VMS Help DTM, ATTACH, Command Qualifiers, /PARENT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

   Specifies that the process you want to attach to is your original
   (parent) process.

   If you specify the /PARENT qualifier, do not specify the process
   name parameter or the /IDENTIFICATION qualifier. If you do not
   specify a qualifier, you must specify a process name.