Internal and External Commands in Linux UNIX

Internal Command

Internal commands are the commands that are executed directly by the shell. These commands will not have a separate process. You can’t find these commands in PATH directories in system because these are built in shell command. echo is an external command and if you try to find its path it will show shell built in.

$ type echo

echo is a shell builtin

when you run echo the system will not search in PATH location, it will execute it from shell builtin commands that are stored in some separate file.

Pipes and Redirection

Pipes and Redirection are one the powerful features of Linux Operating System. These are used for sending data stream from input to output or you can say from source to destination.

File Descriptor and Redirection

File descriptor is of three types.

Standard Input (fd 0), Standard Output (fd 1) and Standard Error (fd2)

GNU-Linux

What is GNU and its relation with Linux

GNU/Linux is open source in nature. Because the source code for programs is publicly available, anyone can take part in development, fixing a small bug or by developing and distributing a complete major application.

Home Directory in Linux

Home Directory

In Linux every users have their own directory in which they work, it is called the home directory of that user. You can set permissions so that other users can not access this directory or they can read but cannot write or whatever you want.

The directory in which you find yourself when you first login is your home directory.
Its path is generally

Linux Booting Process

Introduction: 

Linux is Open source Operating System. We can check starting, stopping of operating system, where it loads specified programs using their particular configurations and permits you to change those configurations to control the boot process, and shuts down in a graceful and organized way. 

Beyond the question of controlling the boot or shutdown process, the open nature of Linux makes it much easier to determine the exact source of most problems associated with starting up or shutting down your system. A basic understanding of this process is quite beneficial to everybody who uses a Linux system.

Absolute Path Vs Relative Path In Linux

Absolute Path Vs Relative Path In Linux:

Absolute Path: An absolute path is defined as specifying the location of a file or directory from the root directory(/). In other words we can say absolute path is a complete path from start of actual filesystem from / directory.

example:
/home/user/Document/srv.txt
/root/data/dev.jpg
/var/log/messages

All are absolute Path.

Linux : ls command

ls Command:

ls is the most basic command of Linux. It list information about the FILEs (the current directory by default). 

ls command examples:

1- Listing files:

$ ls

2- List directory with relative path

$ ls /home/user

Basic Linux Command

Basic Linux Command : Here are some basic command of Linux with example. Everyone working on Linux should have knowledge of these commands.

Linux Filesystem Hierarchy

Linux Filesystem or Directory Structure

Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents, the names, locations, and permissions for many file types and directories in Linux.

The Directory Structure of Linux is as Below.

Linux Architecture

The Linux operating system is composed of four major subsystems: Hardware, Kernel, Shell and user interface.

There are two important parts one is Kernel and other is Shell. The Kernel interacts with the machine's hardware and the Shell interacts with the user.


1. User Applications
The set of applications in use on a particular Linux system will be different depending on what the computer system is used for, but typical examples include a word-processing application and a web-browser. The user program or application that needs to access the hardware use the services of Kernel. These programs access the kernel through a set of function called System Calls.

Linux Features

Following are some of the important features of Linux Operating System.


Portable - Portability means software can works on different types of hardware in same way. Linux kernel and application program supports their installation on any kind of hardware platform.

Open Source - Linux source code is freely available and it is community based development project. Multiple teams’ works in collaboration to enhance the capability of Linux operating system and it is continuously evolving.

What is Linux

Linux

Linux is, in simplest terms, an operating system, assembled under the model of free and open source software development and distribution.  

Operating System

Operating systems are computer programs. An operating system is the first piece of software that the computer executes when you turn the machine on. The operating system loads itself into memory and begins managing the resources available on the computer. It then provides those resources to other applications that the user wants to execute.