问题描述：
在Ambari中启动HDFS中namenode时出现404 - Retrying after 10 seconds. Reason: Execution of '/usr/hdp/current/hadoop-hdfs-namenode/bin/hdfs dfsadmin -fs hdfs://master:8020 -safemode get | grep 'Safe mode is OFF'' returned 1.错误
解决方法：
# su hdfs //切换到hdfs用户，ambari默认HDFS最高权限用户是hdfs
# hadoop dfsadmin -safemode leave //离开安全模式