1. INTRODUCTION
This paper will provide a guide for those in the National
Weather Service (NWS) who wish to establish
a World Wide Web (WEB) server on the Scientific Applications Computer
(SAC). The paper outlines how to
connect the SAC to the Internet, how to obtain free WEB server
software and how to install it. The SAC is the
cornerstone of the SOO/SAC Program, a NWS program providing the
Science and Operations Officer (SOO) at each
NWS Weather Forecast Office with tools for on-station research,
training, and professional development
(Bruehl 1996). Since some technical information is presented, a basic
knowledge of computer skills,
especially in the UNIX environment, is assumed. It is also assumed
that the reader has a general knowledge of
the Internet and the World Wide Web. However, some references and
resources are provided to supply
additional information.
The WEB encompasses a vast amount of real time, research,
reference and general meteorological
information, as well as enormous amounts of information on nearly any
other subject. The World Wide Web
offers tremendous potential for research and professional
development. In addition, operating a WEB server
provides a relatively easy way to share and display large amounts of
meteorological and other types of data.
2. GETTING CONNECTED
There are numerous ways to connect to the Internet. Probably the
most logical way is through a
direct connection. This involves having a dedicated, high capacity
line that connects your computer to the
Internet. If you have direct access to the Internet through an
educational institution or commercial service,
the process is quite simple. All that it is involved is plugging in
the hardware, connecting the line and
configuring your system.
Connecting your SAC directly to the Internet provides the
potential to have your own WEB server.
The WEB server is a program that enables you to distribute WEB pages
directly off your computer. Without a
direct Internet connection and an associated WEB server, you will
need to have your WEB pages distributed by
another machine. Most NWS users will have their SAC already connected
to the Internet, but if you do not,
Peggy Bruehl, the NWS SOO/SAC coordinator, who maintains the SOO/SAC
Home Page has some instructions
available at:
http://www.comet.ucar.edu/pub_html/sac_html/index.html(see Bruehl
1995).
3. SETTING UP A WEB SERVER
Installation of a WEB server allows the maximum potential for
the development of applications
associated with WEB documents, including the use of optional features
such as Common Gateway Interfaces (CGI)
to support interactive documents and other application programs. To
run your own WEB server you will need to
have direct Internet access on the machine in which you intend to run
the server. Servers can run on most
types of computer platforms. NCSA, the National Center for
Supercomputing Applications, has compiled and
uncompiled versions of their WEB server, HTTPd, available as
freeware. The following pages contain
information on the installation, compilation, configuration, startup,
shutdown, and testing of the NCSA WEB
server.
The instructions and guidelines are based on information from the
NCSA HTTPd Home Page (see NCSA 1995a),
The WEB Server Book (see Magid et al. 1995) and Managing Internet
Information Services (see Liu et al. 1994).
The current version of NCSA's Web server is HTTPd_1.5.2. The SAC
is a Hewlett Packard model HP 715/64
that operates on the HP-UX 9.03 UNIX operating system and NCSA has an
uncompiled version of HTTPd available
for this machine.
a. Compilation of NCSA HTTPd Server Software
[Note : In the following, lines that are bold and begin with % are
to be inputted by the user.]
The NCSA HTTPd source code is available from the following
WEB address and by anonymous ftp, respectively:
http://hoohoo.ncsa.uiuc.edu/docs/setup/compilation.html
ftp://ftp.ncsa.uiuc.edu/Web/httpd/UNIX/ncsa_httpd/current/
httpd_source.tar.Z
To begin the compilation process, login as root. Before
getting the source code, you need to create the /usr/local/src
directory.
% mkdir /usr/local/src
Change to the /usr/local/src directory.
% cd /usr/local/src
Get the source code via the WEB or FTP and save it as
ncsa_source.tar.Z in the /usr/local/src directory.
The following command will unpack the code.
% zcat ncsa_source.tar.Z | tar xvf -
The unpacking process will create a subdirectory
called httpd_1.5.2 that contains a README file, the
Makefile, and several subdirectories. Subdirectories
include cgi-bin, conf, icons, logs, src, and support.
To build the HTTPd server binary, change directories
to the source directory and make a backup copy of the
Makefile using the following commands:
% cd httpd_1.5.2/src
% cp Makefile Makefile.dist
Now edit the original Makefile while keeping in
mind not to change any variables unless you know exactly
what they do. The Makefile can be edited in any text
editor; for the SAC you can use the text editor associated
with the edit button on the VUE panel.
Define which compiler is used on your machine by
uncommenting the Makefile line referring to your
particular compiler. The SAC has a cc compiler. Select
the cc compiler by removing the # in front of the cc
line while ensuring that a # is in front of the other
lines that refer to different compilers.
You are now ready to compile the server. Type in
the following command:
% make hp-cc
This will compile the source code. After compilation
is over, the HTTPd binary needs to be copied into its
permanent directory.
Copy the HTTPd binary into the /usr/local/etc/httpd
directory.
% cp /usr/local/etc/httpd/src/httpd /usr/local/etc/httpd/
b. HTTPd Configuration
There are three configuration files located in
the /usr/local/etc/httpd/conf directory which must
be modified.
The three configuration files are:
httpd.conf The main server configuration file
srm.conf The server resource configuration file
access.conf The global access control file
These files are originally found with a .conf-dist
file extension. Make copies of these with a new
extension of .conf, using the .conf-dist as originals
for safe keeping and reference.
% cp httpd.conf-dist httpd.conf
% cp srm.conf-dist srm.conf
% cp access.conf-dist access.conf
1) Standard httpd.conf setup file
The httpd.conf controls most of the basic and
technical elements of server operation. For general public
access to the server the httpd.conf file should be configured
with the following settings. Under most circumstances the
default value for the settings will be fine, but there are a
few settings which need to be adjusted. A brief summary of the
more important settings are listed below.
ServerType: The default setting of standalone
should be used under most circumstances.
ServerRoot: This setting is the direct path to
the directory where you put the httpd binary.
It also determines where the files that will be served are
located. The default is /usr/local/etc/httpd/
ServerName: The official hostname of your server
as it appears in the URL.
ServerAdmin: The E-mail address given to users to report
problems or comments. This provides a consistent address
for your site even if the administrator changes. It is usually
of the form Webmaster@your.domain.
User and Group: This defines the user id (UID) and the group
id (GID) that the server uses. These settings are often a
problem for those first beginning WEB administration. It may
take a little adjusting to do this correctly. The default
UID is nobody and the GID is -1. If there is a problem,
trial and error will work best here.
Port: The network port on which the server
is running. The default is 80.
StartServer: The number of servers launched into
the pool of operating servers when HTTPd is started. The default
value is fine under most circumstances.
MaxServer: The maximum number of servers available
in the server pool. The default value is fine under most
circumstances.
PidFile: The name of the file where the
original server logs its own process id number. The default
setting is fine and this will send the data to /logs/httpd.pid.
ErrorLog: The default path to /logs/error_log is fine.
Agentlog: The default path to /logs/agent_log is fine.
RefererLog: The default path to /logs/referer_log is fine.
Look over the setup one more time and then save it.
2) Standard srm.conf setup file
The srm.conf file controls how the HTTPd serves
files. Under most circumstances the default values for
the settings will be acceptable. The following is a
general description of two of the more common settings.
DocumentRoot: This setting specifies the directory
from which the files, images or other documents are
served from. The default setting is
/usr/local/etc/httpd/htdocs. The htdocs directory may
need to be created if it was not done so during the
unpacking process earlier. This can be done with the
following command:
% mkdir /usr/local/etc/httpd/htdocs
Files or documents outside of this directory
can still be served with the use of a symbolic link.
A symbolic link is a Pointer to another directory or
file. To set up a symbolic link use the following
command:
% ln -s /the path to where you want files served from/
/usr/local/etc/httpd/htdocs/
UserDir: This setting specifies which directory users
on the system can use to serve files to the public from
their home directories. The default value is public_html
which allows users on the system to serve files in
Their own public_html directories. To prohibit this
possible security risk, set UserDir to DISABLED.
The remaining settings or directories in the
srm.conf configuration file will only need to be
Adjusted if you implement advanced or technical features
on your WEB server.
3) Standard access.conf setup file
The access.conf controls certain security issues,
access to certain directories, and the type of access
WEB browsers have to your WEB server. For general,
public access to the server you should configure the
access.conf file with the following settings.
Under most occasions the default value for the settings
should do, but here is a general description of the
more common settings.
AllowOveride: Change this setting from All to None,
This enables another layer of security.
Options: Change the options setting from
Indexes to FollowSymLinks. This directive prohibits
users from randomly looking through your directory.
Directory: This is the second directory directive.
It should be changed to whatever directory you have set
the document root to.
c. HTTPd Server Startup
The server is easily started from the command
Line by executing the binary with the following command:
% /usr/local/etc/httpd/httpd &
The server will need to be started every time
the SAC is rebooted. To get the server to start on its
own every time the machine is booted up, you will need
to edit the inittab file. Add the following line to
the inittab file which is usually located in the
etc directory.
home::bootwait:/usr/local/etc/http/httpd &
d. HTTPd Server Testing
To test the server and see that it is running, type in
the following:
% telnet localhost 80
Where the 80 above is the network port server your
server is operating on. You will see the following:
trying...localhost aaa.aaa.aaa
Escape character is ctrl]
Where aaa.aaa.aaa is the host domain name of your
address. This opens up a connection to your server. To
test the server, type in the following and hit
return rapidly twice.
% HEAD/HTTP/1.0
You will see the following status message:
HTTP 1.5 OK
e. HTTPd Server Termination
To kill the server identify the process id
number and then kill it.
% ps -ef
% kill [process id number]
Or change directories and kill the log file.
% cd /usr/local/etc/httpd
% kill 'cat /logs/http.pid'
f. WEB Server Security
Security is an extremely important issue on the Internet. If you
are not directly connected to the
Internet and only access it through dial-in capability then there is
little threat from the outside. However,
if your system is directly connected to the Internet then there is a
security risk. The first thing to keep
in mind is that it is very important to have a good security setup on
the host system. Once you are confident
of this, then you need to look at the setup of the server itself.
When configuring your server there are several things you can do
to improve the security. The two
biggest directives to change for security reasons are in the
access.conf setup file. Change the AllowOveride
directive to None and change the Options directive to FollowSymLinks
(NCSA 1995b).
For more advanced security concerns there are many more options.
Security at the advanced level can
be quite a complex subject and to ensure the brevity of this
document, a full discussion is not included.
However, two popular methods for serious security concerns are worth
mentioning. The first method, firewalls,
are a special type of gateway host which acts as a wall between your
network and the Internet. The firewall
is setup to prohibit most traffic from going into your system and
allowing data to go out. More information
on firewalls and firewall tool kits are available on-line at
http://www.zeuros.co.uk/firewall. Another
popular method is the use of wrapper programs, particularly the
program TCP Wrappers. These programs act as a
wrapper around the server program. The software allows you to setup
the program to accept or deny any
connection based on various criteria while maintaining a log of all
attempted network connections. More
information on TCP Wrappers is available at
ftp://ftp.win.tue.nl/pub/security.
4. CREATING A WEB PAGE
The HyperText Markup Language (HTML) is composed of a set of
elements that simply enhance and
determine the display of a simple text document. There are numerous
versions of HTML, each new version is
usually just an expanded version of an older one. Different browsers
and different versions of a particular
browser can read different versions of HTML. Nearly all browsers can
read the earliest versions of HTML.
Numerous descriptions of the most commonly used HTML elements as well
as new elements and features are
available on-line. Three recommended on-line resources include HTML
Quick Reference (see Grobe 1995), HTML
Elements List (see Hannah 1995) and A Beginner's Guide to HTML (see
NCSA 1996). The Appendix lists some of
the most commom HTML elements.
Remember that the World Wide Web (WEB) is a network of computers
that supply WEB documents, data,
multimedia information and much more. The Home Page is the first
place or first document you see when you
visit a particular WEB site. The Home Page usually provides a
greeting, an introduction, and an index of all
the information available at that particular site. It is important to
keep in mind that HTML is an evolving
language, and different WEB browsers may recognize slightly different
sets of HTML elements.
5. SUMMARY
This training and applications note contains the basic
information needed to establish a presence on
the World Wide Web for those members of the NWS community who have
access to a SAC. Instructions and
references have been presented discussing how to connect the SAC to
the Internet, obtain free WEB server
software, install the server software, and use the basic techniques
of WEB page creation. The WEB offers a
relatively reliable, cost effective, and easy means to share and
receive large quantities of meteorological
information. The WEB contains a vast amount of material on nearly any
other subject as well. Operating a WEB
server allows you to pursue opportunities in community outreach,
public relations, research, and professional
development. The possibilities are unlimited.
REFERENCES
Bruehl, P., National Weather Service-Office of Meteorology, cited
1995: Connecting your SAC to the Internet. [Available on-line from
http://www.comet.ucar.edu/pub_html/sac_html/ README/internet.html.]
_____, P., National Weather Service-Office of Meteorology, cited
1996: SOO/SAC Home Page. [Available on-line from
http://www.comet.ucar.edu/pub_html/sac_html/index.html.]
Grobe, M., Academic Computing Services, The University of Kansas,
cited 1995: HTML Quick Reference. [Available on-line from
http://kuhttp.cc.ukans.edu/lynx_help/HTML_quick.html.]
Hannah, M J, Sandia National Laboratories, cited 1995: HTML Elements
List [Available on-line from
http://www.sandia.gov/sci_compute/elements.html.]
Liu, C., J. Peek, R. Jones, B. Buus, and A. Nye, 1994: Managing
Internet Information Services. O'Reilly & Associates, INC., 630 pp.
Magid, J., R. D. Mathews, and P. Jones, 1995: The Web Server Book.
Ventana Press, 315 pp.
NCSA, cited 1995a: The NCSA HTTPd Home Page. [Available on-line from
http://hoohoo.ncsa.uiuc.edu/.]
_____, cited 1995b: Making Your Setup More Secure. [Available on-line
from http://hoohoo.ncsa.uiuc.edu/docs/tutorials/security.html.]
_____, cited 1996: A Beginner's Guide to HTML. [Available on-line
from http://www.ncsa.uiuc.edu/General/Internet/WWW/HTMLPrimer.html.]
APPENDIX
1. INTRODUCTION TO HTML DOCUMENTS
The following section shows the basic elements needed to create an
HTML document. A sample HTML document and
its results are included.
a. Elements placed in the body
Text Elements
<p>...</p>
This element marks the beginning and end of a paragraph that
will be formatted before it is displayed
on the screen. This allows a paragraph to keep its continuity on the
screen by eliminating line breaks.
<pre> . . . </pre>
Identifies text that has already been preformatted in some
format and must be displayed with these
characteristics. Such text may include prearranged columns or tables.
<blockquote> . . .
</blockquote>
Includes a section of text quoted from some other source.
Hyperlinks or Anchors
A hyperlink is an element that links the current WEB document to
other WEB documents. An anchor must
include a name or href attribute, and may include both. There are
several optional attributes, but they are
rarely encountered.
<a href="URL"> . . . </a>
Link to another file or WEB resource.
<a name="anchor_name"> . . .
</a>
Define a target location in a WEB document.
<a href="#anchor_name"> . . .
</a>
Link to a target location in the same WEB document.
Headers
<h1> . . . </h1> Largest Font
<h2> . . . </h2>
<h3> . . . </h3>
<h4> . . . </h4>
<h5> . . . </h5>
<h6> . . . </h6> Smallest Font
Physical Styles
<b> . . . </b>
Boldface
<I> . . . </I>
Italics
<u> . . . </u>
Underline
<ul>. . . </ul>
Present an unordered list
<ul>
<li>An item in the list
</ul>
<ol>. . . </ol>
Present an ordered list
<ol>
<li>An item in the list
</ol>
b. An Example HTML Document
The following set of code is a portion of the HTML document that
contains information for the Skywarn
Spotter Organization at the NWSFO Albany, NY. This portion of the
code contains many different HTML elements
such as images, font changes, ordered lists, line breaks, as well as
hyperlinks to meteorological images and
text from other WEB servers. Figure A1 represents a screen snapshot
of the browser's interpretation of the code.
<html>
<head>
<title>
NWSFO Albany Skywarn
Homepage</title>
<body alink="#FF0000"
vlink="#3232CD" link="#0000FF"
bgcolor="#FFFFFF" text="#000000"
<body>
<center>
<h4>
<A
HREF=http://nwsfo.atmos.albany.edu/>| NWSFO Albany Home
Page | </a>
</center>
</h4>
<img src="top2.gif">
<H2>
<IMG SRC="skywarn2.gif"
align=middle> NWSFO Albany Skywarn
<br>
<br>
A Source of Information for Emergency Managers & Storm Spotters
</H2>
<IMG
Src="line.marble1.gif">
<h4>
<ul>
<IMG
Src="abball.gif"><a
href=skywrncls2.html>Skywarn
Fall/Winter Training Classes Announced
!</a>(10/05/96)
<br>
<IMG
Src="abball.gif"><a
href="#whatsky">What is
Skywarn?</a>
<br>
<IMG
Src="abball.gif"><a
href="#join">How To Join
Skywarn?</a>
<br>
<IMG
Src="abball.gif"><a
href="#skynews">Skywarn News
</a>(10/06/96)<br>
<IMG
Src="abball.gif"><a
href="#Current">
Current Weather Data</a>
<br>
(Current weather data...watches...warnings and information)
<br>
<IMG
Src="abball.gif"><a
href="#fcst">
Current Forecasts & Forecast
Data</a>
<br>
Current forecasts...discussions and information)
<br>
<IMG Src="abball.gif">
StormBuster OnLine(A Newsletter for Emergency Managers & Storm
Spotters)
<br>
</body>
</html>
Figure A1. Screen snapshot of the Netscape browser interpretation of
code.
Figure A1
NWSFO Albany Skywarn Homepage
A Source of Information for Emergency Managers & Storm Spotters
Current Weather Data
(Current weather data...watches...warnings and information)
Current Forecasts & Forecast Data
Current forecasts...discussions and information)
StormBuster OnLine(A Newsletter for Emergency Managers & Storm Spotters)
Figure A1. Screen snapshot of the Netscape browser interpretation of code.
Figure A1