Linux Foundation Series

Linux – The Operating System

• RedHat Linux, Ubuntu, Centos, SUSE etc are called as distributions.
• Distribution is Linux + software suite of applications,developer tools
• In this essence Linux is core of the operating system: kernel

Layers of Abstraction in Linux

• General Linux System Organization
• Layers are
  • Hardware
  • Kernel
  • User Process
• Kernel is in charge for managing
  • Processes
  • Memory
  • Device Drivers
  • System Calls
    • fork
    • exec
• User Space:
  • Kernel allocates memory for user processes and this is called as userspace.
  • User: A user is an entity that can run processes and own files.

Shell and Terminal

• when we speak of the commandline we are referring to shell. Shell is a program takes commands and passes them to OS to carry out.
• Almost all the distributions a shell program called as bash is supplied.
• To interact with shell we need a terminal

Creating Linux Instances on the cloud

• Refer Here for setting up the softwares
• Refer Here for creating a linux ec2 instance in aws
• Refer Here for creating a linux azure vm
• Prerequisities
  • Softwares
    • Git Bash
    • Visual Studio Code
  • One free tier cloud account (AWS/Azure)
• Linux Distributions
  • Ubuntu 18
  • Centos 7
• Lets create a linux instance and login into that

Standard Input and Standard Output

• Linux Processes use I/O streams to read and write data.
• Streams are very flexible, the source of input stream can be a file, device or it can be even the output stream of other process

Linux Commands

• In the shell prompt we generally execute commands. Lets execute some simple commands

date
cal

• Basic command syntax

<command> <args>
echo hello

• Arguments of two types
  • Positional arguments:

  <command> <arg1> <arg2> ...
  cp 1.txt 2.txt
  

  • Named arguments

  <command> --<argname> <argumentvalue>
  ping -c 4 google.com 
  

• ls: this command is used to list the contents of the directory

ls
ls -a

• touch: this command creates an empty file

touch 2.txt

• cp: this command copies files

cp file1 file2

• mv: this command moves (rename) the files
• rm
• echo

Linux directory hierarchy

• Linux directory
• / => root directory
• /bin => Binaries and other executables
• /etc => system configuration files
• /home => home directories
• /opt => optional or third party softwares
• /tmp => Temporary space
• /usr => User related programs
• /var => variable data, log
• experiment with mkdir, rmdir, less, file, head, tail, exit

Environment and Shell variables

• Shell variables: Shell can temporarily store variables called as shell variables

<VAR-NAME>=<value>
TOPIC=linux
To access variable use $
echo $TOPIC

• Environmental variable: This is also like shell variable, but its not specific to the shell.

export <variable>

• There is one important environmental variable which is PATH. PATH variable will inform linux to find the commands

echo $PATH

Using Text Editors

• Every linux generally has a text editor which is vim.
• To learn using vim please refer here
• Other editor is nano