Features of Linux OS

LINUX:

• Linux Kernel or Linux is an operating system kernel used by a family of Unix-like operating systems.  
• Linux distribution is used to refer to various operating systems built on top of Linux Kernel.
• The Linux kernel is released under the GNU General Public License version 2 (GPLv2) and developed by contributors worldwide.
• Linux is one of the most prominent examples of Free / Open Source software.

How Linux Load while switch on the system:

System on
|
BIOS(Boot Strap)
|
Boot Loader(Grub)
|
O/S Operates

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I/O & Other peripherals

Difference Between Closed and Open Source Softwares:

Linux Operating System Parts :

1. Kernal
2. Shell
3. File Structure
4. Utilities

1. Kernel:

• Kernel is Central component of computer operating systems (OS). 
• Its responsibilities include managing system's resources (communication between hardware and software components). 
• Kernel -->Monolithic in Linux--> Core part of OS. It controls all part such as H/W and  S/W.

Monolithic:

• Heavily loaded to control all operations
• Complex and difficult to maintain.

Micro Kernel:

• Micro Kernel has only basic functionalities
• Additional components will handle remaining tools.
• Easy to maintain

2. Shell:

• A shell is a Command Interpreter and it provides an interface for user. It receives ommand from user, then interprets and sends commands to kernal for execution.

3. File Structure:

• In Linux file structure files are grouped according to purpose. 
• For ex: commands, data files, documentation. 
• This file structure organizes way of files are stored in a storage device such as   disks and printers. 
• All directories are grouped under root entry " / ". 

The Directories under Root are listed below:

root  -- The home directory for the root user
home -- Contains the user's home directories along with directories for services

1. FTP
2. HTTP
3. Samba
4. George

bin -- Commands needed during bootup that might be needed by normal users. Almost all user commands are in /bin or /usr/local/bin.
sbin -- Like bin but commands are not intended for normal users. Commands run by LINUX.
proc -- This filesystem is not on a disk. It is a virtual filesystem that exists in the kernels imagination which is memory. A directory with info about process number . Each process has a directory below proc.
usr -- Contains all commands, libraries, man pages, games and static files for normal operation.
include -- Header files for the C programming language. Should be below /user/lib for consistency.
lib -- Shared libraries needed by the programs on the root filesystem. Unchanging data files for programs and subsystems.
X11R6 -- The X windows system files. There is a directory similar to usr below this directory.
X386 -- Like X11R6 but for X11 release 5
boot -- Files used by the bootstrap loader, LILO. Kernel images are often kept here.
modules -- Loadable kernel modules, especially those needed to boot the system after disasters.
man -- Manual pages
info -- Info documents
doc -- Documentation  
dev -- Device files
etc -- Configuration files specific to the machine.
skel -- When a home directory is created it is initialized with files from this directory
sysconfig -- Files that configure the linux system for devices.
var -- Contains files that change for mail, news, printers log files, man pages, temp files
file
local -- The place for locally installed software and other files or Variable data for programs installed in /usr/local.
lock -- Lock files. Used by a program to indicate it is using a particular device or file
log -- Log files from programs such as login and syslog which logs all logins and logouts.
run -- Files that contain information about the system that is valid until the system is next booted
spool -- Directories for mail, printer spools, news and other spooled work.
tmp -- Temporary files. Programs running after bootup should use /var/tmp.
catman -- A cache for man pages that are formatted on demand
mnt -- Mount points for temporary mounts by the system administrator.

4. Utilities:

• These are specialized programs such as editors, compilers, and communication programs that performs standard computing operations.