You try to start Hadoop's dfs in a multi-node deployment. All the Hadoop nodes are running Linux. You run this:
You see this:
Starting namenodes on [hadoopmaster]
hadoopmaster: starting namenode, logging to /usr/local/hadoop/logs/hadoop-root-namenode-hadoopmaster.out
root@hadoopdatanode's password: localhost: starting datanode, logging to /usr/local/hadoop/logs/hadoop-root-datanode-hadoopmaster.out
hadoopmaster: starting datanode, logging to /usr/local/hadoop/logs/hadoop-root-datanode-hadoopmaster.out
localhost: ulimit -a for user root
localhost: core file size (blocks, -c) 0
localhost: data seg size (kbytes, -d) unlimited
localhost: scheduling priority (-e) 0
localhost: file size (blocks, -f) unlimited
localhost: pending signals (-i) 2544
localhost: max locked memory (kbytes, -l) 64
localhost: max memory size (kbytes, -m) unlimited
localhost: open files (-n) 1024
localhost: pipe size (512 bytes, -p) 8
You notice that DFS is not running properly on the datanode (aka slave node). You think the prompts for "root@hadoopdatanode" (the Hadoop slave server) are a sign of the problem. What do you do?
If you want to passwordlessly SSH as a given user from one server to another, the remote server's authorized_keys must have the public key from the local server (server from which you attempt to initiate the SSH connection).
In this case you are being prompted for a password. The remote server would not do this if its /root/.ssh/authorized_keys had the id_rsa.pub file for the root user on the starting (local) server. The starting server is the Hadoop master server.
From the Hadoop namenode (aka master) server, do this:
Copy the output to the last line of /root/.ssh/authorized_keys on the destination (non-master) Hadoop datanode server.