Namenode not getting started

I was facing the issue of namenode not starting. I found a solution using following:

1. first delete all contents from temporary folder: rm -Rf <tmp dir> (my was /usr/local/hadoop/tmp)
2. format the namenode: bin/hadoop namenode -format
3. start all processes again:bin/start-all.sh

You may consider rolling back as well using checkpoint (if you had it enabled).

hadoop.tmp.dir in the core-site.xml is defaulted to /tmp/hadoop-${user.name} which is cleaned after every reboot. Change this to some other directory which doesn't get cleaned on reboot.

Following STEPS worked for me with hadoop 2.2.0,

STEP 1 stop hadoop

hduser@prayagupd$ /usr/local/hadoop-2.2.0/sbin/stop-dfs.sh

STEP 2 remove tmp folder

hduser@prayagupd$ sudo rm -rf /app/hadoop/tmp/

STEP 3 create /app/hadoop/tmp/

hduser@prayagupd$ sudo mkdir -p /app/hadoop/tmp
hduser@prayagupd$ sudo chown hduser:hadoop /app/hadoop/tmp
hduser@prayagupd$ sudo chmod 750 /app/hadoop/tmp

STEP 4 format namenode

hduser@prayagupd$ hdfs namenode -format

STEP 5 start dfs

hduser@prayagupd$ /usr/local/hadoop-2.2.0/sbin/start-dfs.sh

STEP 6 check jps

hduser@prayagupd$ $ jps
11342 Jps
10804 DataNode
11110 SecondaryNameNode
10558 NameNode

In conf/hdfs-site.xml, you should have a property like

<property>
    <name>dfs.name.dir</name>
    <value>/home/user/hadoop/name/data</value>
</property>

The property "dfs.name.dir" allows you to control where Hadoop writes NameNode metadata. And giving it another dir rather than /tmp makes sure the NameNode data isn't being deleted when you reboot.