Description of the NERS configuration file

The ners configuration file consists of ascii lines of variable length.
The first line should be 

# NERS Configuration file.  Format version of 2016.12.06

Other lines that start with # are considered comments and are ignored 
by the parser. Keyword lines of configuration are in a form 
KEYWORD: value separated by one or more blanks. If a keyword, except
keyword URL, is defined more than once, the last definition overrides
previous definitions. All keywords should be defined.

Supported keywords:

  URL: value.   Defines the URL where NERS client will download the NERS
                EOP forecast. More than one URL can be defined. 
                If connection to NERS client will not be established 
                during timeout time period, NERS library will try the
                next URL. If it cannot establish connection to the last
                URL fort timeout period, it will stop with error message.

  FCS_FILE:     Name of the local copy of the EOP forecast file. NERS
                writes this file.

  LEAPSEC_FILE: Name of the leap second file. NERS writes this file.

  LTP_USAGE:    Usage of the long tern EOP forecast.

                   stop    -- if the requested epoch is beyond the last
                              epoch of the precise EOP forecast, then
                              stop with the error message.

                   warning -- if the requested epoch is beyond the last
                              epoch of the precise EOP forecast, but still
                              within a range of coarse EOP long-term
                              prediction, to print a warning and compute
                              the EOP using coarse long-term EOP prediction.
                              The warning is printed only once.

                   silent  -- if the requested epoch is beyond the last
                              epoch of the precise EOP forecast, but still
                              within a range of coarse EOP long-term
                              prediction, to compute the EOP using coarse 
                              long-term EOP prediction.

  ON_FAIL_TO_READ: determines behavior of NERS on read failure that may
                   occur mainly due to Internet outage. Supported values:

                   stop    -- issue error message and stop.

                   warning -- issue warning and proceed with the stale
                              version of NERS message. Quality of EOP 
                              prediction may degrade.

                   ignore  -- proceed with the stale version of NERS 
                              message. Quality of EOP prediction may degrade.

  CONN_TIMEOUT: timeout of establishing connection to the NERS server
                and sleep time before attempting to make a new connection.
                Units: sec. Default: 2. Minimum value: 1.

  READ_TIMEOUT: timeout of establishing connection to the NERS server
                and sleep time before attempting to make a new connection.
                Units: sec. Default: 10. NB: NERS forecast length is about
                600 Kb. You may need to adjust this timeout if you have
                very slow or very fast Internet connection. Minimum value: 1.

  LOCK_TIMEOUT: timeout for locking ners files. Since NERS writes and reads
                the message and leap second file, for avoiding reading and
                writing at the same time of more than one process that use
                NERS, Unix locking mechanism is used. To prevent deadlock,
                read and write locks have expiration timeout specified
                by LOCK_TIMEOUT. Recommended value: 8

  N_TRIES:      The number of tries to connect to the server. NERS client
                sleeps for CONN_TIMEOUT between connections. Default: 2.
                Minimum value: 1.

  AGE_FCS:      Maximum age of the local copy of the forecast file. If the 
                age of the local copy of the NERS forecast file exceeds 
                AGE_FCS, NERS client will check the age of the remote
                EOP forecast before computing the internal spline. If the 
                remote NERS forecast is newer then the the forecast in the 
                local copy of the NERS file, NERS library will download the 
                forecast from the remote server and uses the newest version
                for computing internal splines. NERS Will not check the age 
                of NERS client file when it uses internal spline. Unit: sec. 
                Default: 2000. Minimum value: 1000. 

  AGE_SPL:      Maximum age of internal spline. NERS library checks the age 
                of internal spline before computing the EOP at a given epoch.
                If the age exceeds AGE_SPL, the NERS library checks age of 
                the local forecast file. If the age exceeds AGE_FCS, then
                NERS client will check the forecast age at the remote NERS 
                server. If the forecast age at the remote server is newer than
                the forecast age at the local copy, NERS client downloads the
                forecast from the remote server, re-compute the internal 
                spline, and will use the re-compute spline. Default: 2000.
                Minimum value: 1.