hadoop dfsadmin -safemode leave 有两个方法离开这种安全模式 1. 修改dfs.safemode.threshold.pct为一个比较小的值，缺省是0.999。 2. hadoop dfsadmin -safemode leave命令强制离开 http://bbs.hadoopor.com/viewthread.php?tid=61&extra=page=1 －－－－－－－－－－－－－－－－－－－－－－－－－－－－－ Safe mode is exited when the minimal replication condition is reached, plus an extension time of 30 seconds. The minimal replication condition is when 99.9% of the blocks in the whole filesystem meet their minimum replication level (which defaults to one, and is set by dfs.replication.min). 安全模式的退出前提 - 整个文件系统中的99.9%（默认是99.9%，可以通过dfs.safemode.threshold.pct设置）的Blocks达到最小备份级别(默认是1，可以通过dfs.replication.min设置)。 dfs.safemode.threshold.pctSetting this value to 0 or less forces the name-node not to start in safe mode. Setting this value to more than 1 means the namenode never exits safe mode. －－－－－－－－－－－－－－－－－－－－－－－－－－－－－ 用户可以通过dfsadmin -safemode value float 0.999 The proportion of blocks in the system that must meet the minimum replication level defined by dfs.rep lication.min before the namenode will exit safe mode. 来操作安全模式，参数value的说明如下： enter - 进入安全模式 leave - 强制NameNode离开安全模式 get - 返回安全模式是否开启的信息 wait - 等待，一直到安全模式结束。 ps1: ERROR security.UserGroupInformation: PriviledgedActionException as:root cause:org.apache.hadoop.ipc.RemoteException: java.io.IOException: java.lang.NullPointerException