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

       /TRUNCATE_USER_NAME
       /NOTRUNCATE_USER_NAME

    Optional. Default: /NOTRUNCATE_USER_NAME.

    Abbreviates the user name sent to the remote host to eight
    characters (required for older UNIX hosts, which limit user names
    to eight characters).