Hyrax - BES Configuration

From OPeNDAP Documentation
Revision as of 15:48, 25 April 2010 by PatrickWest (talk | contribs)

Building the BES and it's data handlers from source, or installing from the Linux RPMs, will provide the default installation with data and a valid configuration. This is suitable for testing. The following details how you go about customizing it for your data.

Location of the BES Configuation File

The BES configuration file is called bes.conf and can be found in $prefix/etc/bes/ if you built the software from source or in /etc/bes/ if you used our RPM packages. By default $prefix is /usr/local.

Basic format of parameters

Parameters set in the BES configuration file have the following format:


If you wish to add to the value of a parameter, then you would use += instead of =


The above would return the values Value1 and Value2 in the software.

And if you would like to include another configuration file you would use the following:


The bes.conf file includes all .conf files in the modules directory with the following:


Note that regular expressions can be used in the Include parameter to match a set of files.

Administration & Logging

The BES.ServerAdministrator parameter is the address used in various mail messages returned to clients. Set this so that whoever gets the email will be able to fix problems ad/or respond to user questions. Also set the log file and log level. If the BES.LogName is set to a relative path it will be treated as relative to the directory where the BES is started. That is, if the BES is installed in /usr/local/bin but you start it in your home directory using the parameter value below, the log file will be bes.log in your home directory.


Because the BES is a server in its own right, you will need to tell it which network port and interface to use. Assuming you are running the BES and OLFS (i.e., all of Hyrax) on one machine, here's what you should do:

User and Group parameters

The BES must be started as root. One of the things that the BES does first is to start up a listener to listen for requests to the BES. This listener is started as root, but then the user and group of the process is set using parameters in the BES configuration file.


You can also set these to a user id and a group id. For example:


Setting the networking parameters

# BES.ServerUnixSocket=/tmp/opendap.socket

The BES.ServerPort tells the BES which TCP/IP port to use when listening for commands. Unless you need to use a different port, use the default. Ports with numbers less than 1024 are special, otherwise you can use any number under 65536. That said, stick with the default unless you know you need to change it.

In the default bes.conf file we have commented the ServerUnixSocket parameter since doing so now disables I/O over that device. If you need UNIX socket I/O, uncomment this line, otherwise leave it commented since the fewer open network I/O ports, the easier it is to make sure the server is secure.

If both ServerPort and ServerUnixSocket are defined, the BES listens on both the TCP port and the Unix Socket. Local clients, on the same machine as the BES, can use the unix socket for a faster connection. Otherwise, clients on other machines will connect to the BES using the BES.ServerPort value. Note that the OLFS always uses only the TCP socket, even if the UNIX socket is present.

Debugging Tip

Use the BES.ProcessManagerMethod parameter to control whether the BES acts like a normal Unix server or not. The default value of multiple causes the BES to accept many connections at once, like a typical server. The value single causes it to accept a single connection, process the commands sent to it and exit, greatly simplifying trouble shooting.


Controlling how compressed files are treated

The bz2, gz, and Z file compression methods are understood by the BES. The BES will automatically recognize compressed files using the 'bz2', 'gzip' and Unix compress ('Z') compression schemes. However, you need to configure the BES to accept those files types as valid data by making sure that the file names are associated with a data handler. For example, if you're serving netCDF files you would set BES.Catalog.catalog.TypeMatch so that it includes nc:.*\.(nc|NC)(\.gz|\.bz2|\.Z)?$; where the first part of the regular expression matches the file name and the '.nc' extension and the second part matches the suffix indicating the file is compressed (either '.gz', '.bz2' or '.Z').

When the BES is asked to serve a file that has been compressed, it first must decompress it and then pass it to the correct data handler (except for those formats which support 'internal' compression such as HDF4). The BES.CacheDir parameter tells the BES where to store the uncompressed file. Note that the default value of /tmp is probably less safe than a directory that's only used by the BES for just this purpose. You might set this to <prefix>/var/bes/cache, for example.

The BES.CachePrefix parameter is used to set a prefix for the cached files so that when a directory like /tmp is used, it's easy for the BES to recognize which files are its responsibility.

The BES.CacheSize parameter sets the size of the cache in megabytes. When the size of the cached files exceeds this value, the cache will be purged using a last-accessed-first-removed approach. Because it's usually impossible to determine the sizes of data files before decompressing them, there may be times when the cache holds more data than this value. Ideally this value should be several times the size of the largest file you plan to serve.

Tuning the cache to your data

The two parameters BES.Uncompress.Retry and BES.Uncompress.NumTries are used, along with BES.CacheSize, to tune the performance of the cache. The BES cache directory is locked to prevent the different beslistener processes from simultaneously removing files and leaving the cache in an inconsistent state. Use the Retry and NumTries parameters to tune this behavior. Generally, NumTries should be set to about 10. The units of Retry are microseconds. To tune the NumTries and Retry, use the formula

Retry = (0.2s/Average_file_sizeMB)/NumTries

If your average file size is 10MB and you've settled on a NumTries of 10, the set Retry to (0.2s/10MB)/10 = 0.002s or 2000 microseconds. If you have really large files (e.g., decompressed they are 500MB), try setting NumTries to 100.


Loading Modules

Virtually all of the BESs functions are contained in modules that are loaded when the server starts up. Each module is a shared-object library. The configuration for each of these modules is contained in its own configuration file and is stored in a directory located in the same directory as the bes.conf file called modules. $prefix/etc/bes/modules/

For example, if you are installing the general purpose server module (the dap-server module) then a dap-server.conf file will be installed in the modules directory. Also, most installations will include the dap module, allowing the BES to server OPeNDAP data. This configuration file is also included in the modules directory and is called dap.conf. For a data handler, say netcdf, there will be an nc.conf file located in the modules directory.

Each module should contain within it a line that will tell the BES to load the module at startup:


Module specific parameters will be included in its own configuration file. For example, any parameters specific to the netcdf data handler would be included in the nc.conf file.

Pointing to data

There are two parameters that can be used to tell the BES where your data are stored. Which one you use depends on whether you are setting up the BES to work as part of Hyrax (and thus with THREDDS catalogs) or as a standalone server. In either case set the value of the .RootDirectory parameter to point to the root directory of your data files (only one may be specified). Use BES.Catalog.catalog.RootDirectory in the dap.conf configuration file in the modules directory if the BES is being used as part of Hyrax, and BES.Data.RootDirectory in bes.conf itself if not. So, if you are setting up Hyrax, set the value of BES.Catalog.catalog.RootDirectory but be sure to set BES.Data.RootDirectory to some value or the BES will not start.

In bes.conf set the following:


And in dap.conf set the following if using Hyrax (usually the case)


By default, the RootDirectory parameters are set to point to the test data supplied with the data handlers.

Next configure the mapping between data source names and data handlers. This is usually taken care of already for you, so you probably won't have to set this parameter. Each data handler module (netcdf, hdf4, hdf5, freeform, etc...) will have this set depending on the extension of the data files for the data.

For example, in nc.conf, for the netcdf data handler module, you'll find the line:


When the BES is asked to perform some commands on a particular data source, it uses regular expressions to figure out which data handler should be used to carry out the commands. The value of the BES.Catalog.catalog.TypeMatch parameter holds the set of regular expressions. The value of this parameter is a list of handlers and expressions in the form handler:expression;. Note that these regular expressions are like those used by grep on Unix and it's somewhat cryptic, but once you see the pattern, it's not that bad. Below, the TypeMatch parameter is being told that any data source with a name that ends in .nc should be handled by the nc (netcdf) handler (see BES.module.nc above), any file with a .hdf, .HDF or .eos suffix should be processed using the HDF4 handler (note that case matters) and that data sources ending in .dat should use the FreeForm handler.

Here's the one for the hdf4 data handler module:


And for the FreeForm handler:


If you fail to configure this correctly, the BES will return error messages stating that the type information has to be provided. However, it won't tell you this when it starts, only when the OLFS (or some other software) actually makes a data request. This is because it's possible to use BES commands in place of these regular expressions, although the Hyrax won't.

Finally, you can configure the types of information that the BES sends back when a client requests catalog information. The Include and Exclude parameters provide this mechanism, also using a list of regular expressions (with each element of the list separated by a semicolon). In the example below, files that begin with a dot are excluded. These parameters are set in the dap.conf configuration file.

The Include expressions are applied to the node first, followed by the Exclude expressions. For collections of nodes, only the Exclude expressions are applied.


If you would like for symbolic links to be followed when retrieving data and for viewing catalog entries, then you need to set the following two parameters. The BES.FollowSymLinks parameter is for non-catalog containers and is used in conjunction with the BES.RootDirectory parameter above. It is NOT a general setting. The BES.Catalog.catalog.FollowSymLinks is for catalog requests and data containers in the catalog and is used in conjunction with the BES.Catalog.catalog.RootDirectory parameter above. The default is set to No in the installed configuration file. To allow for symbolic links to be followed you need to set this to Yes.

The following is set in the bes.conf file:


And this one is set in the dap.conf file in the modules directory:


Parameters for Specific Handlers

Parameters for specific modules can be added to the BES configuration file for that specific module. No module-specific parameters should be added to bes.conf.