org.apache.Hadoop.ipc.RemoteException: org.apache.hadoop.hdfs.server.namenode.SafeModeException: Cannot delete /tmp/hadoop/mapred/system. Name node is in safe mode.
The ratio of reported blocks 0.7857 has not reached the threshold 0.9990. Safe mode will be turned off automatically.
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.deleteInternal(FSNamesystem.java:1992)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.delete(FSNamesystem.java:1972)
at org.apache.hadoop.hdfs.server.namenode.NameNode.delete(NameNode.java:792)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:563)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1388)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1384)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1083)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1382)
请不要急，NameNode会在开始启动阶段自动关闭安全模式，然后启动成功。如果你不想等待，可以运行：
bin/hadoop dfsadmin -safemode leave 强制结束。