aeron-client/src/main/java/io/aeron/CommonContext.java
public MappedByteBuffer mapExistingCncFile(final Consumer<String> logger)
    {
        final File cncFile = new File(aeronDirectory, CncFileDescriptor.CNC_FILE);

        if (cncFile.exists() && cncFile.length() > 0)
        {
            if (null != logger)
            {
                logger.accept("INFO: Aeron CnC file exists: " + cncFile);
            }

            return IoUtil.mapExistingFile(cncFile, CncFileDescriptor.CNC_FILE);
        }

        return null;
    }
public MappedByteBuffer mapExistingCncFile(final Consumer<String> logger)
    {
        final File cncFile = new File(aeronDirectory, CncFileDescriptor.CNC_FILE);

        if (cncFile.exists() && cncFile.length() > 0)
        {
            if (null != logger)
            {
                logger.accept("INFO: Aeron CnC file exists: " + cncFile);
            }

            return IoUtil.mapExistingFile(cncFile, CncFileDescriptor.CNC_FILE);
        }

        return null;
    }
Map the CnC file if it exists.

@param logger for feedback
@return a new mapping for the file if it exists otherwise null;