code: public static void showVersion(BootstrapConfig bootProps) {
          BootstrapManifest bootManifest;
          try {
              bootManifest = BootstrapManifest.readBootstrapManifest(Boolean.parseBoolean(bootProps.get(BootstrapConstants.LIBERTY_BOOT_PROPERTY)));
              String kernelVersion = bootManifest.getBundleVersion();
              String productInfo = getProductInfoDisplayName();
  
              processVersion(bootProps, "info.serverVersion", kernelVersion, productInfo, true);
          } catch (IOException e) {
              throw new LaunchException("Could not read the jar manifest", BootstrapConstants.messages.getString("error.unknown.kernel.version"), e);
          }
      }
docs: Get the runtime build version based on the information in the manifest of the
  kernel jar: this is not authoritative, as it won't include information about
  applied iFixes, etc.