启动问题：
执行start-all.sh出现以下异常信息：
failed to launch: nice -n 0 /bin/spark-class org.apache.spark.deploy.worker.Worker --webui-port 8081 spark://master:7077
解决方案：
Just added export JAVA_HOME=/usr/java/default in /root/.bashrc
su root vi /root/.bashrc export JAVA_HOME=/opt/jdk1.8.0_171
之后尝试重新启动hadoop。
参考《https://blog.csdn.net/Abandon_Sun/article/details/76686398》
《https://stackoverflow.com/questions/33955635/why-does-start-all-sh-from-root-cause-failed-to-launch-org-apache-spark-deploy》