To help you maintain your overall work environment, JES2 provides an interactive means to control much of its function and the devices under its control. Although the JES2 environment is initially determined through initialization statements, you can alter many of those definitions as the system's workload changes or your installation adds new devices or needs to redefine its overall configuration. JES2 provides commands to request current status of devices and functions and JES2 responds with informational messages. Based on those messages, the operator, system programmer or automated operations program, such as NetView® for z/OS® or System Automation for z/OS (SA z/OS), can issue further commands to change processing (such as, implement a newly written exit routine), start or stop a printer, or start diagnostic functions (such as the JES2 trace facility). Much of the processing can be changed without disrupting the remainder of the system. The following topics provide a brief overview of the control you have over JES2. (See z/OS JES2 Commands for an explanation of JES2 commands, and z/OS JES2 Messages for the text and explanation of JES2 messages.)