libms/index
+        appx/busybox
 
 .. rubric:: References
 

diff --git a/src/linux/commands.txt b/src/linux/commands.txt
@@ -0,0 +1,95 @@
+*******************************************************************************
+                                   Commands
+*******************************************************************************
+
+A computer's operation, no matter which operating system it is running, can be
+loosely described in three steps:
+
+#.  The computer waits for user input
+#.  The user selects a command and enters it via keyboard or mouse
+#.  The computer executes the command
+
+In a Linux system, the shell displays a "prompt", meaning that commands can be
+entered. This prompt usually consists of a user and host (computer) name, the
+current directory, and a final character:
+
+::
+
+    user@host: /home/user >
+
+Command structure
+=================
+
+A command is essentially a sequence of characters which is ends with a press
+of the **enter** key and is subsequently evaluated by the shell. Many commands
+are vaguely inspired by the English language and form part of a dedicated
+"command language". Commands in this language must follow certain rules,
+a "syntax", for the shell to be able to interpret them.
+
+To interpret a command line, the shell first tries to divide the line into
+words. Just like in real life, words are separated by spaces. The first word
+on a line is usually the actual command. All other words on the line are
+parameters that explain what is wanted in more detail.
+
+Parameters starting with a dash (``-``) are called **options**.
+These are usually optional -- the details depend on the command in question.
+They are "switches" that allow certain aspects of the command to be switched
+on or off. If you want to pass several options to a command, they can be
+accumulated behind a single dash, i.e. the options sequence ``-a -l -F``
+corresponds to ``-alF``. Many programs have more options that can be
+conveniently mapped to single characters or support *long options* for
+readability (frequently in addition to equivalent single-character options).
+Long options most often start with two dashes and cannot be accumulated:
+``--foo --bar --foobar``.
+
+Parameters with no leading dash are called **arguments**. These are often the
+names of files that the command should process.
+
+The general command structure can be displayed as follows:
+
+:command: what to do?
+:options: how to do it?
+:arguments: what to do it with?
+
+Internal and external commands
+------------------------------
+
+In shells, there are essentially two kinds of commands:
+
+-   **Internal commands**
+
+    These commands are made available by the shell itself.
+    The Bourne-again shell contains approximately 30 such commands,
+    which can be executed very quickly. Some commands (such as ``exit`` or
+    ``cd``) alter the state of the shell itself and cannot be provided
+    externally.
+
+-   **External commands**
+
+    The shell does not execute these commands by itself but launches executable
+    files, which within the file system are found in directories like */bin* or
+    */usr/bin*. As a user, you can provide your own programs, which the shell
+    will execute like other external commands.
+
+What is the shell?
+==================
+
+All kinds of definitions are available, ranging from the simple comparison that
+"the shell is the steering wheel of the car", to the vague definition in the
+Bash manual which says that "bash is an sh-compatible command language
+interpreter", or an even more obscure expression, "a shell manages the
+interaction between the system and its users".
+
+A shell can best be compared with a way of talking to the computer, a language.
+Most users do know that other language, the point-and-click language of the
+desktop. But in that language the computer is leading the conversation, while
+the user has the passive role of picking tasks from the ones presented. It is
+very difficult for a programmer to include all options and possible uses of
+a command in the GUI-format. Thus, GUIs are almost always less capable than
+the command or commands that form the backend.
+
+The shell, on the other hand, is an advanced way of communicating with the
+system, because it allows for two-way conversation and talking initiative.
+
+.. todo: get most used commands from appendix:
+         pwd, cd, ls, mkdir, touch, more, less, head, tail
diff --git a/src/linux/filesys.txt b/src/linux/filesys.txt
@@ -0,0 +1,86 @@
+*******************************************************************************
+                        File system and file management
+*******************************************************************************
+
+Files
+=====
+
+A simple description of the UNIX system, also applicable to Linux, is this:
+
+    "On a UNIX system, everything is a file; if something is not a file,
+    it is a process"
+
+This statement is true because there are special files that are more that just
+files (named pipes and sockets for instance), but to keep things simple, saying
+that everything is a file is an acceptable generalization. A Linux system, just
+like UNIX, makes no difference between a file and a directory, since
+a directory is just a file containing names of other files. Programs, services,
+texts, images, and so forth, are all files. Input and output devices, and
+generally all devices, are considered to be files, according to the system.
+
+.. rubric:: Sorts of files
+
+:regular files:
+    most files are just *files*, called *regular* files; they contain normal
+    data, for example text files, executable files or programs, input or
+    output from a program and so on.
+
+:directories:
+    files that are lists of other files.
+
+:special files:
+    the mechanism used for input and output.
+    Most special files are in ``/dev``.
+
+:links:
+    a system to make a file or directory visible in multiple parts of
+    the system's file tree.
+
+:sockets:
+    a special file type, similar to TCP/IP sockets, providing inter-process
+    networking protected by the file system's access control.
+
+:named pipes:
+    act more or less like sockets and form a way for processes to communicate
+    with each other, without using network socket semantic.
+
+The ``-l`` option to ``ls`` display the file type, using the first character
+of each input line:
+
++--------+--------------+
+| Symbol | Meaning      |
++========+==============+
+| ``-``  | Regular file |
++--------+--------------+
+| ``d``  | Directory    |
++--------+--------------+
+| ``l``  | Link         |
++--------+--------------+
+| ``c``  | Special file |
++--------+--------------+
+| ``s``  | Socket       |
++--------+--------------+
+| ``p``  | Named pipe   |
++--------+--------------+
+| ``b``  | Block device |
++--------+--------------+
+
+Linux file system layout
+========================
+
+For convenience, the Linux file system is usually thought of in a tree
+structure.
+
+.. figure:: /../assets/img/linux-fs-layout.png
+    :align: center
+
+    RedHat system layout
+
+The tree of the file system starts at the trunk or *slash*, indicated by
+a forward slash (``/``). This directory, containing all underlying directories
+and files, is also called the *root directory* or the *root* of the file
+system.
+
+Directories that are only one level below the root directory are often preceded
+by a slash, to indicate their position and prevent confusion with other
+directories that could have the same name.
diff --git a/src/linux/index.txt b/src/linux/index.txt
@@ -3,17 +3,133 @@
     :author: Serhii Horodilov
     :keywords: linux, basics, index
 
-.. todo
-
-.. attention:: Page is under construction
-
-    .. figure:: /../assets/img/construction.svg
-        :figwidth: 250
-        :align: center
-
 ###############################################################################
                              Linux Basics
 ###############################################################################
 
+Linux is a powerful, open-source operating system widely used in various
+domains, from embedded systems to supercomputers. It is known for its
+stability, security, and flexibility, making it a preferred choice for
+developers, especially in server environments.
+
+.. rubric:: What is an Operating System?
+
+.. _os_overview:
+
+An operating system (OS) is the primary software that manages all the hardware
+and other software on a computer.
+It acts as an intermediary between the physical hardware and the user
+applications, providing essential services needed for the applications
+to execute.
+
+.. _os_functions:
+
+The operating system is the fundamental suite of software on a device that
+keeps everything together. It interacts with the device's hardware components,
+handling everything from input devices like keyboards and mice to output
+devices like displays and printers. The OS sits between the applications you
+run and the hardware, using hardware drivers as an interface between them.
+For instance, when an application wants to print a document, it hands off
+the task to the OS. The OS then sends instructions to the printer using printer
+drivers to send the correct signals. The printing application does not need
+to understand the specifics of the printer or how it works.
+The OS handles the details.
+
+OS includes a variety of software components such as system services,
+libraries, and :abbr:`APIs (Application Programming Interfaces)` that
+developers use to write applications that run on the OS.
+
+The OS also manages multitasking, allocating hardware resources among multiple
+running programs. It controls which processes are running, distributing them
+among various CPUs if you have a computer with multiple processors or cores,
+allowing multiple processes to run in parallel. It also manages the system's
+internal memory, allocating memory among running applications.
+
+When we say "computers" run operating systems, we don't just mean traditional
+desktop PCs and laptops. Your smartphone is a computer, as are tablets,
+smart TVs, gaming consoles, smartwatches, and Wi-Fi routers. An Amazon Echo or
+Google Home is a computer device running under the management of an operating
+system.
+
+Familiar desktop operating systems include Microsoft Windows, Apple MacOS,
+Google's Chrome OS, and Linux. The primary operating systems for smartphones
+are Apple's iOS and Google's Android.
+
+Other devices, like a Wi-Fi router, may run "embedded operating systems".
+These are specialized operating systems with fewer features than a typical
+operating system, designed specifically for a single task - like operating
+a Wi-Fi router, navigating, or controlling an ATM.
+
+Operating systems also include other software, including the user interface,
+which allows people to interact with the device. This could be the desktop on
+a PC, the touch interface on a phone, or the voice interface on a digital
+assistant.
+
+The operating system is a large piece of software made up of many different
+applications and processes. The line between what is the operating system and
+what is a program can sometimes be a bit blurred.
+There isn't a strict official definition of an operating system.
+
+For instance, in Windows, the File Explorer application is an integral part of
+the Windows operating system -- it even handles drawing your user interface --
+and an application running on that operating system.
+
+.. rubric:: Linux pros
+
+-   Linux is free
+-   Linux is portable
+-   Linux was made to keep on running
+-   Linux is secure and versatile
+-   Linux is scalable
+-   The Linux OS and most Linux applications have very short debug-times
+
+.. rubric:: Linux cons
+
+-   There are far too many different distributions
+-   Linux is not very friendly and confusing for beginners
+
+.. rubric:: Linux -- the Kernel and distributions
+
+The core of an operating system is the kernel.
+
+At a low level, the "kernel" is the core computer program at the base of your
+operating system. This single program is one of the first things loaded when
+your operating system starts. It handles memory allocation, converts software
+functions into instructions for your computer's CPU, and processes input and
+output from hardware devices. The kernel typically runs in an isolated area
+to prevent it from being used by other software on your computer.
+The kernel of an operating system is crucial, but it's just one part of
+the operating system.
+
+Strictly speaking, the name **"Linux"** only applies to the operating system
+kernel, which performs the actual operating system tasks. It takes care of
+elementary functions like memory and process management and hardware control.
+Application programs must call upon the kernel to, e.g. access files on disk.
+
+However, Linux is still often referred to as an operating system.
+
+To accomplish useful work, a multitude of system and application programs,
+libraries, documentation etc. is necessary. "Distributions" are nothing but
+up-to-date selections of these together with special programs (usually tools
+for installation and maintenance) provided by companies or other organisations,
+possibly together with other services such as support, documentation, or
+updates. Distributions differ mostly in the selection of software they offer,
+their administration tools, extra services, and price.
+
+.. figure:: /../assets/img/linux-distros-tree.svg
+    :align: center
+
+    Linux distros tree
+
+.. figure:: /../assets/img/linux-distros-map.png
+    :align: center
+
 .. toctree::
     :name: linux
+    :caption: Contents
+
+    commands
+    filesys
+    users
+    ssh
+    symlinks
diff --git a/src/linux/ssh.txt b/src/linux/ssh.txt
@@ -0,0 +1,11 @@
+*******************************************************************************
+                              (SSH) Secure Shell
+*******************************************************************************
+
+The :abbr:`SSH (Secure Shell)` Protocol is a network protocol for secure data
+communication and remote command execution. It is a cryptographic network
+protocol for operating network services securely over an unsecured network. Its
+most notable applications are remote login and command-line execution.
+
+SSH uses public-key cryptographic to authenticate the remote computer and allow
+it to authenticate the user, if necessary.
diff --git a/src/linux/symlinks.txt b/src/linux/symlinks.txt
@@ -0,0 +1,3 @@
+*******************************************************************************
+                                   Symlinks
+*******************************************************************************
diff --git a/src/linux/users.txt b/src/linux/users.txt
@@ -0,0 +1,3 @@
+*******************************************************************************
+                             Users and Permissions
+*******************************************************************************
diff --git a/src/refs.bib b/src/refs.bib
@@ -225,3 +225,29 @@ @misc{medium:db-acid-cap
     date = {2017.1.12},
     url = {https://cinish.medium.com/database-acid-cap-isolation-levels-371b7e06a112}
 }
+
+@manual{linux-intro,
+    title = {Introduction to Linux. A hands on guide},
+    author = {Machtelt Garrels},
+}
+
+@manual{linux-tutorial,
+    title = {Linux Tutorial},
+    author = {Jon Wakelin and Liam Gretton and Gary Gilchrist and Teri Forey},
+}
+
+@manual{linux-grd1-manual,
+    title = {Introduction to Linux for Users and Administrators},
+    author = {Tobias Elsner and Anselm Lingnau},
+    editor = {Anselm Lingnau},
+}
+
+@misc{busybox,
+    title = {BusyBox - Command Help},
+    url = {https://busybox.net/downloads/BusyBox.html},
+}
+
+@misc{curl,
+    title = {command line tool and library for transferring data with URLs},
+    url = {https://curl.se/},
+}