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我正在关注 Tom White 的“Hadoop - The Definitive Guide”。当我尝试使用 Java 接口从 hadoop URL 读取数据时，我收到以下错误消息：

hadoop@ubuntu:/usr/local/hadoop$ hadoop URLCat hdfs://master/hdfs/data/SampleText.txt
12/11/21 13:46:32 INFO ipc.Client: Retrying connect to server: master/192.168.9.55:8020. Already tried 0 time(s).
12/11/21 13:46:33 INFO ipc.Client: Retrying connect to server: master/192.168.9.55:8020. Already tried 1 time(s).
12/11/21 13:46:34 INFO ipc.Client: Retrying connect to server: master/192.168.9.55:8020. Already tried 2 time(s).
12/11/21 13:46:35 INFO ipc.Client: Retrying connect to server: master/192.168.9.55:8020. Already tried 3 time(s).
12/11/21 13:46:36 INFO ipc.Client: Retrying connect to server: master/192.168.9.55:8020. Already tried 4 time(s).
12/11/21 13:46:37 INFO ipc.Client: Retrying connect to server: master/192.168.9.55:8020. Already tried 5 time(s).

URLCat 文件的内容如下：

import java.net.URL;
import java.io.InputStream;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.fs.FsUrlStreamHandlerFactory;

public class URLCat {
static {
    URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());
}

public static void main(String[] args) throws Exception {
    InputStream in = null;
    try {
        in = new URL(args[0]).openStream();
        IOUtils.copyBytes(in, System.out, 4096, false);
    } finally {
        IOUtils.closeStream(in);
    }
}
}

/etc/hosts 文件内容为：

127.0.0.1   localhost
127.0.1.1   ubuntu.ubuntu-domain    ubuntu

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

# /ect/hosts Master and slaves
192.168.9.55    master
192.168.9.56    slave1
192.168.9.57    slave2
192.168.9.58    slave3
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1 回答 1

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首先，我会检查 Hadoop 守护进程是否正在运行。一个方便的工具是jps。确保（至少）名称节点和数据节点正在运行。

如果仍然无法连接，请检查 url 是否正确。正如您提供的hdfs://master/（没有任何端口号）Hadoop 假设您的名称节点侦听端口8020（默认）。这就是您在日志中看到的内容。

For a quick lookup in core-site.xml (fs.default.name) you can check whether you have a custom port defined for the filesystem URI (in this case 54310).

于 2012-11-21T12:06:23.927 回答