CDH登录后显示【无法发出查询：Host Monitor 未运行】解决办法

现象：CDH登录后显示【无法发出查询：Host Monitor 未运行】

出现问题后，首先检查日志：

/var/log/cloudera-scm-server/cloudera-scm-server.log

2018-06-01 11:58:00,001 INFO 618348787@agentServer-2579:com.cloudera.server.common.MonitoringThreadPool: agentServer: waiting in queue stats: average=0ms, min=0ms, max=1ms.
2018-06-01 11:58:24,208 INFO ScmActive-0:com.cloudera.server.cmf.components.ScmActive: (119 skipped) ScmActive completed successfully.
2018-06-01 11:58:38,291 ERROR DatabaseSizeGauge-0:com.cloudera.enterprise.DatabaseSizeGauge: Failed to execute db size query.
java.lang.NullPointerException
        at com.cloudera.enterprise.dbutil.DbUtil.getDatabaseSize(DbUtil.java:736)
        at com.cloudera.enterprise.DatabaseSizeGauge.run(DatabaseSizeGauge.java:75)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)
2018-06-01 11:58:59,293 INFO CMMetricsForwarder-0:com.cloudera.server.cmf.components.ClouderaManagerMetricsForwarder: Failed to send metrics.
java.lang.ArrayIndexOutOfBoundsException: 0

如果显示上述错误，查看根目录df -h

查看根目录是否爆满，如果爆满则清理根目录下的一些日志信息，腾出空间来。

然后，搜索Service Monitor