[Hadoop-common-user] Lock in_use.lock failed when using nfs in namenode

Hi
I want to use nfs to save a copy of the data in namenode, and the nfs
dir /mnt/nfs/dfs/ can be read and written. Things seem to be right, but when
i format the hdfs, "ERROR common.Storage: Cannot create lock on
/mnt/nfs/dfs/name/in_use.lock" occur.
how to solve the problem?

Peng