standalone模式启动spark的时候报错：

[hduser@master spark-2.4.0-bin-2.6.0-cdh5.7.0]$ ./sbin/start-all.sh 
starting org.apache.spark.deploy.master.Master, logging to /home/hduser/app/spark-2.4.0-bin-2.6.0-cdh5.7.0/logs/spark-hduser-org.apache.spark.deploy.master.Master-1-master.out
localhost: starting org.apache.spark.deploy.worker.Worker, logging to /home/hduser/app/spark-2.4.0-bin-2.6.0-cdh5.7.0/logs/spark-hduser-org.apache.spark.deploy.worker.Worker-1-master.out
localhost: failed to launch: nice -n 0 /home/hduser/app/spark-2.4.0-bin-2.6.0-cdh5.7.0/bin/spark-class org.apache.spark.deploy.worker.Worker --webui-port 8081 spark://master:7077
localhost:   JAVA_HOME is not set
localhost: full log in /home/hduser/app/spark-2.4.0-bin-2.6.0-cdh5.7.0/logs/spark-hduser-org.apache.spark.deploy.worker.Worker-1-master.out
[hduser@master spark-2.4.0-bin-2.6.0-cdh5.7.0]$ jps
3424 Jps
3303 Master

答：首先确认已经安装好了jdk , 如果安装好了需要配置JAVA_HOME，可以在spark-env.sh中配置，配置时输入如下代码;

export JAVA_HOME=/usr/local/jdk/your_version

这样就可以正常启动spark了