Naming your subsystem

The name you use for your subsystems depends on how your subsystem is defined to MVS™. Use one of the following naming conventions:

If your subsystem is defined to MVS through the IEFSSNxx parmlib member processing at IPL, the subsystem name can be no more than four characters long, beginning with an alphabetic character or #, @ or $. The remaining characters can be alphabetic, numeric, or #, @, or $.
If your subsystem is defined to MVS through the IEFSSI macro, the subsystem name can be no more than four characters long, containing any character other than blanks or nulls.
If you subsystem is defined to MVS through the SETSSI command, the subsystem name can contain any character other than blanks or nulls that is valid for system commands. See z/OS MVS System Commands for more information on the valid characters.

You cannot use the following names for your subsystems:

APPC
ASCH
MSTR
OMVS
STC
SYS
TSO

Use a meaningful name for your subsystem to facilitate debugging. Also, check for the subsystem names that are currently in use by IBM-supplied and vendor-supplied products.

Note: Since subsystems can be added after IPL, it is difficult to determine which unique name to use for a subsystem. You can use the query request of the IEFSSI macro to find the names of existing subsystems to ensure that your subsystem name is unique.