VMS Help RTL Routines, LIB$, LIB$ATTACH, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 process-id

    OpenVMS usage:process_id
    type:         longword integer (unsigned)
    access:       read only
    mechanism:    by reference

    Identification of the process to which LIB$ATTACH requests the
    calling process to attach its terminal. The process-id argument
    is the address of an unsigned longword integer containing the
    process identification. The specified process must be currently
    detached (by means of a SPAWN or ATTACH command or by a call to
    LIB$SPAWN or LIB$ATTACH) and must be part of the caller's job.