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NETWORK OPERATING SYSTEMS
By: Waqas Ahmed
(C.E.O at Treesol)
BUILD THE CONCEPTS
Understanding Linux components and structure
Linux System Architecture
Linux System Architecture is consists of following layers:
1.
2.
3.
4.
Hardware Layer
Kernel
Shell
Utilities
Linux System Architecture
Hardware
Hardware consists of all peripheral devices like:
RAM
Hard Disk
CPU
etc…
Kernel
Kernel is the core of Linux Operating System, while the system is operational, it keeps
on running.
The kernel is the part of the Linux Operating system which consist of routines, which
interact with underlying hardware, and routines which include system call handling,
process management, scheduling, the file system, and high-level part of the I/O
system.
You can say, it is a low level program interfacing with the hardware.
The kernel is the first part of the operating system to load into memory
during booting (i.e., system startup), and it remains there for the entire duration of
the computer session because its services are required continuously.
The best known kernel is Mach kernel.
Shell
Shell is an interface between a user and a Linux operating system, i.e. user interacts
with the Linux operating system through the shell.
There may be two tasks to be performed by a shell. First, accepts commands from a
user and second, interprets those commands.
Without a shell it would be hard to make your system actually do something.
The shell is just a program - there are several different shells for Linux, each of them
offering different features.
Most Linux systems use the Bourne Again Shell (Bash) and C Shell (CSH). One other
shell, which is rather complex, is Korn shell (KSH).
Linux shells support multitasking (running several programs at once).
Utilities
Utility programs giving user most of the functionalities of an operating systems.
Like: Spreadsheets, word processors, paint, etc…
Shell and Kernel Works Together
Shell accepts commands from use interpret them and deliver these interpreted
commands to kernel for execution.
After execution, the shell displays result of executed commands.
Whenever you try to start a process with the shell, the shell has to ask the kernel to
make it.
Main Components of Linux System
The Linux system has 3 main components:
1. Kernel
2. System Libraries
3. System Utilities
Kernel
We already discussed in prvs slides.
System Libraries
"System Libraries" describe a typical set of functions through which applications can
interrelate through the kernel.
Or you can say “System Libraries” are special functions or programs using which
application programs or system utilities accesses Kernel's features. These libraries
implements most of the functionalities of the operating system and do not requires
kernel module's code access rights.
Because a kernel can't do much out of itself, it must be triggered to perform tasks.
Such triggers are made by applications, but these applications must of course know
how to place system calls for the kernel. So system libraries help them to access and
trigger.
The most well-known system library for Linux systems is the GNU C Library, also
known as glibc.
System Utilities
These are the programs that execute individual, particular and specialized managing
tasks.
Some of the system utilities may be invoked just once to initialize and configure some
features of the system; others may run enduringly,
What is Partition ?
A partition is a section of a hard disk.
When you format a hard disk, you can
usually choose the number of
partitions you want.
The computer will recognize each
partition as a separate disk.
File System
The term filesystem has two somewhat different meanings, both of which are
commonly used. This can be confusing to novices, but after a while the meaning is
usually clear from the context.
One meaning is the entire hierarchy of directories (also referred to as the directory
tree) that is used to organize files on a computer system. On Linux and Unix, the
directories start with the root directory (designated by a forward slash), which
contains a series of subdirectories, each of which, in turn, contains further
subdirectories, etc.
The DOS, Windows, OS/2, Macintosh, and UNIX-based operating systems all have file
systems in which files are placed somewhere in a hierarchical (tree) structure.
File systems specify conventions for naming files. These conventions include the
maximum number of characters in a name, which characters can be used, and, in
some systems, how long the file name suffix can be. A file system also includes a
format for specifying the path to a file through the structure of directories.
File System
The second meaning is the type of filesystem, that is, how the storage of data (i.e.,
files, folders, etc.) is organized on a computer disk (hard disk, floppy disk, CDROM,
etc.) or on a partition on a hard disk.
Each type of filesystem has its own set of rules for controlling the allocation of disk
space to files and for associating data about each file (referred to as meta data) with
that file, such as its filename, the directory in which it is located, its permissions and
its creation date.
Linux File System Types
There are many file systems used in Linux, some are:
minix, ext, ext2, ext3, xia, msdos, umsdos, vfat, proc, nfs, iso9660, hpfs, sysv, smb,
ncpfs
Different File System Comparison
What is Boat Loader ?
Most simply, a boot loader loads the operating system.
When your machine loads its operating system, the BIOS reads the first 512 bytes of
your bootable media (which is known as the master boot record, or MBR).
The master boot record itself holds two things:
1. Either some of or all of the boot loader program
2. The partition table (which holds information regarding how the rest of the media
is split up into partitions).
When the BIOS loads, it looks for data stored in the first sector of the hard drive, the
MBR; using the data stored in the MBR, the BIOS activates the boot loader.
Human-Computer Interface
A way for humans to interact with computers.
There are two modes in which we can work on Linux.
1. GUI (Graphical User Mode)
2. CLI (Command Line Interface)
Graphical User interface (GUI)
A graphical user interface (GUI) uses windows, icons and menus and which can be
manipulated by a mouse.
Using a GUI is fairly easy because it provides the users with a few basic operations
that can be learned quickly.
GUIs allow users to take full advantage of the powerful multitasking capabilities of
modern operating systems by allowing such multiple programs and/or instances of a
program to be displayed simultaneously.
Command Line Interface (CLI)
A command line interface (CLI) relies solely on textual input and output and use only
text and are accessed solely by a keyboard.
The CLI gets its name from the fact that it is an interface which contains command
lines.
A command line is a space on the display screen in which commands are typed in by
the user. Pressing the ENTER key after typing in a command causes that command to
be passed to the shell.
A console is the display mode for which the entire monitor screen is occupied by a
CLI. CLIs are also provided by terminal windows, which are text-only windows that
can be opened in a GUI and which emulate a console.
The most familiar example of a CLI to many people is MS-DOS.
GUI vs CLI
RED HAT ENTERPRISE LINUX GUI OVERVIEW
Live Practically
Done in Class.