Linux

Contents

• What is Linux?
• Who uses it?
• Architecture
• Directory Structure
• Shell
• Commands

Linux

• Family of free and open-source software operating systems built around the Linux kernel (Fedora, Ubuntu, Red Hat etc.)
• Best-known and most-used open source operating system​ kernel
• History of Linux
  • Created by Linus Torvalds in 1991
  • Linux is modelled *after* Unix, it is not derived *from* Unix.
  • Unix for mainframes, Linux for PCs.

Who uses it?

• Almost every Big company i.e. Facebook, Amazon, Google, eBay etc.
• 95% of supercomputers
• 75% stock exchange
• Your mobiles etc.

Architecture

Kernel

• The central part of an operating system
• manages the operations of the computer and the hardware - most notably memory and CPU time.
• thought of as the program which controls all other programs on the computer
• There are two types of kernels:
  • A microkernel, which only contains basic functionality;
  • A monolithic kernel, which contains many device drivers.

Shell

• The shell accepts human readable commands and translates them into something the kernel can read and process.
• bash(Bourne Again shell), ksh, tcsh and zsh
• Terminal - program that opens a window and lets you interact with the shell.

• Shell Prompt

  There are various ways to get shell access:

  • Terminal -  X Terminal (XTerm), Gnome Terminal (GTerm), or KDE Terminal (KTerm) application.

  • Connect via secure shell (SSH) 

Basic Command Line Editing

• CTRL + L : Clear the screen.
• CTRL + W : Delete the word starting at cursor.
• CTRL + U : Clear the line i.e. Delete all words from command line.
• Up and Down arrow keys : Recall commands (see command history).
• Tab : Auto-complete files, directory, command names and much more.
• CTRL + R : Search through previously used commands (see command history)
• CTRL + C : Cancel currently running commands.
• CTRL + T : Swap the last two characters before the cursor.
• ESC + T : Swap the last two words before the cursor.
• CTRL + H : Delete the letter starting at cursor.

Users and Permissions

• Linux is a multi-user operating system
• User in the system is uniquely identified by a numerical number called the UID
• The root is superuser - has all rights to all files, system services, and softwares.
• Permissions - needs to protect users from each other
• You can create user groups to manage accesses
• Permissions: Read - Write - Execute

Sudo

• "Superuser do"
• Running commands with root user permissions
• sudo allows a permitted user to execute a command as another user, according to specifications in the /etc/sudoers file.
• sudo requires that users authenticate themselves with a password
• sudo can log both successful and unsuccessful attempts
• To edit the sudoers file, use the visudo command.
• Once a user has been authenticated, a timestamp is recorded and the user may use sudo without a password for a short period of time
• Use: prepend to any command

Basic Commands

• pwd - To know which directory you are in
• Is - to know what files are in the directory you are in. You can see all the hidden files by using the command “ls -a”
• cd - Use the "cd" command to go to a directory
• mkdir - create a folder or a directory
• rm - to delete files and directories. Use “-r” option to delete a directory
• touch - used to create a file
• cp - copy files. It takes two arguments: The first is the location of the file to be copied, the second is where to copy
• mv - Use the mv command to move files through the command line. We can also use the mv command to rename a file.

Intermediate Commands

• echo - helps us move some data, usually text into a file
• cat - Use the cat command to display the contents of a file. It is usually used to easily view programs.
• df - Use the df command to see the available disk space in each of the partitions in your system.
• du - Use du to know the disk usage of a file in your system. If you want to know the disk usage for a particular folder or file in Linux
• tar - Use tar to work with tarballs (or files compressed in a tarball archive) in the Linux command line.
• zip, unzip - Use zip to compress files into a zip archive, and unzip to extract files from a zip archive.
• chmod - Use chmod to make a file executable and to change the permissions granted to it in Linux.

Ubuntu

• Free and open source operating system and Linux distribution based on Debian
• Ubuntu is offered in three official editions:
  • Ubuntu Desktop: for Personal computers
  • Ubuntu Server: for servers and the cloud
  • Ubuntu Core: for Internet of things devices. 
• PPA: A Personal Package Archive (PPA) is a software repository for uploading source packages to be built and published as an Advanced Packaging Tool (APT) repository by Launchpad(web application that allows users to develop and maintain software).
• APT - works with core libraries to handle the installation and removal of software on Debian, Ubuntu

Package managing

• apt: Use apt to work with packages in the Linux command line. Use apt-get to install packages.
• This requires root privileges, so use the sudo command with it.
• To install - sudo apt-get install ...
• sudo apt-get update - update your repository each time you try to install a new package.
• You can upgrade the system by typing “sudo apt-get upgrade”

Directory Structure

Questions?

References

• https://www.thegeekstuff.com/2010/09/linux-file-system-structure
• https://thegeeksalive.com/linux-directory-structure-explained/
• https://en.wikipedia.org/wiki/Ubuntu_(operating_system
• https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard
• https://www.computerhope.com/unix/sudo.htm
• https://diyhacking.com/linux-commands-for-beginners/​

Thank You