As your Cactus executable runs, standard output and standard error are usually written to the screen. Standard output provides you with information about the run, and standard error reports warnings and errors from the flesh and thorns.
As the program runs, the normal output provides the following information:
A report is made as each of the thorns in the ActiveThorns parameters from the parameter file (see Section B3.2) is attempted to be activated. This report shows whether the thorn activation was successful, and if successful, gives the thorn’s implementation. For example
If any of the parameters in the parameter file does not belong to any of the active thorns, or if the parameter value is not in the allowed range (see Section C1.4.1), an error is registered. For example, if the parameter is not recognised,
or if the parameter value is not in the allowed range,
The scheduled routines (see Section C1.5) are listed, in the order that they will be executed. For example,
Usually a thorn registers a short piece of text as a banner. The banner of each thorn is displayed in the standard output when the thorn is initialised.
Output methods in Cactus are all provided by thorns. Any number of output methods can be used for each run. The behaviour of the output thorns in the standard arrangements are described in those thorns’ documentation.
In general, output thorns decide what to output by parsing a string parameter containing the names of those grid variables, or groups of variables, for which output is required. The names should be fully qualified with the implementation and group or variable names.
There is usually a parameter for each method to denote how often, in evolution iterations, this output should be performed. There is also usually a parameter to define the directory in which the output should be placed, defaulting to the directory from which the executable is run.
See Chapter C2.7 for details on creating your own I/O method.