yarn map failed

Container launch failed for container_1385017085286_4943_01_000053 : org.apache.hadoop.yarn.exceptions.YarnException: Unauthorized request to start container.
 This token is expired. current time is 1386900106527 found 1386899991220 at sun.reflect.GeneratedConstructorAccessor20.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) 
at java.lang.reflect.Constructor.newInstance(Constructor.java:513) 
at org.apache.hadoop.yarn.api.records.impl.pb.SerializedExceptionPBImpl.instantiateException(SerializedExceptionPBImpl.java:152) 
at org.apache.hadoop.yarn.api.records.impl.pb.SerializedExceptionPBImpl.deSerialize(SerializedExceptionPBImpl.java:106) 
at org.apache.hadoop.mapreduce.v2.app.launcher.ContainerLauncherImpl$Container.launch(ContainerLauncherImpl.java:155) 
at org.apache.hadoop.mapreduce.v2.app.launcher.ContainerLauncherImpl$EventProcessor.run(ContainerLauncherImpl.java:369) 
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:662)

　　

datanode与namenode之间未设置时间同步，所以引起该异常。
解决方案：多个datanode与namenode进行时间同步。

时间同步：
在每台服务器的 /etc/crontab 中加入一行：
00 5 * * * root ntpdate cn.pool.ntp.org && hwclock -w