File System

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DNS

What is DNS( Domain Name System) ?
=====================================
DNS (Domain Name system) is a wide area where domains and IPs will be resolved.

You can simply resolve a name server to an IP(DNS), also you can resolve an IP to a name server(rDNS).

Name server ( ns1.google.com) 207.45.35.56
| |
| (DNS) | (rDNS)
| |
207.45.35.56 Name server ( ns1.google.com)

As per web hosting industry you can simply assign a name server to an IP at the domain registrar end.

Why DNS?
=====================================
Why we are assigning name servers to IPs? We can't simply keep all the domain's IPs always to view its pages using your computer. Normally humans are not familiar with such high range of numbers.

So we are moving into DNS simply like a telephone directory.

Registering a name server:
====================

To start resolving your domain, you just have to login to your domain registrar end, who is selling domain names(godaddy, namecheap, etc) , and have to register your desired name servers you want to use for your domains.

For example if you are having a domain name as simpledomain.com with godaddy and you want to use ns1.simpledomain.com, ns2.simpledomain.com as name servers for your domains, here you go..

1. First login to your domain seller's login area and register these two name servers with your hosting servers IPs. ( Its better to use two different IPS instead of using single IP).

Ex: ns1.simpledomain.com = 207.45.35.56
ns2.simpledomain.com = 207.45.35.57

2. Then you need to point your domain to those name servers. So the parent name server end settings completed now.

3. Go to the server end now for setting up child name servers. You may need to create two DNS zone records for your name servers and a single DNS zone record for your domain to resolve them properly.

Ex:

;DNS zone record for ns1.simpledomain.com

===============================================
$TTL 86400 ; 24 hours could have been written as 24h or 1d
$ORIGIN example.com.
@  1D  IN  SOA ns1.simpledomain.com. hostmaster.simpledomain.com. (
        2002022401 ; serial
        3H ; refresh
        15 ; retry
        1w ; expire
        3h ; minimum
       )
     IN  NS     ns1.simpledomain.com. ; in the domain
     IN  NS     ns2.simpledomain.com. ; external to domain
     IN  MX  10 mail.simpledomain.com. ; external mail provider
; server host definitions
ns1    IN  A      207.45.35.56  ;name server definition   
www    IN  A      207.45.35.57 ;web server definition
ftp    IN  CNAME  www.simpledomain.com.  ;ftp server definition
; non server domain hosts
bill   IN  A      192.168.0.3
fred   IN  A      192.168.0.4

===============================================

The above zone file would be a simple domain which explains the name server's A records, MX records and all. To know what is A record, MX records and CNAME, you can refer the following links;

http://kb.siteground.com/article/DNS_Records_NS_A_MX_CNAME_SPF_Explained.html
http://www.itsyourip.com/dns/dns-records-explained/

So you have now configured DNS zone record for your name server. After allowing 24-48 hours your name server will start to ping from your server with the assigned IP on your DNS zone record.

At the same time if you point your domain to these registered name servers your domain will start to resolve from your server.

=====================================
How DNS works with here?

Once registering name servers and pointing your domain to those registered name servers, what will happen?

1.Once you hit a domain name on your browser, it will produce a DNS query will be accessing all the global DNS cache and will get its name servers which is assigned to it on that domain's registrar end.
2. Once the DNS query got the name servers, it will look for the IPs assigned to it on the name server's registration end, and will find the appropriate IP.
3.Once after getting the IP details, the DNS query will look for the appropriate server which has that specific IP address.
This is bit network related, every router on DNS would have a router table which will be having the IP address info, so while the DNS query passed them over, it will find the corresponding server which has the IP assigned with it and will reach the server.
4. After reaching the server the DNS query will interact with the bind service and will look for the corresponding domain's zone records to see if its existing. If so, the A records will be addressed and hence the domain is resolved.

If its the same server IP, the web server virtual host entry would be checked then appropriate web directory will be displayed on your browser as the domain main page.

Continue...........

Working principle of E-mails

KEY TERMS

MTA - Mail Transfer Agent (post office)
MDA - Mail Delivery Agent (post box)
MUA - Mail User Agent (post man or people who retrieving the mails from postbox)








(Schema)







To keep everyone from checking other users' emails, MDA is protected by a user name called a login and by a password.

When an organisation's email server is improperly configured and allows third-party users on any network to send emails, this is called an open relay.


CONCEPT

Email is based around the use of electronic mailboxes. When an email is sent, the message is routed from server to server, all the way to the recipient's email server. More precisely, the message is sent to the mail server tasked with transporting emails (called the MTA, for Mail Transport Agent) to the recipient's MTA. On the Internet, MTAs communicate with one another using the protocol SMTP, and so are logically called SMTP servers (or sometimes outgoing mail servers).

The recipient's MTA then delivers the email to the incoming mail server (called the MDA, for Mail Delivery Agent), which stores the email as it waits for the user to accept it.

Some comman MTA's in Unix based Operating system

• exim
• sendmail
• postfix
• qmail
• courier mail server
• zimbra
  

Some comman MDA's in Unix base Operating system

• binmail, the MDA part of Sendmail
• fdm - A combined mail retrieval agent and mail delivery agent
• maildrop
• postdrop
• postfix-maildrop - A mail delivery agent for use with the postfix mail transport agent
• procmail
• courier-maildrop
• dovecot - A mail server suite that includes a mail delivery agent

Some comman MUA's

Graphical:

• Kmail
• Courier
• Mozilla Thunderbird
• Opera Mail
  

Text-Based:

• Alphine
• Mutt
  

Web-Based:

• Horde IMP
• RoundCube Webmail
• SquirrelMail
• Zimbra

Nostradamus

The Seven Most Startling Ancient World Mysteries, and How Unlocking Their Secrets May Contain the Answers to Mankind's Biggest Questions

This world holds many mysteries, and at World Mysteries.com, we strive to keep you up on new strange happenings, new insights into older discoveries, and new developments into unraveling what we cannot understand yet.

And, we're out to show you how an understanding of such mysteries can help you find answers to some of the questions you have.

In this, the first one of our articles on ancient world mysteries and how they relate to you, we'll focus on Nostradamus.

Nostradamus, the Future, and You

A Claim to Clairvoyance

Nostradamus was a doctor during the time of the Black Plague in the 16^th century in France. After the Plague killed his beloved wife and two children, he lost his livelihood and wandered the country for six years. He recovered and returned to help the sick and dying. In his 50's, he remarried and started writing his quatrains, prophetic verses, separated in seven sections, which he called Centuries.

His book gained instant acclaim, and he even was summoned to court by the French Queen, Catherine de Medici. Nostradamus died at 63 years of age, but he's leaving a great and sometimes troubling set of visions and prophecies as his heritage.

Forecasts for the Future

Nostradamus did not only forecast what would happen during his lifetime and in the immediate future after his death, but also things that have happened in our not too distant past, and things that will happen in our future. To protect himself, he shrouded his quatrains in obscurity, but at other times, he is chillingly literal and even mentions names. Here are some of the things he forecast many years before they happened:

1. Hitler - Even though Nostradamus calls him "Hister," It's clear he's talking about Hitler in this quatrain:

• Beasts ferocious with hunger will cross the rivers,
  The greater part of the battlefield will be against Hister.
  Into a cage of iron will the great one be drawn,
  When the child of Germany observes nothing.

2. Napoleon - Many prophecies of Nostradamus concern France, and the name "Napoleon," changed like a word game but still recognizable, shows up in many of his quatrains. This quatrain clearly describes Napoleon:

• An Emperor will be born near Italy
  Who will cost the Empire dearly.
  It will be said when his allies are seen
  That he is less a Prince than a butcher.

1. The Atomic Bomb - There are many references to terrible wars and great destruction, and here is one, loosely translated, that tells of the atom bomb and the destruction it brings:

§ Near the gates and within the cities
there will be two scourges the like of which was never seen,
famine within plague, people put out by steel,
crying to the great immortal God for relief.

Troublesome Times Ahead

Nostradamus also gave prophecies for our times, forecasts that will affect your life. Even though they aren't always clear, you can get information about the future and the future of the United States. Here are just some of the potential things you can be looking for in the future, as prophesied by Nostradamus:

· Great Advancements, Peace and Prosperity - In this very straightforward quatrain, Nostradamus describes our modern world with the amazing scientific and technical advancements we now enjoy:

o Pestilences extinguished, the world becomes smaller,
For a long time the lands will be inhabited in peace:
People will travel safely through the sky (over) land and wave:
Then wars will start anew.

· Obama Elected to be the New President - This quatrain refers to a person of low ancestry who would gain a very high office in the union. And, that person will put an end to a very unpopular war:

o There will be peace, union and change,
Estates, offices, low high and high very low:
To prepare a trip, the first offspring torment,
War to cease, civil process, debates.

· World War III - Nostradamus often referred to great misery, plagues and wars, and many believe that this quatrain describes the beginning of WW III, with rockets coming from the sky:

o During the appearance of
The bearded star, the three
great princes will be made
enemies. The shaky peace on
earth will be struck by fire
from the skies. Po, The
winding Tiber, a serpent placed
on the shore.

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Swine Flu

Swine Flu Death Toll : 214

A Virus Emerges

Novel influenza A (H1N1) is a new flu virus of swine origin that first caused illness in Mexico and the United States in March and April, 2009. It spreads mainly through the coughs and sneezes of people who are sick with the virus, it may also be spread by touching infected objects and then touching your nose or mouth. Symptoms including fever, cough, sore throat, body aches, headache, chills and fatigue. In addition, many people also have reported nausea, vomiting and/or diarrhea.

How to be safe:

1. Cover your mouth and nose while coughing and sneezing.
2. Try not to touch your eyes, nose and mouth frequently.
3. Washing and sanitizing your hands frequently is a very effective way.
4. There is no restriction on food and drinks as Swine flu is not a food borne illness.
5. Drink loads of water and get enough sleep. Try to avoid close contact with sick people.
6. Stay away (3-feet distance) from people who have a respiratory infection.
7. Ventilate and allow the entry of sun in the house and all enclosed places.