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Hadoop, mail # user - Piping output of hadoop command


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Re: Piping output of hadoop command
Harsh J 2013-02-18, 18:01
Hi,

The command you're looking for is not -copyToLocal (it doesn't really
emit the file, which you seem to need here), but rather a simple -cat:

Something like the below would make your command work:

$ hadoop fs -cat FILE_IN_HDFS | ssh REMOTE_HOST "dd of=TARGET_FILE"

On Mon, Feb 18, 2013 at 10:46 PM, Julian Wissmann
<[EMAIL PROTECTED]> wrote:
> Hi,
>
> we're running a Hadoop cluster with hbase for the purpose of
> evaluating it as database for a research project and we've more or
> less decided to go with it.
> So now I'm exploring backup mechanisms and have decided to experiment
> with hadoops export functionality for that.
>
> What I am trying to achieve is getting data out of hbase and into hdfs
> via hadoop export and then copy it out of hdfs onto a backup system.
> However while copying data out of hdfs to the backup machine I am
> experiencing problems.
>
> What I am trying to do is the following:
>
> hadoop fs -copyToLocal FILE_IN_HDFS | ssh REMOTE_HOST "dd of=TARGET_FILE"
>
> It creates a file on the remote host, however this file is 0kb in
> size; instead of copying any data over there, the file just lands in
> my home folder.
>
> The command output looks like this: hadoop fs -copyToLocal
> FILE_IN_HDFS | ssh REMOTE_HOST "dd of=FILE_ON REMOTE_HOST"
> 0+0 Datensätze ein
> 0+0 Datensätze aus
> 0 Bytes (0 B) kopiert, 1,10011 s, 0,0 kB/s
>
> I cannot think of any reason, why this command would behave in this
> way. Is this some Java-ism that I'm missing here (like not correctly
> treating stdout), or am I actually doing it wrong?
>
> The Hadoop Version is 2.0.0-cdh4.1.2
>
> Regards
>
> Julian

--
Harsh J