InterSystems FAQ rubric
If you want to run an OS executable file, command, or a program created within an InterSystems product when the InterSystems product starts, write the processing in the SYSTEM^%ZSTART routine. (The %ZSTART routine is created in the %SYS namespace).
Before you write any code in SYSTEM^%ZSTART, make sure that it works properly under all conditions.
If the ^%ZSTART routine is written incorrectly, or if it is written correctly but the command does not return a response or an error occurs during processing, InterSystems products may not be able to start.