ElasticSearch 5.0 不能使用root启动源码分析

Elasticsearch自从升级到2.x之后便有提示“谨慎使用root用户启动”，但是我们通过简单的配置还是可以使用root启动的。以Elasticsearch 2.3源码为例，Elasticsearch在启动时需要初始化Native资源，Native资源的初始化是通过Bootstrap中initializeNatives方法进行的，下面是源码：

/** initialize native resources */
    public static void initializeNatives(Path tmpFile, boolean mlockAll, boolean seccomp, boolean ctrlHandler) {
        final ESLogger logger = Loggers.getLogger(Bootstrap.class);

        // check if the user is running as root, and bail
        if (Natives.definitelyRunningAsRoot()) {
            if (Boolean.parseBoolean(System.getProperty("es.insecure.allow.root"))) {
                logger.warn("running as ROOT user. this is a bad idea!");
            } else {
                throw new RuntimeException("don't run elasticsearch as root.");
            }
        }

        // enable secure computing mode
        if (seccomp) {
            Natives.trySeccomp(tmpFile);
        }

        // mlockall if requested
        if (mlockAll) {
            if (Constants.WINDOWS) {
               Natives.tryVirtualLock();
            } else {
               Natives.tryMlockall();
            }
        }

        // listener for windows close event
        if (ctrlHandler) {
            Natives.addConsoleCtrlHandler(new ConsoleCtrlHandler() {
                @Override
                public boolean handle(int code) {
                    if (CTRL_CLOSE_EVENT == code) {
                        logger.info("running graceful exit on windows");
                        Bootstrap.stop();
                        return true;
                    }
                    return false;
                }
            });
        }

        // force remainder of JNA to be loaded (if available).
        try {
            JNAKernel32Library.getInstance();
        } catch (Throwable ignored) {
            // we've already logged this.
        }

        // init lucene random seed. it will use /dev/urandom where available:
        StringHelper.randomId();
    }

可以看到代码中有检查当前用户是否为root用户的操作，如果在系统环境变量中配置了es.insecure.allow.root为true，则可以使用root用户运行，否则抛出异常。

// check if the user is running as root, and bail
        if (Natives.definitelyRunningAsRoot()) {
            if (Boolean.parseBoolean(System.getProperty("es.insecure.allow.root"))) {
                logger.warn("running as ROOT user. this is a bad idea!");
            } else {
                throw new RuntimeException("don't run elasticsearch as root.");
            }
        }

在elasticsearch 5.0中同样有判断启动用户的操作，但是这次彻底禁止了使用root用户启动，代码如下：

    /** initialize native resources */
    public static void initializeNatives(Path tmpFile, boolean mlockAll, boolean systemCallFilter, boolean ctrlHandler) {
        final Logger logger = Loggers.getLogger(Bootstrap.class);

        // check if the user is running as root, and bail
        if (Natives.definitelyRunningAsRoot()) {
            throw new RuntimeException("can not run elasticsearch as root");
        }

        // enable system call filter
        if (systemCallFilter) {
            Natives.tryInstallSystemCallFilter(tmpFile);
        }

        // mlockall if requested
        if (mlockAll) {
            if (Constants.WINDOWS) {
               Natives.tryVirtualLock();
            } else {
               Natives.tryMlockall();
            }
        }

        // listener for windows close event
        if (ctrlHandler) {
            Natives.addConsoleCtrlHandler(new ConsoleCtrlHandler() {
                @Override
                public boolean handle(int code) {
                    if (CTRL_CLOSE_EVENT == code) {
                        logger.info("running graceful exit on windows");
                        try {
                            Bootstrap.stop();
                        } catch (IOException e) {
                            throw new ElasticsearchException("failed to stop node", e);
                        }
                        return true;
                    }
                    return false;
                }
            });
        }

        // force remainder of JNA to be loaded (if available).
        try {
            JNAKernel32Library.getInstance();
        } catch (Exception ignored) {
            // we've already logged this.
        }

        Natives.trySetMaxNumberOfThreads();
        Natives.trySetMaxSizeVirtualMemory();

        // init lucene random seed. it will use /dev/urandom where available:
        StringHelper.randomId();
    }

可以发现还是通过Natives.definitelyRunningAsRoot()方法来检查当前启动用户是否为root用户，但是与2.3版本不同的是，这次彻底禁止了使用root用户启动，因为代码中我们找不到检查配置root用户启动的部分：

if (Natives.definitelyRunningAsRoot()) {
            throw new RuntimeException("can not run elasticsearch as root");
        }

如果判断为使用root用户，elasticsearch直接抛出运行时异常。