hadoop dfsadmin是命令行的管理工具，查看帮助用如下命令：
hadoop dfsadmin -help所以dfsadmin是hadoop程序的一个参数，而不是独立的工具。不过现在版本有点变化，hadoop dfsadmin的用法已经被废止，改为hdfs dfsadmin命令。
下面是查看简单的报告：
hduser@namenode:~$ hdfs dfsadmin -report Configured Capacity: 295283847168 (275.00 GB) Present Capacity: 267895083008 (249.50 GB) DFS Remaining: 267894972416 (249.50 GB) DFS Used: 110592 (108 KB) DFS Used%: 0.00% Under replicated blocks: 0 Blocks with corrupt replicas: 0 Missing blocks: 0 ------------------------------------------------- Datanodes available: 3 (3 total, 0 dead) Live datanodes: Name: 192.168.1.73:50010 (datanode1) Hostname: datanode1 Decommission Status : Normal Configured Capacity: 98427949056 (91.67 GB) DFS Used: 36864 (36 KB) Non DFS Used: 9129578496 (8.50 GB) DFS Remaining: 89298333696 (83.17 GB) DFS Used%: 0.00% DFS Remaining%: 90.72% Configured Cache Capacity: 0 (0 B) Cache Used: 0 (0 B) Cache Remaining: 0 (0 B) Cache Used%: 100.00% Cache Remaining%: 0.00% Last contact: Mon Mar 10 03:09:14 UTC 2014 Name: 192.168.1.75:50010 (datanode3) Hostname: datanode3 Decommission Status : Normal Configured Capacity: 98427949056 (91.67 GB) DFS Used: 36864 (36 KB) Non DFS Used: 9129590784 (8.50 GB) DFS Remaining: 89298321408 (83.17 GB) DFS Used%: 0.00% DFS Remaining%: 90.72% Configured Cache Capacity: 0 (0 B) Cache Used: 0 (0 B) Cache Remaining: 0 (0 B) Cache Used%: 100.00% Cache Remaining%: 0.00% Last contact: Mon Mar 10 03:09:16 UTC 2014 Name: 192.168.1.74:50010 (datanode2) Hostname: datanode2 Decommission Status : Normal Configured Capacity: 98427949056 (91.67 GB) DFS Used: 36864 (36 KB) Non DFS Used: 9129594880 (8.50 GB) DFS Remaining: 89298317312 (83.17 GB) DFS Used%: 0.00% DFS Remaining%: 90.72% Configured Cache Capacity: 0 (0 B) Cache Used: 0 (0 B) Cache Remaining: 0 (0 B) Cache Used%: 100.00% Cache Remaining%: 0.00% Last contact: Mon Mar 10 03:09:14 UTC 2014
hduser@namenode:~$ hdfs dfsadmin -printTopology Rack: /default-rack 192.168.1.73:50010 (datanode1) 192.168.1.74:50010 (datanode2) 192.168.1.75:50010 (datanode3)
rack指的是机架，目前三台datanode虚拟机位于一个物理主机上，所以都是default-rack。以后应该要演化成多个rack上的配置。可以用一个物理机模拟一个rack。
详细参考官方文档：http://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/CommandsManual.html#dfsadmin
下面这个命令参数很有用，可以在HDFS集群运行时增加新的datanode后，让namenode重新读取配置文件里面的hosts列表。
| -refreshNodes | Re-read the hosts and exclude files to update the set of Datanodes that are allowed to connect to the Namenode and those that should be decommissioned or recommissioned. |
Ubuntu上使用Hadoop 2.x 八 HDFS cluster管理命令,布布扣,bubuko.com
Ubuntu上使用Hadoop 2.x 八 HDFS cluster管理命令
原文：http://blog.csdn.net/csfreebird/article/details/20906441