11

Week 6 Week 6

The lynx browserApache Web Server

John Wang

With materials courtesy of Inge Mclaurin

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The Catalyst for W3The Catalyst for W3

In 1990, while working for Europe’s high energy physics research lab (CERN), Tim Berners-Lee began to create the basic W3 infrastructure.

CERN’s problem: 1.Results of costly experiments were kept in different

formats on different computers.

2.There was high turn-over rate in CERN. New staff often could not find valuable data left by people who departed. They were “losing” information.

33

The Philosophy Behind W3The Philosophy Behind W3Tim Bernes-Lee proposed “Hypertext” system to organize information.

1. Different files can still be kept on different servers

2. An “index” can link files and information together. This index can direct the end-users to diverse pieces of info on different servers.

3. Users can jump from link to link without any hierarchical restriction.

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W3 InfrastructureW3 Infrastructure

Two main components:

(2) Client browser program (e.g. Lynx, Microsoft Explorer), resides on end-user computers.

(1) Web servers (e.g. Apache server), storing information in Hypertext Markup Language (HTML).

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DaemonDaemon

• “a process that runs in the background and performs a specified operation at predefined times or in response to certain events.”

• The term daemon is a UNIX term

• Microsoft Windows refers to daemons as System Agents and services.

Source: webopedia.com

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DaemonDaemon

A daemon is a program that1. runs continuously 2.exists for the purpose of handling periodic service requests that a computer system expects to receive.

The daemon program forwards the requests to other programs

Source: techtarget.com

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Why do we need to know about Why do we need to know about “Daemons”?“Daemons”?

because...

Each server of pages on the Web has an HTTP Daemon that continually waits for requests to come in from Web clients and their users.

Source: techtarget.com

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The Lynx BrowserThe Lynx Browser• The Lynx browser is a text-based web

browser. http://lynx.isc.org

• Lynx browser is already installed on zenit. – Telnet into zenit.senecac.on.ca– type “lynx” followed by the website you want to

visit, and press ENTER.

$ lynx www.apache.org

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Visiting “apache.org” with lynxVisiting “apache.org” with lynx

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In the beginning… CERNIn the beginning… CERN

• CERN’s original http server was used by all early websites (1991 ~ 1993)

• It was considered to be a big and complex piece of software.

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New Kid on the Block… NCSANew Kid on the Block… NCSA

• Only about 200 websites existed in 1993, when National Center for Supercomputing Applications (University of Illinois) released NCSA Mosaic.

Mosaic was the first readily available graphical web browser.

•NCSA team wanted to create a small web server - so NCSA httpd was born. It quickly became the most popular web server.

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The Apache Web ServerThe Apache Web Server

• Lots of NCSA Mosaic/httpd project team members (mostly students) went to form Netscape company in 1994. NCSA httpd development slowed down, and security holes were not addressed quickly.

• Web administrators around the world shared their changes & modification (patches) of the NCSA httpd.

• They called their effort “A PAtCHy server”, which became “APACHE”

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The Apache Web ServerThe Apache Web Server

• By 1995, there were hundreds of volunteers re-writing and improving the software, making APACHE faster and better.

• Apache has been the most popular web server on the Internet since April of 1996. (Latest Netcraft survey showed that 60% of all websites use Apache. Second place is Microsoft at 30%.)

Source: www.netcraft.com/survey/

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Apache Design PhilosophyApache Design Philosophy

Apache teams wanted to make the software:

1.Open-source: anyone can examine the software code

2.Modular: different add-on (or “mod”) can be developed independently

3.OS independent: Apache is available on many different platforms (Windows, Netware, Unix variances)

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Directories &Directories &Important FilesImportant Files

apachectl

/

home

i120????HOME

binpasswordlogshtdocsconfcgi-bin

httpd.conf.default httpd.conf

index.html

httpd.pid

.htaccess .htpassword

httpd

error_log access_log

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The The confconf directory directory• The conf directory

contains the files used to configure apache.

/

home

i120????HOME

conf

httpd.conf.default

httpd

httpd.conf

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The The httpd.confhttpd.conf file file• The httpd.conf file is

used to configure apache.

• The httpd.conf.default file is a back-up copy of the httpd.conf file.

/

home

i120????HOME

conf

httpd.conf.default

httpd

httpd.conf

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The The binbin directory directory• “bin” is short for “binary”. The

compiled Apache binary files are stored in this directory.

• It contains the file apachectl.

/

home

i120????HOME

httpd

apachectl

bin

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The The apachectlapachectl file file• apachectl is a program

that starts, restarts or stops your Apache daemon/server.

• The file name is “apache” followed by “ctl” which stands for ConTroL

/

home

i120????HOME

httpd

apachectl

bin

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The The htdocshtdocs directory directory• The htdocs directory

contains the files that will be displayed on your webpage.

• For example:– HTML pages– Graphics files– PDF files

/

home

i120????HOME

httpd

htdocs

index.html .htaccess

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The The index.htmlindex.html file file• The index.html file is the

“default” HTML page for a website.

• If the users enters the URL of a site without specifying a HTML page, index.html will be displayed.

/

home

i120????HOME

httpd

index.html .htaccess

htdocs

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The The index.htmlindex.html file file

Example:

http://www.senecac.on.ca

is really.... http://www.senecac.on.ca/index.html

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The The logslogs directory directory• The logs directory contains files

that are logs of events that happen to your server.

/

home

i120????HOME

httpd

logs

httpd.pid

error_log

access_log

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A note on PID numbersA note on PID numbers• A process is the execution of a command by

the UNIX system.

• UNIX assigns a unique process identification (PID) number at the creation of each process.

• As long as a process is in existence, it keeps the same PID number.

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The The httpd.pidhttpd.pid file file• When your server is running it

will contain a file called httpd.pid.

• This file contains the PID of the running server.

/

home

i120????HOME

httpd

logs

httpd.pid

error_log

access_log

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The The error_logerror_log file file• The error_log file contains a

log of all error message generated by your server.

• If you are having difficulty with your server this is the first place you look when trouble-shooting.

/

home

i120????HOME

httpd

logs

httpd.pid

error_log

access_log

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Hint!Hint!

Whenever you have

any

problem

with your

Apache Server...

...the first thing to do is to check your “log

files”

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The The access_logaccess_log file file• The access_log file contains a

log of everyone who logs into your server.

/

home

i120????HOME

httpd

logs

httpd.pid

error_log

access_log

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apachectl

/

home

in120???HOME

binpasswordlogshtdocsconfcgi-bin

httpd.conf.default httpd.conf

index.html

httpd.pid

.htaccess .htpassword

httpd

error_log access_log

password protectionpassword protection

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The The passwordpassword directory directory• In the lab you are asked to

create a password directory.

• This is the directory that will store all the password files.

/

home

i120????HOME

httpd

password

.htpassword

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The The htpassword htpassword filefile• In the lab you are asked to

create a .htpassword file.

• This is the file that will store all the passwords you will create.

/

home

i120????HOME

httpd

password

.htpassword

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The The .htaccess.htaccess file file• You will also create

the .htaccess file in htdocs directory. Its password protects the directory it is stored in.

/

home

i120????HOME

httpd

htdocs

index.html .htaccess

3333

WorkingWorking with with youryour Apache Server Apache Server• Read all the instructions

• Follow all the instructions

• Do one step at a time

• Save Often

• Once completed delete everything and do it all again, and again, and again.

• Keep redoing it until you can do it without help, and without the written instructions.

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Remember...”Ports”?Remember...”Ports”?

• In TCP/IP networking, “port” is not the same as physical/hardware port (e.g. parallel port, serial port)

• "logical connection place" and specifically, using the Internet's protocol, TCP/IP, the way a client program specifies a particular server program on a computer in a network.

Source: techtarget.com

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PortPort

• Port numbers are from 0 to 65536.

• Ports 0 to 1024 (well-known ports) are reserved for use by privileged services. These include telnet, ftp, nntp, etc.

• For the HTTP service, port 80 is defined as a default and it does not have to be specified in the URL.

Example: http://zenit.senecac.on.ca is really http://zenit.senecac.on.ca:80

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http://zenit.senecac.on.ca/~i1201g45/

Your HTML pages on ZenitYour HTML pages on Zenit

• You now access your “public_html” directory through port 80 on Zenit.

/home/i1201g45/public_html/index.html

ZENIT

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http://zenit.senecac.on.ca:7449

Running Apache on zenitRunning Apache on zenit

• By installing Apache in your zenit directory, you need to use an unique port number. Please check my website for your port number.

/home/i1201g45/httpd/ htdocs/index.html

ZENIT