XMM-Newton Science Analysis System: Users' Guide

2.7 General settings affecting all SAS tasks

The behaviour of a task is modified by the following environment variables:

• SAS_PATH is a list of colon-separated directories that contain SAS packages. It should at minimum contain the toplevel directory where the SAS is installed.

• SAS_CCF points to the directory containing the Current Calibration File (CCF) or contains the name of the Calibration Index File. If a value is provided via the command line option -i (see above) this takes precedence over any environment specification. This variable is only relevant to tasks making use of the Calibration Access Layer.

• SAS_CCFFILES has the same meaning as the command line option -f. If a list of CCF constituents is given both via -f and SAS_CCFFILES the former takes precedence over the latter. This variable is only relevant to tasks making use of the Calibration Access Layer.

• SAS_ODF points to a directory containing an ODF or to a SAS summary file (*SUM.SAS). If a name is specified via -o and SAS_ODF is defined the former takes precedence over the latter. This environment variable is only relevant to tasks making use of the ODF Access Layer.

• SAS_TRACER determines the debug level of the libraries.

• SAS_MEMORY_MODEL determines how the internal memory is used by the data access (through the Data Access Layer, DAL). There are basically two options for the memory model: High Memory (high) and HighLow Memory (highlow or low) model. In the high model every time a dataset is opened it is kept entirely in memory and all subsequent operations are performed on the memory-loaded dataset. In the low model the data is loaded into memory only when their access is needed (when opening a dataset only their attributes are kept in memory). While the high model should bring higher performance, its use implies normally a high memory consumption, which can lead to swapping, producing a poorer performance. Therefore for machines with less than about 1GB RAM it is recommended to use the low model. The default value for SAS_MEMORY_MODEL is high

• SAS_VERBOSITY determines the debug level of the task. The value ranges from 0 to 10 with increasing verbosity level. The default value is 1, a value of 4 is recommended for getting a very communicative SAS, larger values should be only used for debugging purposes.

SAS tasks produce error messages at levels called message, warning, error and fatal.

• At message level, a message is reported to the user and processing continues.
• At warning level, a warning message is reported to the user and processing continues.
• At error level, an error message is reported and current operation is aborted. Control may return to the calling program which can take an appropriate action.
• At fatal level, a fatal error is reported to the user and all processing is aborted. A fatal error is generated if the internal state of the program is disrupted, for example if an invalid value is found in a variable.

Error messages are characterised by a layer and a verbosity level. The layer indicates the layer in the system where the message is coming from (e.g. application, user interface, application library or system library). The verbosity level determines whether or not the message will be reported. The user can specify the verbosity level. If the verbosity of a message is large enough compared to the system verbosity level, the message will be reported. The verbosity level differs for the different layers.