VMS Help SHOW, LOGICAL, Qualifiers, /SYSTEM  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Indicates that only the system logical name table is to
    be searched. The /SYSTEM qualifier is synonymous with the
    /TABLE=LNM$SYSTEM qualifier. If you specify the /SYSTEM qualifier
    and you do not also specify a logical name, all names in the
    system table are displayed.