ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: All directories in dfs.data.dir are invalid

几天前配置好了hadoop1.2.1，一直好好的。自从更改了core-site.xml中的hadoop.tmp.dir为/home/caiyong/hadoop_tmp后，启动hadoop，jps查看只有5个进程，DataNode始终不见，重启了几次还是看不到DataNode进程。查看日志发现如下错误：

2015-01-22 11:48:55,063 INFO org.apache.hadoop.hdfs.server.datanode.DataNode:
STARTUP_MSG: /************************************************************ 
STARTUP_MSG: Starting DataNode STARTUP_MSG: host = cy-ubuntu/127.0.1.1 STARTUP_MSG: 
args = [] STARTUP_MSG: version = 1.2.1
STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.2 -r 1503152; 
compiled by 'mattf' on Mon Jul 22 15:23:09 PDT 2013 STARTUP_MSG: 
java = 1.7.0_25 ************************************************************/ 
2015-01-22 11:48:57,531 INFO org.apache.hadoop.metrics2.impl.MetricsConfig: loaded properties from hadoop-metrics2.properties 
2015-01-22 11:48:57,651 INFO org.apache.