Linux Introduction

What is Linux?

Linux is, in simplest terms, an operating system. It is the software on a computer that enables applications and the computer operator to access the devices on the computer to perform desired functions.

The operating system (OS) relays instructions from an application to, for instance, the computer’s processor.

The processor performs the instructed task, then sends the results back to the application via the operating system.

What is Kernel mean?

In computing, the kernel is the central component of OS.

It is a bridge between applications and the actual data processing done at the hardware level.

The kernel’s responsibilities include managing the system’s resources (the communication between hardware and software components).

What is CPU ?

It runs the Operating System and applications, constantly reviving input from the user or active software programs.

It processes the data and produces output, which may stored by an application or displayed on the screen.

Here are some CPU types:

• INTEL (x86)
• SPARC  (SUN / Oralce)
• POWER  (IBM)
• AMD

How CPU speed measured?

Clock Speed

• The most common measure of CPU speed is the clock speed, which is measured in MHz or GHz. One GHz equals 1,000 MHz, so a speed of 2.4 GHz could also be expressed as 2,400 MHz. The higher the clock speed, the more operations the CPU can execute per second.
• It’s important to realize that the clock speed of a CPU is not the only factor determining performance. Because of differences in chip architecture, one processor may be able to perform more operations than another over one cycle. Therefore, even if the first processor has a lower clock speed than the second, it may actually be faster.

Multi-Core Technology

• Some processors are “dual core” or “quad core.” These terms indicate the use of multiple CPUs on a single circuit. The idea behind this concept is to improve processing speed by using two or more processors that can run independently or coop

Lets talk about Memory

Computer memory is any physical device capable of storing information temporarily or permanently. For example, Random Access Memory (RAM) is a volatile memory that stores information on an integrated circuit  used by the Operating System, application and hardware.

Front Side Bus and Cache

• With any processor, the cache and front side bus play an important role in speed. The CPU and front side bus work together, so they should ideally run at the same speed so that one cannot slow the other down.
• The cache also plays an important role in processor speed. The cache is memory that is accessed by the CPU to aid in completing certain routine tasks faster, so the larger the cache, the greater the CPU performance.

Volatile vs. non-volatile memory

Memory can be either volatile and non-volatile memory.

Volatile memory is memory that loses its contents when the computer or hardware device loses power.

Computer RAM is an example of a volatile memory and is why if your computer freezes or reboots when working on a program, you lose anything that hasn’t been saved.

Non-volatile memory, sometimes abbreviated as NVRAM, is memory that keeps its contents even if the power is lost. EPROM is an example of a non-volatile memory.

Remember Memory is not a Storage Disk

It is very common for new computer users to be confused by what parts in the computer are memory. Although both the hard drive and RAM are memory, it is more appropriate to refer to RAM as “memory”   and a hard drive as storage.

When a program such as your Internet browser is open, it is loaded from your hard drive and placed into RAM, which allows that program to communicate with the processor at higher speeds. Anything you save to your computer, such as a picture or video, is sent to your hard drive for storage.

UNIX Principles

• Everything in UNIX is a file (including hardware)
• Small, single purpose programs
• Ability to chain programs together to perform complex tasks
• Configuration data stored in text

Logging in to LINUX system

• Two types of login screens available
• Virtual consoles (Text based) & Graphical logins (display managers)
• RHEL use GNOME/KDE display manager
• Run-level-3 is a text based & Run-level-5 is Graphical based.
• Up-to 6 virtual consoles & one graphical console
• Switch among the virtual consoles ( Ctrl-Alt-F[1-6])
• Access the graphical console by typing Ctrl-Alt-F7

Super User here is ROOT user

• Special administrative account
• Also called super user
• Root has complete control over system
• SU creates new shell as root
• SUDO commands runs command as root
• <id> command shows who you are?

Important Directories you must know

1. Home Directory           –    /root , /home/<username>
2. User Executable         –    /bin, /usr/bin,/usr/local/bin
3. System Executable     –    /sbin, /usr/sbin, /usr/local/sbin
4. Other mounts              –    /media , /mnt
5. Configuration              –    /etc
6. Temporary files           –    /tmp
7. Kernels & boot loader  –  /boot
8. Server Data                 –  /var , /srv
9. System information     –  /proc, /sys
10. Shared libraries           –  /lib,/usr/lib, /usr/local/lib

Learn about RUN Levels in LINUX

• A run-level is a system state that is defined by the services listed in /etc/rc.d.
• Configuration file to update run-level
• $ vi /etc/inittab à update line “ id:3:initdefault:
• To check which run level your are now $ who -r
• You can change the run level just by typing # init0 or init6 # init 5

LEVEL	NAME	DESCRIPTION
0	Halt	Immediately shuts down system and powers it off, if it can
1	Single user	Brings system to a bare essentials mode for maintenance
2	User-defined	Custom
3	Multi-user with console only	All services are running but X11
4	User-defined	Custom
5	Multi-user with display and console	All services are running including X11 (or GUI)
6	Reboot	Reboots the machine

What is Open source Linux?

• Software & Source code available to all
• Freedom to distribute software and source code
• Ability to modify and create derived works
• Integrity of author’s code

FEDORA Project  (Open Source)

• community support
• Personal systems

RHEL (Red Hat Enterprise Linux)

• Stable, thoroughly tested software
• Professional support servers
• Centralized Management tools for large networks