IBM Mainframe Forum

In below JCL STEP, could any one please explain what is DYNAMNBR parameter and why it is used?

STEP001 EXEC PGM=IKJEFT1B,DYNAMNBR=500

Thanks

Hi, as far as I understand it, the DYNAMNBR is used when a program dynamically allocates datasets, that is where the dataset is not specified in a DD card, perhaps for sort work files etc. The number should be an estimated number of dynamically allocated datasets plus the number specified in DD statements. If this number is exceeded then your job will fail. 500 seems to be plenty though!

Thanks very much for the info.

Could you please explain me what do you mean by dynamically allocation of datasets?
Could you please explain with an example.

Thanks in advance.

Suppose your step is doing an FTP. The FTP program reads the input statements and finds the file name you wish to send/receive. The program does dynamic allocation to associate the file with a DDname. Now the program can do an OPEN of the DDname and read/write records. It appears to the system just like you had added the DDname to your step, like STEPLIB or SYSPRINT.

Many programs under TSO do dynamic allocation. ISPF EDIT, library utilities and others all dynamically allocate the files you specify on the panels. If you do a TSO command LISTALC STATUS in option 6 you'll see files allocated that are not in your LOGON PROC.