/sys$common/syshlp/helplib.hlb SET, ENTRY, Qualifiers, /LOG_FILE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /LOG_FILE[=filespec]
       /NOLOG_FILE

    Creates a log file with the specified file specification. You can
    specify a different device name, as long as the process executing
    the batch job has access to the device on which the log file will
    reside. Logical names in the file specification are translated in
    the context of the process that executes the SET ENTRY command.

    If you omit the /LOG_FILE qualifier and specify the /NAME
    qualifier, the log file is written to a file having the same file
    name as that specified by the /NAME qualifier; the file type is
    .LOG. When you omit the /LOG_FILE qualifier, the job-name value
    used with the /NAME qualifier must be a valid file name.