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 new with CICS TS 1.3 and it permits code to be executed under its own TCB rather than CICS' Quasi- Reentrant TCB. Initially, this new facility will be use 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 with all the other system header files.


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