using SFLRCDNBR we can retrive RRN through rpg

Using *PSSR routine.
Declare a *PSSR rouine as a subroutine and write the code u need to handle the error.

Before using GDG , We need to create GDG index and model. 
IDCAMS (the 'AMS' stands for Access Method Services), utility is used to create GDG index.
Once the index has  been  created,  a  model data set must be created. This  model data set contains specifications for the DCB subparameters for all data sets that will belong to that GDG. Programmer can override this default values if he want.

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JCLLIB is a JCL stmt that allows the user to specify his/her own proclibs and/or specify the order in which
they're searched to find the PROC(s) or INCLUDE libraries invoked in the JCL

A procedure that you catalog in a library is called a cataloged procedure.
A cataloged procedure may consist of these JCL statements:
CNTL, command, DD, ENDCNTL, EXEC, IF/THEN/ELSE/ENDIF, INCLUDE, OUTPUT JCL, and SET. Optionally, a cataloged procedure can begin with a PROC statement and end with a PEND statement. If coded, PROC must be the first statement in the procedure.
The library containing cataloged procedures is a partitioned data set (PDS) or a partitioned data set
extended (PDSE). The system procedure library is SYS1.PROCLIB. The installation can have many more procedure libraries with different names. You can also have procedures in a private library. The name of a cataloged procedure is its member name or alias in the library.
When a cataloged procedure is called, the calling step receives a copy of the procedure; therefore, a cataloged procedure can be used simultaneously by more than one job.