learning-linux

learning-linux

This is the repository for the training Learning Linux

Instructor

Pierre-Yves Barriat

ACELI Training Sessions

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What is UNIX ?

• Operating System > Windows 10 (Microsoft), MacOSX (Apple), Android (Google), etc
• UNIX is a (family of) Operating System
• Invented by AT&T Bell Labs in late 60's
• Currently there are different versions and variants of UNIX > Solaris, AIX, HP-UX, etc.
• UNIX is not free or Open Source: "GNU is Not UNIX"

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What is Linux ?

• GNU (80's) is a free, open source version of the UNIX OS, but without the most important element: the kernel
• Linux kernel was developed in 1991 by Linus Torvalds, a Finnish graduate student
• The association GNU/Linux is an operating system (say just "Linux") and provides an alternative to commercial operating systems
• Linux exists without GNU (eg Android) : used to power a multitude of systems... from your phone to your smart fridge

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What is a Linux distribution ?

• Many versions of Linux

  Red Hat, Debian, Suse, etc

• But one common linux kernel: kernel is like an engine. A distribution is an actual car that hosts the engine

• Distributions differ from

  • the application/management layer
  • GUI (Graphical User Interface = desktop environment)
  • software packages
  • help-desk, support, language

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Why Linux ?

• Linux is free
• Linux is supported on older computers (perf & updates)
• Linux has many more free applications

Security: there are very few viruses for Linux Privacy: most Linux distributions don't collect your data at all Reliability: if you want to stop something, you really can Updates: package manager Customisation: you can make Linux look, feel and behave as you want it to Command Line Interface: faster & efficient

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Linux Statistics

• 47% of professional developers use Linux-based operating systems (Statista)
• Linux powers 39.2% of websites whose operating system is known (W3Techs)
• Linux powers 85% of smartphones (Hayden James)

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Why not Linux ?

1. Hardware compatibility (printers, etc)
2. Missing famous software (MS Office, Adobe, CAO, etc)
3. Gaming

Workarounds

1. Many devices "Linux compatible"
2. Emulation (eg virtualbox), online usage, alternatives (GIMP)
3. Difficult, but it exists emulation and Steam

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Distribution: why Ubuntu ?

• easy to install and easy to use
• easy to maintain and update
• useful applications
• looks nice
• wide variety of supported applications
• strong community support
• better driver support
• LTS and staging releases available as per user needs

get the latest Ubuntu LTS : ubuntu-22.04.2-desktop-amd64.iso

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Test Linux inside Windows: how ?

Using a virtual machine: test Linux without changing anything to your computer

You need to install a VM and then install the Linux inside

• Get a Virtual Machine: https://www.virtualbox.org/wiki/Downloads

  VirtualBox + Extension Pack

• Install Linux in a VM: Install Linux Inside Windows Using VirtualBox

  Step by Step Guide

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Linux GUI

A Linux distribution contains a display server, a window manager (manage windows, panel, menus, dash interfaces and core applications), and a desktop environment (eg status bars, drag-and-drop capabilities, etc)

These 3 items are bundled together to make what is known as a GUI environment

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Using Linux

Using Linux through a GUI environment is similar to Windows or MacOSX

Linux users do not install software the same way that Windows users do: Linux has a tool known as a package manager

A package manager provides a way to search for software, install software, keep the software up to date and remove the software

Similar to Google or Apple store

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Linux CLUI

Using Linux with GUI, it's already great ! Using CLUI = unlock the power of Linux !

Each Linux system contains a terminal

A terminal is where you enter Linux commands

It's called the Command Line User Interface

CLUI is one of the many strengths of Linux and can be more efficient than using the GUI

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Linux CLUI

• CLUI allows users to be independent of distros (or UNIX systems like OSX)
• CLUI saves system resources which are consumed by GUIs
• CLUI allows users to easily work at distance (SSH)
• CLUI allows developers to join together simple (and less simple) commands to do complex things and automate... whatever you want to

People tend to think command line is difficult. It's not.

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Linux Shell

A shell is a program that takes commands from the keyboard and gives them to the operating system to perform

The main function is to interpret your commands = language

The bash shell is one of several shells available for Linux

Learning the shell:

"When you are a child you use a computer by looking at the pictures. When you grow up, you learn to read and write"

It's more or less like SMSing to your PC, telling it what to do

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Linux Shell

Shells have some built-in commands

A shell also supports programming constructs, allowing complex commands to be built from smaller parts = scripts

Scripts can be saved as files to become new commands

many commands on a typical Linux system are scripts

An open terminal show you a PROMPT waiting for your commands

Commands can have options and parameters

All your commands are saved in a history

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Linux Shell Demo

Rename many files at once ?

mmv '*.JPG' '#1.jpg'

Download a youtube video ?

youtube-dl https://www.youtube.com/watch?v=G7KNmW9a75Y&ab_channel=MileyCyrusVEVO

Convert color pictures in BW at once ?

#!/bin/bash
for file in *.jpg
do
  convert ${file} -colorspace Gray "${file%.*}_bw.jpg"
  echo "${file}... converted"
done

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What you'll learn

• Navigating the File System

  Get up and running with the CLUI by navigating directories and files

• Viewing and Changing Files and Directories

  Learn to manipulate directories and files from the CLUI

• Configuring the Environment

  Learn to configure the environment using the CLUI

• Accessing Linux remotely

  Learn to use SSH (basics)

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Navigating the File System

A file system is a section of hard disk that has been allocated to contain files

it's arranged like hierarchical tree structure

Files are grouped in the directory structure

The top of the tree is called root and / is used to present the root

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Absolute paths

In the tree /users/usern/file1 is an absolute pathname

Relative paths

If you are already in the users directory, the relative pathname for file1 is usern/file1

• ~ (tilda) points to the user's home directory. Useful if you are logging into a workstation with many users. It's the default working directory when you log in. If you are user usern, then /users/usern/file1 is the same as ~/file1

• . refers to the current directory

• .. refers to the parent directory

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Basic commands

• ls : lists folders/files in a directory
• cd : change directory > use cd name to navigate to directory name
• pwd : print working directory. Prints the path of the current directory
• du : disk usage. Shows the disk usage of the current directory
• man : manual
  > use man name to bring up a manual entry for command or program called name

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Creation

• mkdir : use mkdir name to create a new directory named name in the current directory
• cp : use cp file1 file2 to create file2 which is a copy of file1 > can also use cp -r to copy whole directories
• mv : move = same as copy, but deletes the original file

Deletion

• rm : delete files ( cannot recover your files after removed them ! ) > can also use rm -rf to remove whole directories

Be careful : there is no trash in CLUI

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• tab is used for auto-complete > If a file/directory name was partly typed in, tab will auto-complete it

If there are multiple options, tab will auto-complete up to the point where the options branch and show you a list of possible options

• * is used as a wild card > rm blah* removes all files which start with blah: eg blah1, blah2, and blahblah would all be removed
  

using cp public/* private/ copies all files in a public directory into a private directory, and keeps all file names intact

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File permissions

Groups

Each file and directory has three user based permission groups

• owner :the owner permissions apply only the owner of the file or directory, they will not impact the actions of other users
• group : the group permissions apply only to the group that has been assigned to the file or directory, they will not effect the actions of other users
• all users : the all users permissions apply to all other users on the system, this is the permission group that you want to watch the most

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Types

Each file or directory has three basic permission types

• read : the read permission refers to a user's capability to read the contents of the file
• write : the write permission refer to a user's capability to write or modify a file or directory
• execute : the execute permission affects a user's capability to execute a file or view the contents of a directory

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The following command :

ls -l

gives :

1	2	3	4	5	6	7
-rwxr-xr-x	1	dupont	grpelic	3528	2022-08-04	file_1
drwxr-xr-x	3	dupont	grpelic	512	2022-01-02	dir_1
lrwxr-xr-x	2	dupont	grpelic	210	2020-12-16	short -> /data
-rw-------	1	dupont	grpelic	4587	2022-12-04	file_2

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Linux privileges

Linux has a robust permissions system: this is a very good thing, as it enables a clear separation of roles among users

Especially between the root user and your standard user

Sometimes, though, you might want your standard user to have some or all of root's privileges : this is accomplished with sudo

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Shell syntax rules

Shells use three "standard I/O streams"

• stdin is the standard input stream, which provides input to commands.
• stdout is the standard output stream, which displays output from commands.
• stderr is the standard error stream, which displays error output from commands.

Shell has several meta-characters and control operators

|, &, >, ; , etc.

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Environment

In a bash shell many things constitute your environment

• the form of your prompt
• your home directory and your working directory
• the name of your shell
• functions that you have defined
• etc.

Environment includes many variables that may have been set by bash or by you

Access the value of a variable by prefixing its name with $

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Environment variables

• USER : the name of the logged-in user
• UID : the numeric user id of the logged-in user
• HOME : the user's home directory (similar to ~ )
• PWD : the current working directory
• SHELL : the name of the shell

Set a shell variable : typing a name followed immediately by an equal sign ( = )

if the variable exists, you will modify it to assign the new value

You can use special files to control bash variables : $HOME/.bashrc

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Remote Linux Access

SSH (or Secure SHell) is a protocol used to securely log onto remote systems

the most common way to access remote Linux and Unix-like servers

VNC (or Virtual Network Computing) is a software that allows a personal computer's desktop environment to be run

Aside from bandwidth, latency and security issues (which can vary a bit), the big differences are the functionality

• VNC exports a whole session, desktop and all (GUI)
• SSH runs a single program (CLUI) and show its windows on your machine

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Remote Linux using SSH

You need:

• an access to the distant machine : login/password > or a login with SSH keys (with passphrase)
• the hostname or the IP address of the distant machine
• and (of course) a UNIX terminal

ssh -X pbarriat@coriolis.elic.ucl.ac.be

ssh -X -i ~/.ssh/id_rsa.ceci pbarriat@gwcism.cism.ucl.ac.be

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Remote Linux from Windows

Using a SSH client to reach a distant Linux Workstation

mobaXTerm is free and easy to use

allow you to test a Linux environmment but in CLUI only

Get a SSH client https://mobaxterm.mobatek.net/download-home-edition.html

How to use a SSH client https://support.ceci-hpc.be/doc/_contents/QuickStart/ConnectingToTheClusters/MobaXTerm.html

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Scripting

How to do a backup ?

• with Dropbox or Google Drive ?
• with a private cloud such as Nextcloud ?
• with an other drive and/or an external drive ?

Backup on external drive ?

• manually ?
• with Windows tools ?
• with external softwares ?

Why don't do that with a simple linux script ?

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Conclusions

Advantages of Linux	Disadvantages of Linux
Cost	Not easy to master ( CLUI only )
Security and robustness	Hardware compatibility issues ( sometimes )
Freedom	Not compatible with some Windows software
Software
Development

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Need to know more about available Linux applications ?

Check out the list of the best Linux software

Need help with bash scripting ?

• Bash Scripting Tutorial for Beginners
• Bash scripting cheatsheet

Need help with Ubuntu ?

The massive community is one of Ubuntu's biggest strengths

Visit https://askubuntu.com/ or https://answers.launchpad.net/