Basics of Linux Terminal Commands

 

What is Linux?

Linux is one of the most used operating system for programmers.  Most of them prefer Linux over other operating systems due to its versatility, power, security, and speed. Linux comprises several different pieces

·         Bootloader

·         Kernel

·         Init system

·         Daemons

·         Graphical server

·         Desktop environment

·         Application

We will basically focus on Kernel here

What is Kernel?

This is the one piece of the whole that is actually called Linux. The kernel is the core of the system and manages the CPU, memory, and peripheral devices. The kernel is the lowest level of the OS.

 

What is Linux Terminal/Console?

The Linux console is a system console internal to the Linux kernel. The Linux console provides a way for the kernel and other processes to send text output to the user and to receive text input from the user. The user typically enters text with a computer keyboard and reads the output text on a computer monitor.

 

BASIC LINUX COMMANDS

COMMAND	PURPOSE
Ctrl + l / clear	Clears the screen
uname	Gives the environment name of the system
q	quit
man	Gives the manual of a specific command
uptime	Gives uptime details of the system (active time)
cd	change directory
cd..	one directory back
cd	Shift to the parent directory
pwd	Gives the present working directory
ls	List of files
mkdir	Make a directory within the present location
ls – l / ll	A long list of files in the directory
alias	Creates aliases
ls -a	Listing all the files including the hidden files
date	Display a date
cal	Calculator
w	Users using the system
whoami	The current logged in user
whereis	Gives the location of the utility/program in the current directory
rm	Remove
rm -r	Recursively delete
touch	Creates a file
history	Shows the commands applied before on a file/folder
cat	The command ran (kinda like history)
head	The head of the command

 

PERMISSIONS

There are basically three types of permissions in Linux

1.       Read – permission to view content

2.       Write – permission to modify/add

3.       Execute – permission to run a program

These permissions have number values to represent them

·         Read(r) – 4

·         Write(w) – 2

·         Execute(x) – 1

Sample permission string

-rwx -r-x -r-x

This string is divided into three parts

1.       (-) or (-D) for a file or directory

2.       (rwx) for a read, write, and execute permission for the creator

3.       (r-x) for the read and execute permission for the group of users(sort of)

4.       (r-x) for the read + execute permission for everyone logged into the system

 

Change the permission

Command - Chmod 775 filename

·         7 = rwx 4+2+1

·         5 = rx 4+1

·         5 = rx 4+1 filename

We just gave read, write and execute to the creator then read, execute to the group and everyone