UNIX / Linux Getting Started - Unix/Linux

What are UNIX / Linux Getting Started?

What is UNIX?

The UNIX operating system is a set of programs that perform as a link between the computer and the user.

The computer program that allocates the system resources and coordinates all the information of the computer's internal is called the operating system or the kernel.

Users correspond with the kernel through a program known as the shell. The shell is a command line performer; it translates commands entered by the user and converts them into a language that is understand by the kernel.

  • UNIX was originally developed in 1969 by a group of AT&T employees Ken Thompson, Dennis Ritchie, Douglas McElroy, and Joe Hosanna at Bell Labs.
  • There are various UNIX variants available in the market. Solaris UNIX, AIX, HP UNIX and BSD are a few examples. Linux is also a flavour of UNIX which is freely available.
  • Several people can use a UNIX computer at the same time; hence UNIX is called a multiuser system.
  • A user can also run multiple programs at the same time; hence UNIX is a multitasking environment.

UNIX Architecture

Here is a basic block illustration of a UNIX system −

unix_architecture

The most important concept that unites all the versions of UNIX is the following four fundamentals −

  • Kernel − the kernel is the heart of the operating system. It interacts with the hardware and most of the tasks like memory management, task scheduling and file management.
  • Shell − the shell is the utility that processes your requests. When you type in a command at your terminal, the shell interprets the command and calls the program that you want. The shell uses standard syntax for all commands. C Shell, Bourne Shell and Koran Shell are the most famous shells which are available with most of the UNIX variants.
  • Commands and Utilities − There are various commands and utilities which you can make use of in your day to day activities. Cp, my, cat and grip, etc. are few examples of commands and utilities. There are over 250 standard commands plus numerous others provided through 3rd party software. All the commands come along with various options.
  • Files and Directories − All the data of Unix is organized into files. All files are then organized into directories. These directories are further organized into a tree-like structure called the file system.

System Boot up

If you have a computer which has the Unix operating system install in it, then you only want to turn on the system to make it live.

As soon as you rotate on the system, it starts booting up and at last it prompts you to log into the system, which is a movement to log into the system and use it for your day-to-day performance.

Login UNIX

When you first attach to a UNIX system, you generally see a prompt such as the following –

To log in

  • Have your use rid (user identification) and password ready. Contact your system administrator if you don't have these yet.
  • Type your use rid at the login prompt, then press ENTERS. Your use rid is case-sensitive, so be sure you type it exactly as your system administrator has instructed.
  • Type your password at the password prompt, and then press ENTER. Your password is also case-sensitive.
  • If you provide the correct use rid and password, then you will be allowed to enter into the system. Read the information and messages that comes up on the screen, which is as follows.

You will be provide with a command without delay (sometime called the $ prompt) where you kind all your commands. For instance, to check calendar, you need to kind the cal command as follows –

Change Password

All UNIX systems want passwords to help certify that your files and data stay on your own and that the system itself is secure from hackers and crackers. Following are the steps to modify your password −

Step 1 − to begin, type password at the command prompt as exposed below.

Step 2 − Enter your old password, the one you're presently using.

Step 3 − Type in your new password. Always keep your password difficult enough so that nobody can guess it. But make sure, you consider it.

Step 4 − you must validate the password by typing it again.

Note − we have added asterisk (*) here just to explain the location where you need to enter the recent and new passwords otherwise at your scheme. It does not show you any character when you nature.

Listing Directories and Files

All data in UNIX is prepared into files. All files are organized into directories. These directories are organized into a tree-like constitution called the file system.

You can apply the less command to list out all the files or directories accessible in a directory. Following is the instance of using less command with -l selection.

Here entry starting with d..... Stand for directories. For instance, ump, unit and urlspedia are directories and rest of the entry are files.

Who Are You?

While you're logged into the scheme, you might be willing to know: Who am I?

The easiest way to find out "who you are" is to penetrate the whom command –

Try it on your system. This command lists the account name connected with the present login. You can try who am icommand as well to get information about yourself am.

Who is logged in?

Sometime you strength be concerned to know who is logged in to the computer at the same time.

There are three commands obtainable to get you this in order, based on how much you wish to know about the other users: users, who, and w.

Try the w command on your system to check the output. This list down information connected with the users logged in the system.

Logging Out

When you send your session, you need to log out of the system. This is to make sure that nobody else access your files.

To log out

  • Just type the logout command at the command prompt, and the system will clean up everything and break the connection.

System Shutdown

The most regular way to shut down a UNIX system correctly via the command line is to use one of the following commands –

S.No. Command & Description
1
halt
Brings the system down immediately
2
init 0
Powers off the system using predefined scripts to synchronize and clean up the system prior to shutting down
3
init 6
Reboots the system by shutting it down completely and then restarting it
4
poweroff
Shuts down the system by powering off
5
reboot
Reboots the system
6
shutdown
Shuts down the system


You normally need to be the super user or root (the most privileged account on a UNIX system) to shut down the system. Still, on some separate or personally-owned UNIX boxes, a directorial user and sometimes standard users can do so.

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