[SOLVED] 0 Active Nodes when running Hadoop and Yarn in pseudo-distributed mode on CentOS 7

Issue

Symptoms:

• sbin/start-dfs.sh and sbin/start-yarn.sh execute without errors, but localhost:8088 shows 0 active nodes.
• mapreduce jobs fail to connect to ResourceManager at /0.0.0.0:8032
• Password-less (public key) ssh is enabled and working.
• core-site.xml, hdfs-site.xml, mapred-site.xml, and yarn-site.xml are all configured correctly.
• OS is CentOS 7 running on Oracle VirtualBox.

Solution

Solution:

• Not stated in the tutorial I was following: CentOS needs to be configured to allow a connection to the local machine.
• I edited the file /etc/hosts with root permissions.
• I added a line containing my machine's numeric ip address, a space, and then the machine's host name (as configured during the CentOS installation).
• (In my virtual configuration, this was the ip address of the virtual machine's "host-only adapter".)
• I stopped, and then restarted, dfs and yarn.
• I checked localhost:8088: 1 active node.
• My mapreduce jobs now executed successfully.

Answered By - Leo Orientis