krishnaprasadkv / Linux-Commands

Handy commands for Linux

Linux Basics

Overview

• What is Operating System ?
  Operating system is an interface between user and the computer hardware. The hardware of the computer cannot understand the human readable language as it works on binaries i.e. 0's and 1's. Also it is very tough for humans to understand the binary language, in such case we need an interface which can translate human language to hardware and vice-versa for effective communication.

• Types of Operating System:

  • Single User - Single Tasking Operating System
  • Single User - Multitasking Operating System
  • Multi User - Multitasking Operating System

Linux Architecture

• The architecture of UNIX can be divided into Four levels of functionality, as shown in Figure .

• Hardware
  Hardware consists of all physical devices attached to the System.
  Example:- Hard disk drive, RAM, Motherboard, CPU etc.

• Kernel
  kernel is the core component for any (Linux) operating system which directly interacts with the hardware. it schedules tasks, manages resources, and controls security.

  • Different types of the kernel are:
    • Monolithic Kernel
    • Hybrid kernels
    • Exo kernels
    • Micro kernels

• Shell
  Shell is the interface which takes input from users and sends instructions to the Kernel, Also takes the output from Kernel and send the result back to output user and starting applications.

  • Types of shells are classified into four:
    • Korn shell
    • Bourne shell
    • C shell

• Utilities
  Utilities provides the functionalities of an operating system to the users.

Linux File System Hierarchy

Path	Description
/	It is parent directory for all other directories.(root directory)
/root	It is home directory for root user and it provides working environment for root user
/home	It is home directory for other users and it provide working environment for other users
/boot	It contains bootable files for Linux. Like GRUB (GRand Unified Boot loader) boot.ini, ntldr
/etc	It contains all configuration files. Like User info /etc/passwd
/usr	By default softwares are installed in /usr directory
/opt	It is optional directory for /usr and it contains third party softwares.
/bin	It contains commands used by all users(Binary files)
/sbin	It contains commands used by only Super User (root)
/dev	It contains device file like hard disk /dev/hda
/proc	It contain process files and data are not permanent, they keep changing like information of CPU /proc/cpuinfo
/var	It is containing variable data like mails, log files
/mnt	It is default mount point for any partition. It is empty by default
/media	It contains all of removable media like CD-ROM, pen drive
/lib	It contains library files which are used by OS. Library files in Linux are shared object files

Commands

• Basic Commands

  • Overview
  • pwd
  • man
  • clear
  • echo
  • whoami
  • hostname
  • uptime
  • date
  • cal
  • id
  • last
  • touch
  • cat
  • mkdir
  • ls
  • cp
  • mv
  • rmdir
  • rm
  • cd
  • history
  • grep
  • find
  • ping
  • df
  • wget
  • ifconfig
  • du
  • free
  • top
  • kill
  • ps
  • groupadd
  • useradd
  • userdel
  • usermod

• LS Command

  • Overview
  • Working with ls command

• Filter Commands

  • Overview
  • less
  • more
  • head
  • tail
  • sort
  • cut
  • sed

• GREP Command

  • Overview
  • Working with grep command

• Find Command

  • Overview
  • Working with find command

• File Permissions

  • Overview
  • Absolute Mode
  • Symbolic Mode

• Changing Ownership and Group

  • Overview
  • Change the owner of a file
  • Change the owner and group of a File
  • Change the group of a file
  • Change symbolic links ownership
  • Recursively change the file ownership

• VI Editor

  • Overview
  • Insert Mode
  • Command Mode
  • Extended Mode

• Linux Links

  • Overview
  • Types of Links
  • Difference between soft link and hard link
  • Working with Links

• Managing Process

  • Overview
  • Types of processes
  • Working with ps command

• Signals In Linux

  • Overview
  • Few Important Signals
  • Using most common signals
  • Working with signals
  • Setting up the priority of a process
  • Working with renice

• Top Command

  • Overview
  • Top Command Explanation
  • Top Command Task's Property
  • Working With Top Command

• User Administration

  • Overview
  • Types of Users In Linux
  • Working with User Administration Commands
  • Creating a User
  • Assigning Password To The User
  • Modifying the User's Attribute
  • Locking and Unlocking a User Account
  • Changing the Password parameters
  • Deleting a User

• Group Administration

  • Overview
  • Working with Group Administration Commands
  • Creating a Group
  • Modifying the Properties of the Group
  • Adding and Removing Members to a Group