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

       /SYSTEM
       /NOSYSTEM

    Controls whether the names of installed files and files opened
    by the system are displayed. Files opened by the system are those
    that have been opened without the use of an ancillary control
    process (ACP), such as INDEXF.SYS and QUOTA.SYS.

    If you specify the /NOSYSTEM qualifier with the /FILES qualifier,
    only files opened by processes are displayed. If you omit both
    the /SYSTEM and /NOSYSTEM qualifiers and specify the /FILES
    qualifier, the names of all files currently open on the system
    are displayed.

    You can use this qualifier only with the /FILES qualifier. See
    the description of the /FILES qualifier for more details.