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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
<html>
  <head>
    <title>HDF5 Library Environment Variables
      and Configuration Parameters</title>
  </head>

  <body>

    <h1>HDF5 Library Environment Variables and Configuration Parameters</h1>

    <h2>1. Environment Variables</h2>

    The HDF5 library uses UNIX environment variables to control
    or adjust certain library features at runtime.  The variables and 
    their defined effects are as follows:

    <center>
      <table width="90%">
	<tr>
	  <th>Variable</th>
	  <th>Description</th>
	</tr>

	<tr valign=top>
	  <td><code>HDF5_DEBUG</code></td>
	  <td>Defines a list of debugging switches documented in the
	    <a href="Debugging.html">Debugging</a> section of the
	    <cite>HDF5 User's Guide</cite>.</td>
	</tr>

	<tr valign=top>
	  <td><code>HDF5_NOCLEANUP</code></td>
	  <td>If set then programs in the test directories do not
	    remove temporary files. The default is for each test to
	    remove the files before exit if the test succeeds but to
	    leave the files if the test fails.</td>
	</tr>

	<tr valign=top>
	  <td><code>HDF5_PREFIX</code></td>
	  <td>The value of this variable is prepended to all temporary 
	    file names created by the test programs and separated from 
	    the base name of the file by a slash. The default is no
	    prefix.</td>
	</tr>

	<tr valign=top>
	  <td><ode>HDF5_DRIVER</code></td>
	  <td>This variable should hold the name of a low-level HDF5
	    file driver such as <code>sec2</code>, <code>stdio</code>, 
	    <code>core</code>, <code>split</code>, or
	    <code>family</code>. The family driver also takes an
	    optional real-valued family member size in MB which
	    defaults to 1. If this variable is not set or empty then
	    the library-defined default file driver is used (which can 
	    be set at configuration time with the H5F_LOW_DFLT cpp
	    constant, usually <code>sec2</code>).</td>
	</tr>

	<tr valign=top>
	  <td><code>HDF5_MPI_OPT_TYPES</code></td>
	  <td>When set to <code>1</code>, parallel HDF5 will use the
	    MPI-optimized code to perform parallel read/write accesses
	    to datasets. Currently, this optimization fails when
	    accessing extendable datasets.  The default is not to use
	    the optimized code.</td>
	</tr>

	<tr valign=top>
	  <td><code>HDF5_MPI_1_METAWRITE</code></td>
	  <td>When set to <code>1</code>, parallel HDF5 will write the
	  metadata via process 0 of each opened parallel HDF5 file.
	  This should improve I/O throughput.  The default is not to
	  use this optimization.</td>
	</tr>

      </table>
    </center>


    <h2>2. Configuration Parameters</h2>

    The HDF5 configuration script accepts a list of parameters to control
    configuration features when creating the Makefiles for the library.  
    The command
    <br>
    <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;configure --help </code>
    <br>
    will display the current list of parameters and their effects.

    <hr>

    <address>
      <a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a>
    </address>

    Last modified: 9 September 1998

  </body>
</html>