Databases Reference
In-Depth Information
<!-- Put site-specific property overrides in this file. -->
<configuration>
<property>
<name>dfs.replication</name>
<value>1</value>
<description>The actual number of replications can be specified when the
file is created.</description>
</property>
</configuration>
In
core-site.xml
and
mapred-site.xml
we specify the hostname and port of the
NameNode and the JobTracker, respectively. In
hdfs-site.xml
we specify the default
replication factor for HDFS, which should only be one because we're running on only
one node. We must also specify the location of the Secondary NameNode in the mas-
ters file and the slave nodes in the slaves file:
[hadoop-user@master]$ cat masters
localhost
[hadoop-user@master]$ cat slaves
localhost
While all the daemons are running on the same machine, they still communicate
with each other using the same SSH protocol as if they were distributed over a cluster.
Section 2.2 has a more detailed discussion of setting up the SSH channels, but for
single-node operation simply check to see if your machine already allows you to
ssh
back to itself.
[hadoop-user@master]$ ssh localhost
If it does, then you're good. Otherwise setting up takes two lines.
[hadoop-user@master]$ ssh-keygen -t dsa -P '' -f ~/.ssh/id_dsa
[hadoop-user@master]$ cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys
You are almost ready to start Hadoop. But first you'll need to format your HDFS by
using the command
[hadoop-user@master]$ bin/hadoop namenode -format
We can now launch the daemons by use of the
start-all.sh
script. The Java
jps
command will list all daemons to verify the setup was successful.
[hadoop-user@master]$ bin/start-all.sh
[hadoop-user@master]$ jps
26893 Jps
26832 TaskTracker
26620 SecondaryNameNode
26333 NameNode
26484 DataNode
26703 JobTracker
