private void openCtlFile() {
        if (ctlFile != null) {
            // already done this
            return;
        }
        if (logControlFilename == null) {
            // System.err.println("initialize limit to: "+defaultLevelCtrl.getLevelLimit());
            Logger.getLogger("").setLevel(defaultLevelCtrl.getLevelLimit());
            // only default level controller, very little can be done
            return;
        }

        try {
            ctlFile = new RandomAccessFile(logControlFilename, "rw");
            ctlFileAppender = new FileOutputStream(logControlFilename, true);
            ensureHeader();
            extendMapping();

            if (checkBackRunner == null) {
                checkBackRunner = new CheckBackRunner();
                LogSetup.getTaskRunner().schedule(checkBackRunner, 1000, 2999);
            }
        } catch (java.io.IOException e) {
            System.err.println("problem opening logcontrol file "
                               +logControlFilename+": "+e);
            resetCtlFile();
        }
    }
level controller for default levels (first-time logging
or logging without a logcontrol file)
vespalog/src/main/java/com/yahoo/log/VespaLevelControllerRepo.java