Introduction To Linux Operating System

Introduction

Linux is a popular version of the UNIX Operating System. It is open source as its source code is freely available. It is free to use. Linux was designed considering UNIX compatibility. Its functionality list is quite similar to that of UNIX.

Components of Linux System

Linux Operating System has primarily three components:

  • Kernel:

    Kernel is the core part of Linux. It is responsible for all major activities of this operating system. It is consists of various modules and it interacts directly with the underlying hardware. Kernel provides the required abstraction to hide low level hardware details to system or application programs.

  • System Library:

    System libraries are special functions or programs using which application programs or system utilities accesses Kernel's features. These libraries implement most of the functionalities of the operating system and do not require kernel module's code access rights.

  • System Utility:

    System Utility programs are responsible for doing specialized, individual level tasks.


Run level in Linux Operating System:

Run level is a state or mode of operating system in Linux. There are "seven" Run levels which is represented by a single digit integer. It is one of the most important Terms in Linux. Linux kernel supports and differentiates all levels.

Seven Run levels are as follows:
  • Run level 0: It means System in haul state, there is no activity.
  • Run level 1: It means system is in "single user" mode. Which are rarely used?
  • Run level 2: It means system is in multiple users’ mode but no network file system (NFS) are there. Which also rarely used.
  • Run level 3: It means system is in multiple users, Command line mode. It is a default run level in most of the Linux system.
  • Run level 4: It means system is in User-definable mode. That is not in used.
  • Run level 5: It means system is in multiple users’ mode with GUI (graphical user interface). This one is the standard run level.
  • Run level 6: It is used when the user wants to restart the system basically for the Reboot sake.
Basic System info Commands for Linux:

Here, I am going to discuss some basic Linux commands through which you can get the information about your system in Linux environment.
  • Cat /proc/memento: It will provide you Memory Information.
  • Cat /proc/CPU Info: It will provide you CPU Information.
  • Date: It will show you current date or time.
  • Whom: It shows who is logged in right now.
  • Do -h: It shows disk usage.
  • Du: It shows directory space usage.
  • Unnamed -a: It shows kernel information.
  • W: It shows who is online.
  • Cal: It shows the current month calendar. 
  • Cat /proc/file systems: It shows the type of current file system which are currently using.
  • Free: It displays available memory in kilo bytes.
  • Cat /proc/version: This command shows what version you are using. And it displays some other information as well.
Keyboard Shortcuts in Linux:

There are different flavours of Linux in the market like Red hat, Centos, Bunt, Debi an etc. Most of the commands are same for all.


UP ARROW: This key will show you previous commands in descending order.
DOWN ARROW: This key will show how your forward command history
CTRL+L: This key will clear your screen.
CTRL+R: This key is used for reverse search, press curler and you can easily access your last run command.
CTRL+P: This key will show you previous history.
CTRL+N: This key will show you forward history.
CTRL+B: This key is use for move cursor one character to the left side.
CTRL+F: This key is use for move cursor one character to the right side.
CTRL+E: This key is use for move cursor to the end of the line.
CTRL+A: This key is use for move cursor to the start of the line.
CTRL+U: This key is use for cut every from the line start to the cursor.
CTRL+K: This key is use for cut every from the cursor to end of the line.
CTRL+W: This key is use for cut the current word before the cursor.
CTRL+Y: This key is use for paste the previous cut text.
CTRL+SHIFT+C: This key is use for copy selected text.
CTRL+SHIFT+V: This key is use for paste you’re last copied by CTRL+SHIFT+C
CTRL+T: It swaps the last two characters before the cursor.
CTRL+M: It behaves like the enter key.
HOME: It will move the cursor at the start of the line.
END: It will move the cursor at the end of the line.
CTRL+D: this key is use for log out the current session.
TAB: This key is most important and special key in Linux, it auto complete the name of the command, file and directory etc.

Linux Boot-up Sequence:

The Linux boot-up sequence basically follows six steps to complete the boot-up sequence. Each step is responsible for (depends on) the next.

Basic Input Output System (BIOS)
  • Searches and executes the boot loader program from the MBR.
  • It is like an abstraction layer between the hardware and the software.
Master Boot Record (MBR):
  • It is located in the first sector of the boot disk. It takes around.
  • Some boot loaders are GRUB, LILO or Linux Loader.
KERNEL: 
  • Located on a disk partition.
  •  It mounts the root file system.
  • It contains drivers for hardware support.
  • It executes the Init program.
INIT PROCESS:
  • Halt
  • Single user mode
  • Multiuser mode without NFS
  • Full multiuser mode
  • Unused, for research
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