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

• 異常完整描述

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

• 異常追蹤信息如下：

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)
    ……

• 該異常常見於windows環境中進行hadoop本地調試的場景

通過追蹤信息可以找到問題發生源是由於NativeIO.java:609的access報錯，代碼如下：

 /**
     * 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());
    }

可以看出是通過系統內核判斷是否具有操作權限的判斷功能，由於windows本身的權限設置此方法常會拋出異常。

• 解決方法1：臨時測試修改源碼

找到NativeIO的源碼，在測試工程內建立同路徑文件，複製全部代碼，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());
    }

通過設置恆允許來跳過該問題。

• 解決方法2：使用遠程linux集羣協助調試

由於問題發生源是windows的關係，只需藉助遠程linux環境下的（或配置好的windows 環境）hadoop集羣進行遠程調試即可。
解決方法即爲將遠程環境的hadoop配置文件（如下）加入調試工程的環境變量中。

• core-site.xml
• hdfs-site.xml
• yarn-site.xml （非任務調試可無）
• mapred-site.xml （一般可無）