Wiki Testing/ServerInstallationGuide6

From OPeNDAP Documentation

1 Testing the Installation

It is possible to test the server to see whether an installation has been properly done. The easiest way to test the installation is with a simple Web client like Netscape. (A command-line web client called getdap is provided with libdap which can retrieve text from Web servers, and print it on standard output. Look for it in the /usr/local/bin directory. If you try it out on a couple of URLs you are familiar with, you'll quickly see how it works.)

You can test the web server installation first, and when you are sure the server is working well, test the OPeNDAP server.

1.1 Testing the Web Server

To begin, confirm that the web server works properly by simply sending a URL for a simple web page, or without a file at all:

http://yourmachine

If you don't get anything with this, examine the document root directory (htdocs), and make a request for a file in that directory:

http://yourmachine/somefile.html

Debugging these early steps is essential to getting an OPeNDAP server to work, but troubleshooting any problems you have with these steps is an issue specific to the web server you are using.

Once you have a web server that can return a web page, you should exercise the CGI configuration. Here is the simplest possible CGI program:

#!/usr/bin/perl
print "Content-type: text/html\n\n";
print "Hello World!\n\n";

Put this text in a file, and try to execute it from the command line. You may have to edit the first line in case your copy of Perl isn't stored in the /usr/bin directory. Don't forget to make the file executable. (Use the chmod command.)

When you can execute this from the command line, put it into the CGI directory (and make sure that the permissions will allow the httpd to execute it), and try to execute it with a URL like this:

http://yourmachine/cgi-bin/test-cgi

If you are configuring your site to use suffixes instead of a directory to identify CGI files, name it accordingly:

http://yourmachine/test.cgi

Entering one of these URLs in a web server should cause the "Hello, World!" text to appear in the web browser window. If not, check the permissions of the CGI program, then consult the documentation for the web server.

If everything works so far, it's time to move on to testing the OPeNDAP server installation.

1.2 Testing the OPeNDAP Server

You can run the handler programs locally, that is, without going over the Internet. Sometimes this is the simplest way to make sure that everything is running.

./dap_nc_handler -o dds  datafile.nc

The program should print the dataset's DDS on standard output. Use the -h option to see the list of options the handlers accept.

The simplest remote test is simply to ask for the version of the server, sending a URL like this:

http://yourmachine/cgi-bin/nph-dods/version

The server will respond to this URL with some text containing release numbers. If you enter this URL into a standard web browser you're doing fine if you see a message like this:

Core version: DODS/3.2.5
Server version: nc/3.2.2

The dispatch script can respond to a number of requests without the assistance of its helper programs, or the existence of any data. Besides the version request, you can also ask for the help and info messages:

> getdap http://test.opendap.org/opendap/nph-dods/data/nc/test.nc.ver
> getdap http://test.opendap.org/opendap/nph-dods/data/nc/test.nc.info
> getdap http://test.opendap.org/opendap//nph-dods/data/nc/test.nc.help

Now we need to test the requests that use the handler programs, such as dap_nc_handler. These programs compose their output by looking at data files, so testing these requires data to be in place.

To return the data attribute structure of a dataset, use a URL such as the following:

> getdap http://test.opendap.org/opendap/nph-dods/data/nc/test.nc.das

The getdap program knows about the DAP protocol, so you can also omit the .das suffix, and use the -a option to the geturl command. This tells getdap to append .das for you:

> getdap -a http://test.opendap.org/opendap/nph-dods/data/nc/test.nc

Refer to The OPeNDAP User Guide for a description of a data attribute structure. You can compare the description against what is returned by the above URL to test the operation of the server.

Check the list of services and helper programs in (Section 1.3). From a web browser, you can access all the DAP services, except the data service, which returns binary, not ASCII, data. That one can only be easily tested from a DAP-enabled client. However, if all the service programs work, and the data service is configured the same way, the odds are on your side.

Using the .html suffix produces the WWW interface, providing a forms-based interface with which a user can query the dataset using a simple web browser. There's more about the interface in The OPeNDAP User Guide .

1.3 Error Logs

When troubleshooting an OPeNDAP data server, the logs of the web server are quite useful. The Apache server keeps two logs, an Access log and an Error log. (You can find these in the logs subdirectory where you installed Apache.) The OPeNDAP server software writes any messages it issues to the error log.

You can make the error messages slightly more verbose by editing the DODS_Dispatch.pm file (in /usr/share/dap-server). Find the $debug variable, and set it to 1 or 2 instead of zero. Note that these messages are, as of version 3.5, now written to the dbg_log file which is usually in /usr/share/dap-server. Check the DODS_Dispatch.pm file to determine the actual path.

1.4 User Support

As a last resort, you can use the OPeNDAP technical support service. OPeNDAP provides technical support by email: support@opendap.org.