@Nullable
        private static String normalizeHostname(String line) {
            final String hostname = IDN.toASCII(line.trim(), IDN.ALLOW_UNASSIGNED);
            if (!HOSTNAME_PATTERN.matcher(hostname).matches()) {
                return null;
            }
            return Ascii.toLowerCase(hostname);
        }
Returns {@code true} if the operating system is Linux.
core/src/main/java/com/linecorp/armeria/common/util/SystemInfo.java