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From Bhooshan Mogal <bhooshan.mo...@gmail.com>
Subject Re: conf.get("dfs.data.dir") return null when hdfs-site.xml doesn't set it explicitly
Date Mon, 08 Sep 2014 21:40:03 GMT
Hi Demai,

When you read a property from the conf object, it will only have a value if
the conf object contains that property.

In your case, you created the conf object as new Configuration() -- adds
core-default and core-site.xml.

Then you added site.xmls (hdfs-site.xml and core-site.xml) from specific
locations. If none of these files have defined dfs.data.dir, then you will
get NULL. This is expected behavior.

What do you mean by retrieving the info from a live cluster? Even for
processes like datanode, namenode etc, the source of truth for these
properties is hdfs-site.xml. It is loaded from a specific location when you
start these services.

Question: Where are you running the above code? Is it on a node which has
other hadoop daemons as well?

My guess is that the path you are referring to (/etc/hadoop/conf.
cloudera.hdfs/core-site.xml) is not the right path where these config
properties are defined. Since this is a CDH cluster, you would probably be
best served by asking on the CDH mailing list as to where the right path to
these files is.


On Mon, Sep 8, 2014 at 11:47 AM, Demai Ni <nidmgg@gmail.com> wrote:

> hi, experts,
> I am trying to get the local filesystem directory of data node. My cluster
> is using CDH5.x (hadoop 2.3) and the default configuration. So the datanode
> is under file:///dfs/dn. I didn't specify the value in hdfs-site.xml.
> My code is something like:
> conf = new Configuration()
> // test both with and without the following two lines
> conf.addResource (new
> Path("/etc/hadoop/conf.cloudera.hdfs/hdfs-site.xml"));
> conf.addResource (new
> Path("/etc/hadoop/conf.cloudera.hdfs/core-site.xml"));
> // I also tried get("dfs.datanode.data.dir"), which also return NULL
> String dnDir = conf.get("dfs.data.dir");  // return NULL
> It looks like the get only look at the configuration file instead of
> retrieving the info from the live cluster?
> Many thanks for your help in advance.
> Demai


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