hdfs nfs gateway mount.nfs:输入/输出错误？
1.错误如下：

[root@xx sbin]# mount -t nfs -o vers=3,proto=tcp,nolock,noacl,sync localhost:/ /hdfs_y
mount.nfs: Input/output error

2016-03-10 15:12:06,350 WARN org.apache.hadoop.hdfs.nfs.nfs3.RpcProgramNfs3: Exception
804 org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.security.authorize.AuthorizationException): User: hadoop is not allowed to impersonate root
805 at org.apache.hadoop.ipc.Client.call(Client.java:1475)
......

2.hadoop的进程，用户“hadoop”启动hadoop。

[root@WEB-W031 sbin]# jps
6755 Nfs3
11199 Jps
6163 Portmap
7977 SecondaryNameNode
7720 NameNode
8217 ResourceManager
16762 org.eclipse.equinox.launcher_1.3.0.v20130327-1440.jar

[hadoop@WEB-W031 hadoop]$ jps
6755 Nfs3
7977 SecondaryNameNode
7720 NameNode
8217 ResourceManager
11239 Jps
You have new mail in /var/spool/mail/root

3.参考：https://hadoop.apache.org/docs/r2.7.2/hadoop-project-dist/hadoop-hdfs/hdfsnfsgateway.html#allow_mounts_from_unprivileged_clients
非常感谢！