提交Spark任務時，報錯：
scala> sc.textFile("hdfs://master.hadoop:9000/spark/a.txt").flatMap(_.split(" ")).map((_,1)).reduceByKey(_+_).sortBy(_._2).collect
[Stage 0:> (0 + 0) / 2]
18/08/24 20:44:35 WARN TaskSchedulerImpl: Initial job has not accepted any resources; check your cluster UI to ensure that workers are registered and have sufficient resources
18/08/24 20:44:50 WARN TaskSchedulerImpl: Initial job has not accepted any resources; check your cluster UI to ensure that workers are registered and have sufficient resources
18/08/24 20:45:05 WARN TaskSchedulerImpl: Initial job has not accepted any resources; check your cluster UI to ensure that workers are registered and have sufficient resources
[Stage 0:> (0 + 0) / 2]
18/08/24 20:45:20 WARN TaskSchedulerImpl: Initial job has not accepted any resources; check your cluster UI to ensure that workers are registered and have sufficient resources
18/08/24 20:45:35 WARN TaskSchedulerImpl: Initial job has not accepted any resources; check your cluster UI to ensure that workers are registered and have sufficient resources
18/08/24 20:45:50 WARN TaskSchedulerImpl: Initial job has not accepted any resources; check your cluster UI to ensure that workers are registered and have sufficient resources
正常啓動應用的話，worker機器上應該有這樣的進程（CoarseGrainedExecutorBackend）
[root@slave4 conf]# jps
3472 DataNode
3540 SecondaryNameNode
3798 Worker
3862 CoarseGrainedExecutorBackend
3958 Jps
而如果worker機器上沒有出現的話，說明啓動失敗。
解決辦法：
首先查看spark配置文件是否有配置SPARK_EXECUTOR_MEMORY這個屬性（我的機器是配置的512M）,如果不配置的話默認爲1G，根據自己的情況而定。
export JAVA_HOME=/apps/jdk1.8.0_171
export SCALA_HOME=/apps/scala-2.11.7
export HADOOP_HOME=/apps/hadoop-2.8.0/
export HADOOP_CONF_DIR=/apps/hadoop-2.8.0/etc/hadoop
export SPARK_MASTER_IP=master.hadoop
export SPARK_WORKER_MEMORY=512m
export SPARK_WORKER_CORES=2
export SPARK_WORKER_INSTANCES=1
export SPARK_EXECUTOR_MEMORY=512m
我的機器出現問題就是因爲沒有配置SPARK_EXECUTOR_EMEORY
我以爲只需要配置了SPARK_WORKER_MEMORY就可以了，所以一直出錯。好幾天才搞定！
配置好以後使用top命令查看一下worker結點的空餘內存（free）是否夠用，我的還剩餘765m，所以配置512m是合理的。
[root@slave4 hdptmp]# top
top - 21:59:25 up 3:37, 1 user, load average: 0.24, 0.12, 0.08
Tasks: 111 total, 1 running, 110 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.1 us, 0.1 sy, 0.0 ni, 99.8 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 1867048 total, 765924 free, 630728 used, 470396 buff/cache
KiB Swap: 1048572 total, 1048572 free, 0 used. 1030032 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3472 root 20 0 2830276 154668 19032 S 1.0 8.3 0:20.83 java
再次啓動發現worker節點上啓動了（CoarseGrainedExecutorBackend）進程，並且執行spark程序也成功了。
18/08/30 14:12:40 WARN metastore.ObjectStore: Failed to get database global_temp, returning NoSuchObjectException
Spark context Web UI available at http://192.168.1.5:4040
Spark context available as 'sc' (master = spark://slave3.hadoop:7077, app id = app-20180830141225-0000).
Spark session available as 'spark'.
Welcome to
____ __
/ __/__ ___ _____/ /__
_\ \/ _ \/ _ `/ __/ '_/
/___/ .__/\_,_/_/ /_/\_\ version 2.1.1
/_/
Using Scala version 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_171)
Type in expressions to have them evaluated.
Type :help for more information.
scala> sc
res0: org.apache.spark.SparkContext = org.apache.spark.SparkContext@18356951
scala> sc.textFile("hdfs://slave3.hadoop:9000/a.txt").flatMap(_.split(" ")).map((_, 1)).reduceByKey(_+_).sortBy(_._2).collect
res1: Array[(String, Int)] = Array((jim,1), (jarry,1), (wo,1), (ni,1), (hello,4))
scala>