UserGuideAppendix

From OPeNDAP Documentation
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Installing the OPeNDAP Software

The current version of the Distributed Oceanographic Data System core software is \OPDversion . Note that this number applies only to the core software. The individual servers, clients, and client libraries have their own version numbers.

Full information about the latest versions of the OPeNDAP software is available from the OPeNDAP web site: \OPDhome .

This version of OPeNDAP uses CGI standard 1.1.1.

Acquiring the OPeNDAP Software

The OPeNDAP Web Site

We recommend that you use the \OPDhome to obtain the most current version of the software. The "Software" page includes a form for selecting OPeNDAP components. Completing the form automatically creates a custom compressed archive of all the software components you selected, which you can then download to your own machine.

Whenever possible, you should use the provided binary software rather than t rying to compile and link OPeNDAP yourself. Compiling will work, but the OPeNDAP software is large, and it takes a long time to compile.

Don't forget to select the core software as well as the specific data access API or server you need. For an OPeNDAP client, you will also need Tcl/Tk and gzip.


By Anonymous FTP

The OPeNDAP software may be down-loaded by anonymous ftp from the \OPDftp .

Don't forget to down-load the core software tar file as well as the tar file corresponding to whatever data access API you need.

The OPeNDAP project provides a small number of archive files containing linked libraries and executables for some computing platforms. You should use these files whenever possible, to avoid the hassle of compiling the software yourself. The OPeNDAP software is a substantial chunk of code, and it takes a long time to compile and link.

Installing the Software

To install the OPeNDAP software, choose a directory to be the OPeNDAP root directory. This directory must be identified with the DODS_ROOT environment variable for the OPeNDAP software to run.

First, set the working directory to the DODS_ROOT directory.For example, 

export DODS_ROOT=/usr/local/DODS
cd $DODS_ROOT


Next, expand the archives with gzip and unpack the expanded files with tar: 

gzip -d DODS-88772.tar.gz
tar -xvf DODS-88772.tar

If you got the files via anonymous ftp, you would have to repeat the process for each down-loaded archive file, specifying the name of each component file. For example: 

gzip -d DODS-core-2.19.tar.gz
tar -xvf DODS-core-2.19.tar

Building the OPeNDAP Core

Unpacking the core software archive will create a configure script in the DODS_ROOT directory. The core software may then be built with: 

cd $DODS_ROOT
./configure
make

If you downloaded binary files, you can skip the "building" steps.

Building an OPeNDAP Client or Server

Unpacking the client library archives in the DODS_ROOT directory will produce directories such as jg-dods for the JGOFS software and nc-dods for the netCDF software. These will appear in the src subdirectory under DODS_ROOT. Each of these directories will also be equipped with a configure script to create a makefile, so the build procedure for them is the same as for the core software, for example: 

cd $DODS_ROOT/src/nc-dods
./configure
make


Getting the Software Used by DODS

Several pieces of software are required to run OPeNDAP. These are all free software, and are descibed in \appref{req-software}.

Installing the OPeNDAP Libraries

In order to link and run client programs, the only OPeNDAP software that must be installed are the OPeNDAP libraries. The following libraries, described in ( opd-client,link) must be installed in the /usr/lib directory, or somewhere else where the linker will find them. Simply copy them into that directory from the OPeNDAP distribution.


  • libdap++.a
  • The OPeNDAP version of the API your software uses.

In addition to the OPeNDAP libraries, the following software is also required to link an OPeNDAP client. You can obtain them from the \OPDhome or \OPDftp . (Look under your machine type, then under DODS/packages/lib.) The first two libraries should be part of the Tcl/Tk distribution. The other three libraries are GNU software.

  • libtcl.a
  • libexpect.a
  • libstdc++.a
  • librx.a (Regular expression software. Part of the

regex package.)

  • libz.a (Compression software. Part of the gzip

distribution.)

To run an OPeNDAP client, you should have the wish and gzip programs in the PATH, and the following Tcl programs must be either in the DODS_ROOT/etc directory:


  • dod_gui.tcl
  • progress.tcl
  • error.tcl

An OPeNDAP client will still execute without these programs, but important functionality, including the GUI manager and the data compression will be absent. Refer to the INSTALL file included in each distribution for specific information about setting up the client.


The OPeNDAP Client Initialization File (.dodsrc)

The following section refers only to OPeNDAP clients from release 3.2 and after.


When an OPeNDAP client starts up, it checks to see whether the user has an initialization file available to control the setting of a number of parameters having to do with caching, proxy servers, and other http issues. If this file is not found, one is created in the user's home directory, using default values.\footnote{The default values enable a maximum cache size of 20

megabytes, a cache expiration time of 24 hours, and no proxy servers.}

The client initialization file is usually called .dodsrc, and is usually located in the user's home directory. You can change this by creating an environment variable called DODS_CACHE_INIT and setting it to the full pathname of the configuration file. As of OPeNDAP version 3.4, you should use DODS_CONF instead. DODS_CACHE_INIT is deprecated, and will disappear in future releases.

Here is a sample configuration file:

\begin{vcode}{inb}

  1. Sample configuration file

USE_CACHE=1 MAX_CACHE_SIZE=20 MAX_CACHED_OBJ=5 IGNORE_EXPIRES=0 CACHE_ROOT=/home/user/.dods_cache/ DEFAULT_EXPIRES=86400 PROXY_SERVER=http,http://dcz.dods.org/ PROXY_FOR=http://dax.dods.org/.*,http://dods.org/ NO_PROXY_FOR=http://dcz.dods.org DEFLATE=1 ALWAYS_VALIDATE=0

Comments

Starting a line with a \# makes that line a comment.

Caching

The parameters on lines 2 through 7 control caching. The OPeNDAP client can store data you've requested on your local computer. If you repeat a request, the data can be retrieved from this local cache, saving the expense of a network connection. Most web browsers operate the same way. You can control the caching behavior with the following configuration file parameters.

CACHE_ROOT
This parameter contains the pathname to the

cache's top directory. If two or more users want to share a cache, then they must both have read and write permissions to the cache root.

MAX_CACHE_SIZE
The value of MAX_CACHE_SIZE sets the maximum size of the cache in megabytes. Once the cache reaches

this size, caching more objects will cause cache garbage collection. OPeNDAP will first purge the cache of any stale entries and then remove remaining entries starting with those that have the lowest hit count. Garbage collection stops when 90\ purged.

MAX_CACHED_OBJ
This parameter sets the maximum size of

any individual object in the cache in megabytes. Objects received from a server larger than this value will not be cached even if there's room for them without purging other objects.


Many web documents, and OPeNDAP data, are delivered with an expiration date in their header information. Generally, this is done for time-sensitive information that may not be valid after the expiration date. You can control the behavior of the OPeNDAP client with respect to expiration dates with two configuration file parameters.

IGNORE_EXPIRES
If the value of this parameter is 1

(one), then expiration dates will be ignored, and the caching behavior will be ruled by the DEFAULT_EXPIRES parameter.

DEFAULT_EXPIRES
Any data received without an expiration

time will expire in the number of seconds given by this parameter. If IGNORE_EXPIRES is zero, this will apply to all data, whether or not it comes with an expiration date. The value is given in seconds. The configuration in the example is set for 24 hours.

Proxy Servers

An OPeNDAP client can negotiate proxy servers, with help from directions derived from its configuration file. There are three parameters that control proxy behavior. There can be more than one of each of these declarations.

PROXY_SERVER
This identifies a proxy server to use for

all OPeNDAP requests, except for requests specifically modified by the other two proxy behavior directives. The format is: 

PROXY_SERVER=\var{protocol},\var{proxy_URL}

Where \var{protocol} is the name of an internet protocol, and \var{proxy_URL} must be a full URL to the host running the proxy server. HTTP is the only internet protocol supported by DODS, so \var{protocol} will always read http. There can be more than one proxy declaration, in which case, the OPeNDAP client will use the first proxy server on the list that responds.

PROXY_FOR
The PROXY_FOR parameter provides a way to specify that URLs which match a regular expression should be

accessed using a particular proxy server. The syntax for PROXY_FOR is: 

PROXY_FOR=\var{regular expression},\var{proxy_URL}[,\var{flags}]

Where \var{regular expression} is an expression which matches the URL or group of URLs. For example `http://dax.dods.org/.*\.hdf' would match a URL ending in `.hdf' at dax.dods.org. The regular expression uses the POSIX basic syntax.\var{proxy_URL} is the same as above.

The \var{flags} parameter is an optional integer that configures the regular expression matcher. A value of zero sets the default. The four flag values and their meanings are:


REG_EXTENDED
If set, use the POSIX extended syntax

regular expressions. To set this, add 1 to the value of \var{flags}.

REG_NEWLINE] If set, then . and [\^{ ...
}

don't match newline. Also, the regular expression matcher will try a match beginning after every newline. Set this by adding 2 to \var{flags}.

REG_ICASE
If set, then we consider upper- and

lowercase versions of letters to be equivalent when matching. Set by adding 4 to \var{flags}.

REG_NOSUB
If set, then when PREG is passed to regexec, that routine will report only success or failure, and nothing about the

registers. Add 8 to \var{flags} to set this.

You can find a brief tutorial to regular expressions in the OPeNDAP bookshelf\texorhtml{. See the OPeNDAP documentation page at \OPDhome}{at \OPDregex}.

NO_PROXY
Use this parameter to say that access to a

certain host should never go through a proxy without using the more complicated regular expression syntax. The syntax of NO_PROXY is: 

NO_PROXY=\var{protocol},\var{hostname}


Where \var{protocol} is as for PROXY_SERVER, \var{hostname} is the name of the host, not a url.

Compression

Many OPeNDAP servers support compression of the returned data. This can save network bandwidth, and transmission time. You can tell your client to ask the server for compressed data by including a line in your .dodsrc file like this: 

DEFLATE=1

Using a value of zero will make the client request only uncompressed data. If the directive is omitted, the default value is zero.

Validation

Caching data locally can be risky if the data in question change often. The ALWAYS_VALIDATE option controls whether the OPeNDAP client checks the validity of the cached data. The validity check in this case is simply a comparison of the date the data was cached with the "Last-modified" date of the remote data. If the configuration value is set to 1, the client will always validate the cached data. If set to 0, the data will not be validated (but may expire, according to the cache policy set by the DEFAULT_EXPIRES configuration directive).

If the directive is omitted, the default value is zero. That is, the default behavior is not to validate the data.

Software you will need for OPeNDAP

To do anything with DODS, you'll need to be able to unpack the archive files you can download from the OPeNDAP site. To save space and transmission time, the archive files are compressed with the gzip program. You will have to have a copy of that program to unpack the OPeNDAP software.

Most of the software you need for OPeNDAP is avaliable from the GNU archives. Refer to \xlink{http://www.gnu.org}{http://www.gnu.org} forinstructions. Look at \xlink{http://www.gnu.org/order/ftp.html}{http://www.gnu.org/order/ftp.html}for a list of mirrors of that archive. Use the mirror closest to you, the transmission will be faster.

gzip
This is the GNU compression and de-compression program.

You will need to install it before you can unpack any of the other

software described here. This package is not

available in the OPeNDAP distribution, since it is used to unpack the

distribution archive files.

Follow the instructions to install each of the following software packages. Typically, you would install a package called foo as follows: 

gzip -dc foo.tar.gz | tar xvf -
cd foo
./configure
make
make install

This is simply a guide, of course, and the installation instructions for each software package should be followed carefully.


Running an OPeNDAP Server

If you use one of the platforms for which OPeNDAP supplies a binary distribution, you only need the following software to run an OPeNDAP server.

Perl
Perl is used for the server dispatch script. (See

( opd-server,arch).) This is the main CGI program

constituting the OPeNDAP server. You must have Perl version 5 or

later. (Alternatively, you can also rewrite the dispatch script to

use another scripting language, such as your shell. However, we

think installing Perl is generally a simpler task.) You can get

Perl from the GNU archives, or from

\xlink{http://www.perl.com}{http://www.perl.com}.

Running an OPeNDAP Client

If you use one of the pre-compiled, out-of-the-box, OPeNDAP clients, you will need no additional software to run OPeNDAP. However, you can use the "GUI" feature of the OPeNDAP client\footnote{This is not to be confused with the OPeNDAP Matlab or IDL GUIs, which are clients of their own. This is simply a client feature that can display transmission and error information to the user.} by installing the following software. We recommend this, as it provides useful information about the progress of data transmission or error conditions.

Tcl/Tk
The Tcl language and Tk libraries are available from

\xlink{http://www.scriptics.com}{http://www.scriptics.com}. You should install the entire package, including the wish interpreter program\footnote{You can also use a safe Tcl interpreter. Refer to the Tcl documentation for information.} and the expect package. The wish interpreter is part of the Tcl/Tk core distribution package. This package is also available in the OPeNDAP distribution, but the one available from the Tcl site may be more current.

Building OPeNDAP

If you need to build the OPeNDAP software, or link it to existing libraries, you will need the following GNU software. Refer to \xlink{http://www.gnu.org}{http://www.gnu.org} forinstructions. Look at \xlink{http://www.gnu.org/order/ftp.html}{http://www.gnu.org/order/ftp.html}for a list of mirrors of that archive. Use the mirror closest to you, the transmission will be faster.

GNU \Cpp Compiler
OPeNDAP needs g++, the GNU \Cpp compiler

to compile.

binutils
The GNU linker is part of this package.
libstdc++
The standard \Cpp library.
GNU Make
GNU Make is not essential, but will make like easier.
flex
The GNU lexical-analyzer generator
bison
The GNU parser generator.
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