报错背景：
CDH集成了Flume服务，准备通过Flume将kafka中的数据放到HDFS中，
启动Flume的时候报错。
报错现象：
// :: INFO hdfs.HDFSDataStream: Serializer = TEXT, UseRawLocalFileSystem = false
// :: INFO hdfs.BucketWriter: Creating hdfs://master:8020/yk/dl/alarm_his/AlarmHis.1557281724769.txt.tmp
// :: WARN hdfs.HDFSEventSink: HDFS IO error
org.apache.hadoop.security.AccessControlException: Permission denied: user=root, access=WRITE, inode="/yk/dl/alarm_his":hdfs:supergroup:drwxr-xr-x
at org.apache.hadoop.hdfs.server.namenode.DefaultAuthorizationProvider.checkFsPermission(DefaultAuthorizationProvider.java:)
at org.apache.hadoop.hdfs.server.namenode.DefaultAuthorizationProvider.check(DefaultAuthorizationProvider.java:)
at org.apache.hadoop.hdfs.server.namenode.DefaultAuthorizationProvider.check(DefaultAuthorizationProvider.java:)
at org.apache.hadoop.hdfs.server.namenode.DefaultAuthorizationProvider.checkPermission(DefaultAuthorizationProvider.java:)
at org.apache.hadoop.hdfs.server.namenode.FSPermissionChecker.checkPermission(FSPermissionChecker.java:)
at org.apache.hadoop.hdfs.server.namenode.FSDirectory.checkPermission(FSDirectory.java:)
at org.apache.hadoop.hdfs.server.namenode.FSDirectory.checkPermission(FSDirectory.java:)
at org.apache.hadoop.hdfs.server.namenode.FSDirectory.checkAncestorAccess(FSDirectory.java:)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.checkAncestorAccess(FSNamesystem.java:)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFileInternal(FSNamesystem.java:)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFileInt(FSNamesystem.java:)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFile(FSNamesystem.java:)
at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.create(NameNodeRpcServer.java:)
at org.apache.hadoop.hdfs.server.namenode.AuthorizationProviderProxyClientProtocol.create(AuthorizationProviderProxyClientProtocol.java:)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.create(ClientNamenodeProtocolServerSideTranslatorPB.java:)
at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$.callBlockingMethod(ClientNamenodeProtocolProtos.java)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:)
at org.apache.hadoop.ipc.Server$Handler$.run(Server.java:)
at org.apache.hadoop.ipc.Server$Handler$.run(Server.java:)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:)
at java.lang.reflect.Constructor.newInstance(Constructor.java:)
at org.apache.hadoop.ipc.RemoteException.instantiateException(RemoteException.java:)
at org.apache.hadoop.ipc.RemoteException.unwrapRemoteException(RemoteException.java:)
at org.apache.hadoop.hdfs.DFSOutputStream.newStreamForCreate(DFSOutputStream.java:)
at org.apache.hadoop.hdfs.DFSClient.create(DFSClient.java:)
at org.apache.hadoop.hdfs.DFSClient.create(DFSClient.java:)
at org.apache.hadoop.hdfs.DistributedFileSystem$.doCall(DistributedFileSystem.java:)
at org.apache.hadoop.hdfs.DistributedFileSystem$.doCall(DistributedFileSystem.java:)
at org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:)
at org.apache.hadoop.hdfs.DistributedFileSystem.create(DistributedFileSystem.java:)
at org.apache.hadoop.hdfs.DistributedFileSystem.create(DistributedFileSystem.java:)
at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:)
at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:)
at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:)
at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:)
at org.apache.flume.sink.hdfs.HDFSDataStream.doOpen(HDFSDataStream.java:)
at org.apache.flume.sink.hdfs.HDFSDataStream.open(HDFSDataStream.java:)
at org.apache.flume.sink.hdfs.BucketWriter$.call(BucketWriter.java:)
at org.apache.flume.sink.hdfs.BucketWriter$.call(BucketWriter.java:)
at org.apache.flume.sink.hdfs.BucketWriter$$.run(BucketWriter.java:)
at org.apache.flume.auth.SimpleAuthenticator.execute(SimpleAuthenticator.java:)
at org.apache.flume.sink.hdfs.BucketWriter$.call(BucketWriter.java:)
at java.util.concurrent.FutureTask.run(FutureTask.java:)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:)
at java.lang.Thread.run(Thread.java:)
报错原因：
根据日志信息可以解读出，root用户想要在文件系统里面创建一个目录，失败。
原因是，root用户无法操作hdfs
报错解决：
重启HDFS即可