Hadoop调试：Exception in thread "main"java.lang.UnsatisfiedLinkError

• 异常完整描述

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

• 异常追踪信息如下：

java.lang.UnsatisfiedLinkError: org.apache.hadoop.io.nativeio.NativeIO$Windows.access0(Ljava/lang/String;I)Z
    at org.apache.hadoop.io.nativeio.NativeIO$Windows.access0(Native Method)
    at org.apache.hadoop.io.nativeio.NativeIO$Windows.access(NativeIO.java:609)
    at org.apache.hadoop.fs.FileUtil.canRead(FileUtil.java:980)
    at org.apache.hadoop.util.DiskChecker.checkAccessByFileMethods(DiskChecker.java:187)
    at org.apache.hadoop.util.DiskChecker.checkDirAccess(DiskChecker.java:174)
    at org.apache.hadoop.util.DiskChecker.checkDir(DiskChecker.java:108)
    at org.apache.hadoop.fs.LocalDirAllocator$AllocatorPerContext.confChanged(LocalDirAllocator.java:314)
    at org.apache.hadoop.fs.LocalDirAllocator$AllocatorPerContext.getLocalPathForWrite(LocalDirAllocator.java:377)
    at org.apache.hadoop.fs.LocalDirAllocator.getLocalPathForWrite(LocalDirAllocator.java:151)
    at org.apache.hadoop.fs.LocalDirAllocator.getLocalPathForWrite(LocalDirAllocator.java:132)
    at org.apache.hadoop.fs.LocalDirAllocator.getLocalPathForWrite(LocalDirAllocator.java:116)
    at org.apache.hadoop.mapred.LocalDistributedCacheManager.setup(LocalDistributedCacheManager.java:125)
    at org.apache.hadoop.mapred.LocalJobRunner$Job.<init>(LocalJobRunner.java:171)
    at org.apache.hadoop.mapred.LocalJobRunner.submitJob(LocalJobRunner.java:758)
    at org.apache.hadoop.mapreduce.JobSubmitter.submitJobInternal(JobSubmitter.java:244)
    at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1307)
    at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1304)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1920)
    at org.apache.hadoop.mapreduce.Job.submit(Job.java:1304)
    at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:1325)
    ……

• 该异常常见于windows环境中进行hadoop本地调试的场景

通过追踪信息可以找到问题发生源是由于NativeIO.java:609的access报错，代码如下：

 /**
     * Checks whether the current process has desired access rights on
     * the given path.
     * 
     * Longer term this native function can be substituted with JDK7
     * function Files#isReadable, isWritable, isExecutable.
     *
     * @param path input path
     * @param desiredAccess ACCESS_READ, ACCESS_WRITE or ACCESS_EXECUTE
     * @return true if access is allowed
     * @throws IOException I/O exception on error
     */
    public static boolean access(String path, AccessRight desiredAccess)
        throws IOException {
      return access0(path, desiredAccess.accessRight());
    }

可以看出是通过系统内核判断是否具有操作权限的判断功能，由于windows本身的权限设置此方法常会抛出异常。

• 解决方法1：临时测试修改源码

找到NativeIO的源码，在测试工程内建立同路径文件，复制全部代码，修改access方法如下所示：

   public static boolean access(String path, AccessRight desiredAccess)
        throws IOException {
        return true;
      //return access0(path, desiredAccess.accessRight());
    }

通过设置恒允许来跳过该问题。

• 解决方法2：使用远程linux集群协助调试

由于问题发生源是windows的关系，只需借助远程linux环境下的（或配置好的windows 环境）hadoop集群进行远程调试即可。
解决方法即为将远程环境的hadoop配置文件（如下）加入调试工程的环境变量中。

• core-site.xml
• hdfs-site.xml
• yarn-site.xml （非任务调试可无）
• mapred-site.xml （一般可无）