Appendix D.1. NetCDF-4 Filter QuickStart

‍For full Filters documentation, see Appendix D. NetCDF-4 Filter Support.

The libnetcdf.so library cannot talk to plugin libraries directly. Instead, it requires an "interface" library, which acts as a go-between. The interface libraries are built by the netCDF libraries, when the underlying plugin libraries are detected during configure/build.

Building and Installing the Interface Libraries

Configuring

When configuring netcdf via either the configure script or via cmake, you'll need to specify the location to install the interface libraries, as follows:

• configure: --enable-plugins --with-plugin-dir=$NCPLUGIN_DIR
• cmake: -DPLUGIN_INSTALL_DIR=$NCPLUGIN_DIR

where $NCPLUGIN_DIR is the path to the user-defined directory, e.g. /usr/local/nc-plugins

After compiling and installing libnetcdf, the interface libraries for those filters detected will be installed in the user-specified NCPLUGIN_DIR.

‍nc-config --plugindir will return the location where plugins were installed.

Using the Interface Libraries at Run-time

For historical reasons, libnetcdf uses the environmental variable HDF5_PLUGIN_PATH to locate the interface libraries at run-time. This location should be set to the $NCPLUGIN_DIR specified when building and installing libnetcdf.

Example Workflow (blosc)

From scratch, the steps to get this to work are as follows, and assumes libhdf5 was installed.

1. Install the filter library, and the associate development headers.
2. Configure netCDF with --enable-plugins and --with-plugin-dir=$HOME/netcdf-plugins
3. Ensure blosc is specified in the generated libnetcdf.settings file.
   
4. Run make, make install.

Once built and installed, set the environmental variable HDF5_PLUGIN_PATH=$HOME/netcdf-plugins.

The reason this works is because:

1. NetCDF builds the interface library.
2. ncdump knows where to find the interface library because HDF5_PLUGIN_PATH is set.