Could not locate executable null 解决办法

问题导读：

1.建一个MapReduce Project，运行时发现出问题：Could not locate executable null，该如何解决？
2.Could not locate executabl   ....\hadoop-2.2.0\hadoop-2.2.0\bin\winutils.exe in the Hadoop binaries.该如何解决？

1.创建一个MapReduce Project，运行时发现出问题了。

java.io.IOException: Could not locate executable null\bin\winutils.exe in the Hadoop binaries.

跟代码就去发现是HADOOP_HOME的问题。如果HADOOP_HOME为空，必然fullExeName为null\bin\winutils.exe。解决方法很简单啦，乖乖的配置环境变量吧，不想重启电脑可以在MapReduce程序里加上System.setProperty("hadoop.home.dir", "...");暂时缓缓。

org.apache.hadoop.util.Shell.java

  public static final String getQualifiedBinPath(String executable)
  throws IOException {
    // construct hadoop bin path to the specified executable
    String fullExeName = HADOOP_HOME_DIR + File.separator + "bin"
      + File.separator + executable;

    File exeFile = new File(fullExeName);
    if (!exeFile.exists()) {
      throw new IOException("Could not locate executable " + fullExeName
        + " in the Hadoop binaries.");
    }

    return exeFile.getCanonicalPath();
  }

private static String HADOOP_HOME_DIR = checkHadoopHome();
private static String checkHadoopHome() {

    // first check the Dflag hadoop.home.dir with JVM scope
    String home = System.getProperty("hadoop.home.dir");

    // fall back to the system/user-global env variable
    if (home == null) {
      home = System.getenv("HADOOP_HOME");
    }
     ...
}

2.这个时候得到完整的地址fullExeName，我机器上是D:\Hadoop\tar\hadoop-2.2.0\hadoop-2.2.0\bin\winutils.exe。继续执行代码又发现了错误

Could not locate executable D:\Hadoop\tar\hadoop-2.2.0\hadoop-2.2.0\bin\winutils.exe in the Hadoop binaries.

就去一看，没有winutils.exe这个东西。去https://github.com/srccodes/hadoop-common-2.2.0-bin下载一个，放就去即可。
3.继续出问题

1. at org.apache.hadoop.util.Shell.execCommand(Shell.java:661)at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:639)at org.apache.hadoop.fs.RawLocalFileSystem.mkdirs(RawLocalFileSystem.java:435)

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继续跟代码org.apache.hadoop.util.Shell.java

1. <span style="line-height: 1.5;"> </span> public static String[] getSetPermissionCommand(String perm, boolean recursive,
2. String file) {
3. String[] baseCmd = getSetPermissionCommand(perm, recursive);
4. String[] cmdWithFile = Arrays.copyOf(baseCmd, baseCmd.length + 1);
5. cmdWithFile[cmdWithFile.length - 1] = file;
6. return cmdWithFile;
7. }
8. /** Return a command to set permission */
9. public static String[] getSetPermissionCommand(String perm, boolean recursive) {
10. if (recursive) {
11. return (WINDOWS) ? new String[] { WINUTILS, "chmod", "-R", perm }
12. : new String[] { "chmod", "-R", perm };
13. } else {
14. return (WINDOWS) ? new String[] { WINUTILS, "chmod", perm }
15. : new String[] { "chmod", perm };
16. }
17. }

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cmdWithFile数组的内容为{"D:\Hadoop\tar\hadoop-2.2.0\hadoop-2.2.0\bin\winutils.exe", "chmod", "755", "xxxfile"}，我把这个单独在cmd里执行了一下，发现

无法启动此程序，因为计算机中丢失 MSVCR100.dll

那就下载一个呗http://files.cnblogs.com/sirkevin/msvcr100.rar，丢到C:\Windows\System32里面。再次cmd执行，又来了问题

应用程序无法正常启动(0xc000007b)

下载http://blog.csdn.net/vbcom/article/details/7245186 DirectX_Repair来解决这个问题吧。记得修复完后要重启电脑。搞定后cmd试一下，很棒。
4.到了这里，已经看到曙光了，但问题又来了

Exception in thread "main" java.lang.UnsatisfiedLinkError: org.apache.hadoop.io.nativeio.NativeIO$Windows.access0(Ljava/lang/String;I)Z

代码就去

1. /** Windows only method used to check if the current process has requested*  access rights on the given path. */
2. private static native boolean access0(String path, int requestedAccess);

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显然缺少dll文件，还记得https://github.com/srccodes/hadoop-common-2.2.0-bin下载的东西吧，里面就有hadoop.dll，最好的方法就是用hadoop-common-2.2.0-bin-master/bin目录替换本地hadoop的bin目录，并在环境变量里配置PATH=HADOOP_HOME/bin，重启电脑。
1.下载地址

 
hadoop家族、strom、spark、Linux、flume等jar包、安装包汇总下载(持续更新)

注意的问题：
环境变量一定配置正确，否则还是不能运行
PATH=HADOOP_HOME/bin，如果这个不行，可以换成绝对路径

5.终于看到了MapReduce的正确输出output99。

总结

• hadoop eclipse插件不是必须的，其作用在我看来就是如下三点(这个是一个错误的认识，具体请参考http://zy19982004.iteye.com/blog/2031172)。study-hadoop是一个普通project，直接运行(不通过Run on Hadoop这只大象)，一样可以调试到MapReduce。
  • 对hadoop中的文件可视化。
  • 创建MapReduce Project时帮你引入依赖的jar。
  • Configuration conf = new Configuration();时就已经包含了所有的配置信息。
• 还是自己下载hadoop2.2的源码编译好，应该是不会有任何问题的(没有亲测)。

六. 其它问题

• 还是
  1. Exception in thread "main" java.lang.UnsatisfiedLinkError: org.apache.hadoop.io.nativeio.NativeIO$Windows.access0(Ljava/lang/String;I)Z

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  代码跟到org.apache.hadoop.util.NativeCodeLoader.java去看

  1. static {
  2. // Try to load native hadoop library and set fallback flag appropriately
  3. if(LOG.isDebugEnabled()) {
  4. LOG.debug("Trying to load the custom-built native-hadoop library...");
  5. }
  6. try {
  7. System.loadLibrary("hadoop");
  8. LOG.debug("Loaded the native-hadoop library");
  9. nativeCodeLoaded = true;
  10. } catch (Throwable t) {
  11. // Ignore failure to load
  12. if(LOG.isDebugEnabled()) {
  13. LOG.debug("Failed to load native-hadoop with error: " + t);
  14. LOG.debug("java.library.path=" +
  15. System.getProperty("java.library.path"));
  16. }
  17. }
  18. if (!nativeCodeLoaded) {
  19. LOG.warn("Unable to load native-hadoop library for your platform... " +
  20. "using builtin-java classes where applicable");
  21. }
  22. }

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  这里报错如下

  1. DEBUG org.apache.hadoop.util.NativeCodeLoader - Failed to load native-hadoop with error: java.lang.UnsatisfiedLinkError: HADOOP_HOME\bin\hadoop.dll: Can‘t load AMD 64-bit .dll on a IA 32-bit platform

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  怀疑是32位jdk的问题，替换成64位后，没问题了

  1. 2014-03-11 19:43:08,805 DEBUG org.apache.hadoop.util.NativeCodeLoader - Trying to load the custom-built native-hadoop library...
  2. 2014-03-11 19:43:08,812 DEBUG org.apache.hadoop.util.NativeCodeLoader - Loaded the native-hadoop library

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  这里也解决了一个常见的警告

  1. WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable

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