For most z/OS UNIX applications, the Language Environment® runtime library (SCEERUN and SCEERUN2) is needed. The SCEERUN and SCEERUN2 data sets can be placed in LNKLST or accessed via STEPLIB. (A STEPLIB is a set of private libraries used to store a new or test version of an application program, such as a new version of a runtime library.)

Placing the Language Environment runtime library (SCEERUN and SCEERUN2) in LNKLST requires the least amount of setup. If this method is used, then consider placing the SCEELPA data set (which contains key modules) in LPA for better performance. See Improving performance of runtime routines.

However, sometimes the SCEERUN data set cannot be placed in LNKLST, because other applications require the pre-Language Environment runtime libraries. In that case, you can make the Language Environment runtime library available through STEPLIB as described in Steps for making the runtime library available through STEPLIB. In addition, you can use this approach to test new levels of the runtime libraries.