UNIX OPERATING SYSTEM

Multitasking Multi-user










          
 
 
 
 
 
 
 
 

Kernel Layer: The inter most layer of the operating system software. It is the only layer that interacts directly with the hardware.

Service Layer: Accepts service requests from the command layer and translate them in to detailed instructions to the kernel

Command Layer (or the Shell): The outermost layer. Provides the user interface. It is the only part of the operating system which users can interact directly.
 
 

The Service Layer consists of set of programs that provide the following type of services :
 


The Unix Operating System was born in 1969. It was invented by Ken Thompson and Dennis Ritchie at Bell Labs. Unix was originally written in assembly Language. Programs written in Assembly are machine - dependent. To make Unix portable Thompson and Ritchie rewrote Unix in C (1973). They create C Language to make Unix portable.

There are two major variation of Unix Operating System:
 


And many different flavors:
 


Unix Features:

  1.     Portability (machine independent)
  2.     Multi-user
  3.     Multitasking
  4.     Hierarchical File System
  5.     Device - independent Input and Output operations
Unix Utilities:

Unix include more then one hundred utility programs, also called commands, these utilities include following:
 

Unix Shells:            Bourne Shell (created by Stephen Bourne)
                              Korn Shell    ---->  for Industry
                              C Shell         ---->  compatible with C language
 


Log in
                         Unix Network Protocol ---->  TCP/IP
 
 

         %  <---  C  Shell prompt (most common)
        $   <---  Corn or Bourne prompt (most common)
 
 

Example:
 

            Initial log - Netware Prompt
            ---> Enter your login name                  (Unix is case sensitive - Netware is not)
 

            Second login prompt is for Linux or SCO
            --->  Unix prompt  -->  login name:  (case sensitive!)

            For Linux  --->   ~$ ---> bash (Bourne Again Shell) prompt
 


 
 

Linux Operating System    (Most common and stable: Red - Hat, Caldera, Slackware)
 

Linux is a version of Unix that was developed by Linus Torvald for PC's with 386, 486, or Pentium Processors. Linux is available free under a public license.
 

Linux Shells :         Bourne Again Shell (created by Stephen Bourne)
                              Public Domain Korn Shell
                              TC Shell
 
 
 

        ~$ ---> bash (Bourne Again Shell) prompt


 

The Unix boot up process
 


 
 
 
 
 

Getty -  establishes communication between the Unix server and the Dumb Terminal
 

Validation Information is created by the administrator  ---->   superuser :  /etc/passwd
 

 
~$PS1                 ~PS1="Bog\w\$"    ---->  working directory
 
p --> prompt                                          Bog~$           --->   user home directory
S --> string                                            Bog~$pwd    --->    print working directory
1 --> one                                                          (displays the absolute path to the current directory)
 


 
 
~$cd^..  --> (..) parent of the current directory

/home$

/home$cd^..

/$cd(enter)

~$

 ~$cal         --->   calendar

~$mesg^n  --->  stop the messages
 

With superuser permission you can log to other computer :

~$cd^/home/unix(x)/