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MapReduce, mail # user - Re: datanode startup before hostname is resovable


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Re: datanode startup before hostname is resovable
Michael Segel 2012-08-08, 15:18

On Aug 8, 2012, at 9:52 AM, Alan Miller <[EMAIL PROTECTED]> wrote:

> Actually (from day to day)  I don’t get a NEW IP address.
>  
Right...

> The OS just can’t resolve the hostname when the DataNode starts up.
> NameNode, JobTracker & TaskTracker services all start successfully as is.
>  
> > Take out the boot up starting of the cluster and start the cluster manually.
> Sorry, but that’s a silly suggestion as it’s worse than what I do now.
>  
> As soon as I login, the first thing I do is sudo hadoop-hdfs-datanode start
> and I’m ready to go.
>  
> I think all we need to do is postpone the datanode startup for a few seconds.
>  
> Alan

Alan,

While you may find the suggestion silly, I think you should realize that its actually something you really want to do when you're running a real cluster.
Case in point. You've got to take a server down due to a hardware problem. You don't want it to join the cluster at start up because the odds are you want to actually run some diagnostics before releasing the server.
Not to mention that there are a lot of IT shops where there are two different teams managing the cluster. One team manages the physical machine and OS, while the other manages the cluster.

Of course you happen to be running a pseudo cluster on a machine that you turn on and off frequently.
I'm running a pseudo cluster on one of my Linux servers that I try not to power cycle unless I have to.  Even on this machine, I don't have a problem.
But then again, i'm running CentOS.

Sorry I couldn't be more helpful...

-Mike
>  
> From: Michel Segel [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, August 08, 2012 12:48 PM
> To: [EMAIL PROTECTED]
> Cc: [EMAIL PROTECTED]
> Subject: Re: datanode startup before hostname is resovable
>  
> So you're running a pseudo cluster...
>  
> Take out the boot up starting of the cluster and start the cluster manually.
> Even w DHCP, you shouldn't always get a new ip address because your lease shouldn't expire that quickly...
>  
> Manually start Hadoop...
>
>
> Sent from a remote device. Please excuse any typos...
>  
> Mike Segel
>
> On Aug 8, 2012, at 2:43 AM, Alan Miller <[EMAIL PROTECTED]> wrote:
>
> Sure but like I said, I’m on DHCP so my IP always changes.
>  
> In my config files I tried using “localhost4” and “127.0.0.1” but in
> both cases it still uses my FQ hostname instead of 127.0.0.1
> E.g.:
>   STARTUP_MSG:   host = myhostname.mycompany.com/10.11.12.13
>   STARTUP_MSG:   args = []
>   STARTUP_MSG:   version = 2.0.0-cdh4.0.1
>  
> From: /etc/hadoop/conf/core-site.xml
>   <property>
>     <name>fs.default.name</name>
>     <value>hdfs://localhost4:8020</value>
>   </property
>  
> From: /etc/hadoop/conf/mapred-site.xml
>   <property>
>     <name>mapred.job.tracker</name>
>     <value>localhost4:8021</value>
>   </property>
>  
> Alan
> From: Chandra Mohan, Ananda Vel Murugan [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, August 08, 2012 9:19 AM
> To: [EMAIL PROTECTED]
> Subject: RE: datanode startup before hostname is resovable
>  
> I had a similar problem under different circumstances. I added the hostname and ip in /etc/hosts file
>  
> From: Alan Miller [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, August 08, 2012 12:32 PM
> To: [EMAIL PROTECTED]
> Subject: datanode startup before hostname is resovable
>  
> For development I run CDH4 on my local machine  but I notice that I have to
> manually start the datanode (sudo service hadoop-hdfs-datanode start)
> after each reboot.
>  
> Looks like the datanode process is getting started before my DHCP address Is resolvable.
> From:  /var/log/hadoop-hdfs/hadoop-hdfs-datanode-myhost.log
>  
>     2012-08-08 08:44:01,171 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: STARTUP_MSG:
>     ….
>     STARTUP_MSG: Starting DataNode
>     STARTUP_MSG:   host = java.net.UnknownHostException: myhostname: myhostname
>     ….
>     2012-08-08 08:44:02,253 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: Exception in secureMain java.net.UnknownHostException: myhostname: myhostname