https://wiki.apache.org/hadoop/FAQ#Does_Hadoop_require_SSH.3F
Hadoop provided scripts (e.g., start-mapred.sh and start-dfs.sh) use ssh in order to start and stop the various daemons and some other utilities. The Hadoop framework in itself does not require ssh. Daemons (e.g. TaskTracker and DataNode) can also be started manually on each node without the script's help.