Hadoop study notes - dfsadmin tool

1  Reports basic filesystem information and statistics
# hadoop dfsadmin -report
Configured Capacity: 20711452672 (19.29 GB)
Present Capacity: 6368899072 (5.93 GB)
DFS Remaining: 3413004288 (3.18 GB)
DFS Used: 2955894784 (2.75 GB)
DFS Used%: 46.41%
Under replicated blocks: 187
Blocks with corrupt replicas: 0
Missing blocks: 0

-------------------------------------------------
Datanodes available: 1 (1 total, 0 dead)

Name: 10.42.197.92:50010
Decommission Status : Normal
Configured Capacity: 20711452672 (19.29 GB)
DFS Used: 2955894784 (2.75 GB)
Non DFS Used: 14342553600 (13.36 GB)
DFS Remaining: 3413004288(3.18 GB)
DFS Used%: 14.27%
DFS Remaining%: 16.48%
Last contact: Tue Feb 28 20:58:50 EST 2012

2 Entering and leaving safe mode

To see whether the namenode is in safe mode, you can use the dfsadmin command:
% hadoop dfsadmin -safemode get
Safe mode is ON

Sometimes you want to wait for the namenode to exit safe mode before carrying out a
command, particularly in scripts. The wait option achieves this:
hadoop dfsadmin -safemode wait
# command to read or write a file

To enter safe mode,use the following command:
% hadoop dfsadmin -safemode enter
Safe mode is ON

You can make the namenode leave safe mode by using:
% hadoop dfsadmin -safemode leave
Safe mode is OFF