# Executioner System

The Executioner block describes how the simulation will be executed. It includes commands to control the solver behavior and time stepping. Time stepping is controlled by a combination of commands in the Executioner block, and the TimeStepper block nested within the Executioner block.

The PETSc package is used as the underlying solver in MOOSE, and provides a wide variety of options to control its behavior. These can be specified in the Executioner block. Please see the online PETSc documentation for detailed information about these options.