This guide describes the facilities of REACT real-time for Linux. A real-time program is one that must maintain a fixed timing relationship to external hardware. In order to respond to the hardware quickly and reliably, a real-time program must have special support from the system software and hardware. This guide discusses how Linux and REACT support real-time programs, controlling CPU workload, using the frame scheduler, optimizing disk I/O, using PCI devices, generating a REACT system configuration, and using the SGI Linux Trace feature. It also provides installation and troubleshooting information.