Where would namenode and datanode be installed if not defined in hdfs-site.xml?
In hdfs-default.xml dfs.datanode.data.dir default value is file://${hadoop.tmp.dir}/dfs/data and dfs.namenode.name.dir file://${hadoop.tmp.dir}/dfs/name
And in core-default.xml hadoop.tmp.dir value is /tmp/hadoop-${user.name}
Hence datanode located in /tmp/hadoop-${user.name}/dfs/data and namenode will be at /tmp/hadoop-${user.name}/dfs/name location.