src/Pure/System/isabelle_system.scala

     clean: Boolean = false,
     args: List[String] = Nil
   ): Process_Result = {
     val script =
       "rsync --protect-args --archive" +
-        (if (verbose) " --verbose" else "") +
+        (if (verbose || dry_run) " --verbose" else "") +
         (if (dry_run) " --dry-run" else "") +
         (if (clean) " --delete-excluded" else "") +
         (if (args.nonEmpty) " " + Bash.strings(args) else "")
     progress.bash(script, cwd = cwd, echo = true)
   }