# HDF5 Library Environment Variables and Configuration Parameters

## 1. Environment Variables

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:

`HDF5_DEBUG`
  Defines a list of debugging switches documented in the Debugging section of the HDF5 User's Guide.
`HDF5_NOCLEANUP`
  When set to a non-empty value, the programs in the test directory do not remove temporary HDF5 data files. The default is for each test to remove the files before exit.
`HDF5_MPI_OPT_TYPES` (for parallel beta version only)
  When set to `1`, PHDF5 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.
`HDF5_MPI_1_METAWRITE` (for parallel beta version only)
  When set to `1`, PHDF5 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.

## 2. Configuration Parameters

The HDF5 configuration script accepts a list of parameters to control configuration features when creating the Makefiles for the library. The command
`configure --help`
will display the current list of parameters and their effects.

Last modified: 9 September 1998