The D OMVS command is a UNIX System Services command used to display and diagnose current OMVS-based settings and associated processes, such as file structures, applications, user services, and servers. D OMVS is usually referred to as UNIX System Services or USS, and runs as a started task under MVS with a default name of BPXOINIT. Many operations have chosen to initiate some or most of their TCP/IP ‘stack-based’ tasks via USS, including the FTP Daemon (FTPD). Default allocations are made in a Parmlib member for USS (BPXPRMxx), in the same way as in other major MVS subsystems. Maximum values or limits are set for resource types such as the maximum number of concurrent processes (MAXPROCSYS) and the maximum number of concurrent threads (MAXTHREADS).
USS values may apply system-wide or specifically for any single USS-based process. Occasionally these values can reach critical mass and will no longer operate properly as a result. A specific process may not behave properly at other times as well. Because USS is so tightly woven with TCP/IP, this behavior can significantly impact the stability of the TCP/IP stack as well. USS must have at least one Common INET (CINET) routing transport link reachable in order for it to communicate with TCP/IP. Because of this, efficient, proactive use of the D OMVS command may uncover some of these potential problems and corrective action can be taken to alleviate the situation, such as modifying OMVS settings with the SETOMVS command.
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