How z/OS UNIX System Services interact with the MVS subsystems

People who are porting apps to z/OS often ask how z/OS UNIX System Services interact with the "subsystems". When running in a z/OS UNIX environment, a process is running on a task in an address space. The services for

  • CICS
  • IMS
  • DB2
  • WebSphere MQ
  • CPI-C

are all MVS-enabled services, so, for the most part, they are completely unaware of whether a process is a batch job or a forked UNIX process.

The following are brief statements about the interaction between z/OS UNIX and some z/OS subsystems and elements. For more details, see the z/OS XL C/C++ Programming Guide , and, particularly, the library for the subsystem or element.


For CICS, you can use EXCI (External Call Interface) to request a CICS service from a UNIX process, but at this time you cannot invoke UNIX services from within a CICS transaction.

OTE is with CICS TS 1.3 and it permits code to be executed under its own TCB rather than CICS' Quasi- Reentrant TCB. Initially, this facility will be used for Java applications, but the long-term intent is to permit other applications to directly invoke MVS and/or UNIX services without disrupting traditional CICS processing.


For IMS, you can request the IMS service from a UNIX process by using the APPC interface to IMS. You can run a UNIX program as an IMS transaction.

From the WebSphere Application Server (or Lotus Domino Go Webserver), a process can connect with IMS Connect, then OTMA, then IMS and back again. The Redbook IMS e-Business Connect Using the IMS Connectors,, SG24-5427, describes how to connect your IMS systems to an Internet server using IMS Connect and either IMS Web Studio or user-developed Java applications.

DB2 for z/OS

DB2 for z/OS is accessible from a z/OS UNIX process.

WebSphere MQ

WebSphere MQ API calls can be made from z/OS and OS/390 UNIX applications. WebSphere MQ treats these programs as batch applications.


The APPC CPI-C services have been available to C programs and continue to be available to UNIX processes. At first, APPC header files were shipped in SYS1.SAMPLIB, but now they install in the hierarchical file system.


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