hadoop install guide: http://www.cc.ntu.edu.tw/chinese/epaper/0036/20160321_3609.html
seen port 50070 that master's datanode has started but slaves' not
Resolved:
Add slaves hostname per line in /usr/local/hadoop/etc/hadoop/slaves
then run /usr/local/hadoop/sbin/start-dfs.sh and /usr/local/hadoop/sbin/start-yarn.sh in master
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