Intel® MPI Library User's Guide for Linux* OS
Hydra is a simplified, scalable process manager. Hydra will check for known resource managers to determine where the processes may be run and to distribute the processes among the targets using proxies on each host. These proxies will be used for process launching, cleanup, I/O forwarding, signal forwarding, and other tasks.
You can start Hydra by using mpiexec.hydra. See Scalable Process Management System (Hydra) Commands topic for a detailed list of options in the Intel® MPI Library Reference Manual.
Multipurpose daemon* (MPD) has been deprecated starting from Intel® MPI Library 5.0 release. To start parallel jobs, use the scalable process management system (Hydra).