If you get these errors:

Unexpected error. Unable to verify database connection. 

Checking the logs, we see the following:

2019-06-24 23:42:18,402 INFO scm-web-118667:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/clusters/2/healthStatusBar
2019-06-24 23:42:18,404 INFO scm-web-119745:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/clusters/2/statusContent
2019-06-24 23:42:18,412 INFO scm-web-118667:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/clusters/2/healthStatusBar, Status:200
2019-06-24 23:42:18,420 INFO scm-web-119745:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/clusters/2/statusContent, Status:200
2019-06-24 23:42:19,481 INFO scm-web-119111:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/testConnection
2019-06-24 23:42:19,489 INFO scm-web-119111:com.cloudera.cmf.service.ServiceHandlerRegistry: Executing host command HiveTestDatabaseConnection with sensitive arguments. Host: DbHost{id=28, hostId=a787204f-931d-47e0-8aef-534ab6355a7a, hostName=cm-r01en01.mws.mds.xyz}
2019-06-24 23:42:19,500 INFO scm-web-119111:com.cloudera.cmf.service.ServiceHandlerRegistry: Executing host command OozieTestDatabaseConnection with sensitive arguments. Host: DbHost{id=28, hostId=a787204f-931d-47e0-8aef-534ab6355a7a, hostName=cm-r01en01.mws.mds.xyz}
2019-06-24 23:42:19,506 INFO scm-web-119111:com.cloudera.cmf.service.ServiceHandlerRegistry: Executing host command HueTestDatabaseConnection with sensitive arguments. Host: DbHost{id=28, hostId=a787204f-931d-47e0-8aef-534ab6355a7a, hostName=cm-r01en01.mws.mds.xyz}
2019-06-24 23:42:19,809 INFO scm-web-119111:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/testConnection, Status:200
2019-06-24 23:42:19,826 INFO avro-servlet-hb-processor-1:com.cloudera.server.common.AgentAvroServlet: (45 skipped) AgentAvroServlet: heartbeat processing stats: average=12ms, min=8ms, max=79ms.
2019-06-24 23:42:21,847 INFO scm-web-120167:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult
2019-06-24 23:42:21,854 INFO scm-web-120167:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult, Status:200
2019-06-24 23:42:23,890 INFO scm-web-120477:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult
2019-06-24 23:42:23,896 INFO scm-web-120477:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult, Status:200
2019-06-24 23:42:24,373 WARN avro-servlet-hb-processor-0:com.cloudera.server.cmf.AgentProtocolImpl: Received Process Heartbeat for unknown (or duplicate) process. Ignoring. This is expected to happen once after old process eviction or process deletion (as happens in restarts). id=242 name=null host=a787204f-931d-47e0-8aef-534ab6355a7a/cm-r01en01.mws.mds.xyz
2019-06-24 23:42:24,374 WARN avro-servlet-hb-processor-0:com.cloudera.server.cmf.AgentProtocolImpl: Received Process Heartbeat for unknown (or duplicate) process. Ignoring. This is expected to happen once after old process eviction or process deletion (as happens in restarts). id=243 name=null host=a787204f-931d-47e0-8aef-534ab6355a7a/cm-r01en01.mws.mds.xyz
2019-06-24 23:42:24,374 WARN avro-servlet-hb-processor-0:com.cloudera.server.cmf.AgentProtocolImpl: Received Process Heartbeat for unknown (or duplicate) process. Ignoring. This is expected to happen once after old process eviction or process deletion (as happens in restarts). id=244 name=null host=a787204f-931d-47e0-8aef-534ab6355a7a/cm-r01en01.mws.mds.xyz
2019-06-24 23:42:25,935 INFO scm-web-119807:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult
2019-06-24 23:42:25,942 INFO scm-web-119807:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult, Status:200
2019-06-24 23:42:28,049 INFO scm-web-119778:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult
2019-06-24 23:42:28,056 INFO scm-web-119778:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult, Status:200
2019-06-24 23:42:29,383 INFO scm-web-120247:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/clusters/2/healthStatusBar
2019-06-24 23:42:29,394 INFO scm-web-120247:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/clusters/2/healthStatusBar, Status:200
2019-06-24 23:42:29,395 INFO scm-web-120167:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/clusters/2/statusContent
2019-06-24 23:42:29,422 INFO scm-web-120167:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/clusters/2/statusContent, Status:200
2019-06-24 23:42:30,084 INFO scm-web-118667:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult
2019-06-24 23:42:30,091 INFO scm-web-118667:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult, Status:200
2019-06-24 23:42:32,124 INFO scm-web-120167:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult
2019-06-24 23:42:32,131 INFO scm-web-120167:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult, Status:200
2019-06-24 23:42:33,205 INFO CommandPusher:com.cloudera.cmf.service.AbstractOneOffHostCommand: Unsuccessful 'HueTestDatabaseConnection'
2019-06-24 23:42:33,207 INFO CommandPusher:com.cloudera.cmf.service.AbstractDbConnectionTestCommand: Command exited with code: 1
2019-06-24 23:42:33,207 INFO CommandPusher:com.cloudera.cmf.service.AbstractDbConnectionTestCommand: [24/Jun/2019 23:42:28 +0000] 30846 MainThread redactor     INFO     Started launcher: /opt/cloudera/cm-agent/service/hue/hue.sh is_db_alive
[24/Jun/2019 23:42:28 +0000] 30846 MainThread redactor     ERROR    Redaction rules file doesn't exist, not redacting logs. file: redaction-rules.json, directory: /run/cloudera-scm-agent/process/247-HUE-test-db-connection
[24/Jun/2019 23:42:28 +0000] 30846 MainThread redactor     INFO     Re-exec watcher: /opt/cloudera/cm-agent/bin/cm proc_watcher 30867
+ date
+ date
Mon Jun 24 23:42:30 EDT 2019
++ dirname /opt/cloudera/cm-agent/service/hue/hue.sh
+ cloudera_config=/opt/cloudera/cm-agent/service/hue
++ cd /opt/cloudera/cm-agent/service/hue/../common
++ pwd
+ cloudera_config=/opt/cloudera/cm-agent/service/common
+ . /opt/cloudera/cm-agent/service/common/cloudera-config.sh
++ : /opt/cloudera/cm
++ export CLOUDERA_DIR
++ set -x
+ source_parcel_environment
+ '[‘ ‘!’ -z ” ‘]'
+ locate_cdh_java_home
+ '[‘ -z ” ‘]'
+ '[‘ -z /usr/libexec/bigtop-utils ‘]'
+ local BIGTOP_DETECT_JAVAHOME=
+ for candidate in '"${JSVC_HOME}"' '"${JSVC_HOME}/.."' '"/usr/lib/bigtop-utils"' '"/usr/libexec"'
+ '[‘ -e /usr/libexec/bigtop-utils/bigtop-detect-javahome ‘]'
+ for candidate in '"${JSVC_HOME}"' '"${JSVC_HOME}/.."' '"/usr/lib/bigtop-utils"' '"/usr/libexec"'
+ '[‘ -e /usr/libexec/bigtop-utils/../bigtop-detect-javahome ‘]'
+ for candidate in '"${JSVC_HOME}"' '"${JSVC_HOME}/.."' '"/usr/lib/bigtop-utils"' '"/usr/libexec"'
+ '[‘ -e /usr/lib/bigtop-utils/bigtop-detect-javahome ‘]'
+ for candidate in '"${JSVC_HOME}"' '"${JSVC_HOME}/.."' '"/usr/lib/bigtop-utils"' '"/usr/libexec"'
+ '[‘ -e /usr/libexec/bigtop-detect-javahome ‘]'
+ '[‘ -z ” ‘]'
+ echo 'Cannot find CDH'\''s bigtop-detect-javahome.'
+ exit 1

2019-06-24 23:42:33,207 ERROR CommandPusher:com.cloudera.cmf.model.DbCommand: Command 742(HueTestDatabaseConnection) has completed. finalstate:FINISHED, success:false, msg:Unexpected error. Unable to verify database connection.
2019-06-24 23:42:34,168 INFO scm-web-119807:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult
2019-06-24 23:42:34,175 INFO scm-web-119807:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult, Status:200
2019-06-24 23:42:36,228 INFO scm-web-120167:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult
2019-06-24 23:42:36,234 INFO scm-web-120167:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult, Status:200
2019-06-24 23:42:37,481 INFO CommandPusher:com.cloudera.cmf.service.AbstractOneOffHostCommand: Successful 'OozieTestDatabaseConnection'
2019-06-24 23:42:37,483 INFO CommandPusher:com.cloudera.cmf.service.AbstractDbConnectionTestCommand: Command exited with code: 0
2019-06-24 23:42:37,483 INFO CommandPusher:com.cloudera.cmf.service.AbstractDbConnectionTestCommand: + local MISCJAVA_HOME_CANDIDATES
+ case ${BIGTOP_JAVA_MAJOR} in
+ JAVA_HOME_CANDIDATES=(${JAVA8_HOME_CANDIDATES[@]} ${MISCJAVA_HOME_CANDIDATES[@]} ${OPENJAVA8_HOME_CANDIDATES[@]} ${JAVA11_HOME_CANDIDATES[@]} ${OPENJAVA11_HOME_CANDIDATES[@]})
+ '[‘ -z ” ‘]'
+ for candidate_regex in '${JAVA_HOME_CANDIDATES[@]}'
++ ls -rvd /usr/java/jdk1.8.0_181-cloudera
+ for candidate in '`ls -rvd ${candidate_regex}* 2>/dev/null`'
+ '[‘ -e /usr/java/jdk1.8.0_181-cloudera/bin/java ‘]'
+ export JAVA_HOME=/usr/java/jdk1.8.0_181-cloudera
+ JAVA_HOME=/usr/java/jdk1.8.0_181-cloudera
+ break 2
+ verify_java_home
+ '[‘ -z /usr/java/jdk1.8.0_181-cloudera ‘]'
+ echo JAVA_HOME=/usr/java/jdk1.8.0_181-cloudera
+ source_parcel_environment
+ '[‘ ‘!’ -z ” ‘]'
+ JAVA=/usr/java/jdk1.8.0_181-cloudera/bin/java
+ [[ -z /opt/cloudera/cm ]]
+ MGMT_CLASSPATH='/opt/cloudera/cm/lib/*'
+ JDBC_JARS=/usr/share/java/mysql-connector-java.jar:/opt/cloudera/cm/lib/postgresql-42.1.4.jre7.jar:/usr/share/java/oracle-connector-java.jar
+ MGMT_CLASSPATH='/usr/share/java/mysql-connector-java.jar:/opt/cloudera/cm/lib/postgresql-42.1.4.jre7.jar:/usr/share/java/oracle-connector-java.jar:/opt/cloudera/cm/lib/*'
++ pwd
+ MGMT_CLASSPATH='/run/cloudera-scm-agent/process/246-OOZIE.OOZIE_SERVER-test-db-connection:/usr/share/java/mysql-connector-java.jar:/opt/cloudera/cm/lib/postgresql-42.1.4.jre7.jar:/usr/share/java/oracle-connector-java.jar:/opt/cloudera/cm/lib/*'
+ MGMT_JAVA_OPTS='-Djava.net.preferIPv4Stack=true '
+ exec /usr/java/jdk1.8.0_181-cloudera/bin/java -Djava.net.preferIPv4Stack=true -Djava.security.egd=file:///dev/urandom -cp '/run/cloudera-scm-agent/process/246-OOZIE.OOZIE_SERVER-test-db-connection:/usr/share/java/mysql-connector-java.jar:/opt/cloudera/cm/lib/postgresql-42.1.4.jre7.jar:/usr/share/java/oracle-connector-java.jar:/opt/cloudera/cm/lib/*' com.cloudera.enterprise.dbutil.DbCommandExecutor db.properties

2019-06-24 23:42:37,483 INFO CommandPusher:com.cloudera.cmf.model.DbCommand: Command 741(OozieTestDatabaseConnection) has completed. finalstate:FINISHED, success:true, msg:Successful
2019-06-24 23:42:37,497 INFO CommandPusher:com.cloudera.cmf.service.AbstractOneOffHostCommand: Successful 'HiveTestDatabaseConnection'
2019-06-24 23:42:37,498 INFO CommandPusher:com.cloudera.cmf.service.AbstractDbConnectionTestCommand: Command exited with code: 0
2019-06-24 23:42:37,498 INFO CommandPusher:com.cloudera.cmf.service.AbstractDbConnectionTestCommand: + MISCJAVA_HOME_CANDIDATES=('/Library/Java/Home' '/usr/java/default' '/usr/lib/jvm/default-java' '/usr/lib/jvm/java-openjdk' '/usr/lib/jvm/jre-openjdk')
+ local MISCJAVA_HOME_CANDIDATES
+ case ${BIGTOP_JAVA_MAJOR} in
+ JAVA_HOME_CANDIDATES=(${JAVA8_HOME_CANDIDATES[@]} ${MISCJAVA_HOME_CANDIDATES[@]} ${OPENJAVA8_HOME_CANDIDATES[@]} ${JAVA11_HOME_CANDIDATES[@]} ${OPENJAVA11_HOME_CANDIDATES[@]})
+ '[‘ -z ” ‘]'
+ for candidate_regex in '${JAVA_HOME_CANDIDATES[@]}'
++ ls -rvd /usr/java/jdk1.8.0_181-cloudera
+ for candidate in '`ls -rvd ${candidate_regex}* 2>/dev/null`'
+ '[‘ -e /usr/java/jdk1.8.0_181-cloudera/bin/java ‘]'
+ export JAVA_HOME=/usr/java/jdk1.8.0_181-cloudera
+ JAVA_HOME=/usr/java/jdk1.8.0_181-cloudera
+ break 2
+ verify_java_home
+ '[‘ -z /usr/java/jdk1.8.0_181-cloudera ‘]'
+ echo JAVA_HOME=/usr/java/jdk1.8.0_181-cloudera
+ source_parcel_environment
+ '[‘ ‘!’ -z ” ‘]'
+ JAVA=/usr/java/jdk1.8.0_181-cloudera/bin/java
+ [[ -z /opt/cloudera/cm ]]
+ MGMT_CLASSPATH='/opt/cloudera/cm/lib/*'
+ JDBC_JARS=/usr/share/java/mysql-connector-java.jar:/opt/cloudera/cm/lib/postgresql-42.1.4.jre7.jar:/usr/share/java/oracle-connector-java.jar
+ MGMT_CLASSPATH='/usr/share/java/mysql-connector-java.jar:/opt/cloudera/cm/lib/postgresql-42.1.4.jre7.jar:/usr/share/java/oracle-connector-java.jar:/opt/cloudera/cm/lib/*'
++ pwd
+ MGMT_CLASSPATH='/run/cloudera-scm-agent/process/245-HIVE-test-db-connection:/usr/share/java/mysql-connector-java.jar:/opt/cloudera/cm/lib/postgresql-42.1.4.jre7.jar:/usr/share/java/oracle-connector-java.jar:/opt/cloudera/cm/lib/*'
+ MGMT_JAVA_OPTS='-Djava.net.preferIPv4Stack=true '
+ exec /usr/java/jdk1.8.0_181-cloudera/bin/java -Djava.net.preferIPv4Stack=true -Djava.security.egd=file:///dev/urandom -cp '/run/cloudera-scm-agent/process/245-HIVE-test-db-connection:/usr/share/java/mysql-connector-java.jar:/opt/cloudera/cm/lib/postgresql-42.1.4.jre7.jar:/usr/share/java/oracle-connector-java.jar:/opt/cloudera/cm/lib/*' com.cloudera.enterprise.dbutil.DbCommandExecutor db.properties

2019-06-24 23:42:37,498 INFO CommandPusher:com.cloudera.cmf.model.DbCommand: Command 740(HiveTestDatabaseConnection) has completed. finalstate:FINISHED, success:true, msg:Successful
2019-06-24 23:42:38,336 INFO scm-web-118667:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult
2019-06-24 23:42:38,351 INFO scm-web-118667:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/dbTestConn/checkConnectionResult, Status:200
2019-06-24 23:42:40,393 INFO scm-web-120237:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/clusters/2/healthStatusBar
2019-06-24 23:42:40,418 INFO scm-web-119778:com.cloudera.enterprise.JavaMelodyFacade: Entering HTTP Operation: Method:POST, Path:/clusters/2/statusContent
2019-06-24 23:42:40,421 INFO scm-web-120237:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/clusters/2/healthStatusBar, Status:200
2019-06-24 23:42:40,435 INFO scm-web-119778:com.cloudera.enterprise.JavaMelodyFacade: Exiting HTTP Operation: Method:POST, Path:/clusters/2/statusContent, Status:200
^C
[root@cm-r01nn01 ~]#

Verify you have the right bigtop packages installed:

[root@cm-r01nn01 cloudera-scm-agent]#
[root@cm-r01nn01 cloudera-scm-agent]#
[root@cm-r01nn01 cloudera-scm-agent]# ls -altri /usr/libexec/bigtop-detect-javahome
ls: cannot access /usr/libexec/bigtop-detect-javahome: No such file or directory
[root@cm-r01nn01 cloudera-scm-agent]# find / -iname bigtop-detect-javahome*
[root@cm-r01nn01 cloudera-scm-agent]# ssh cm-r01nn02
Password:
Last login: Tue Jun 25 23:21:59 2019 from cm-r01nn01.mws.mds.xyz
[root@cm-r01nn02 ~]#
[root@cm-r01nn02 ~]#
[root@cm-r01nn02 ~]#
[root@cm-r01nn02 ~]# find / -iname bigtop-detect-javahome*
/usr/bin/bigtop-detect-javahome
/usr/lib/bigtop-utils/bigtop-detect-javahome
[root@cm-r01nn02 ~]# rpm -qf /usr/bin/bigtop-detect-javahome
rpm -qf bigtop-utils-0.7.0+cdh6.2.0-967373.el7.noarch
[root@cm-r01nn02 ~]# rpm -qf /usr/lib/bigtop-utils/bigtop-detect-javahome
bigtop-utils-0.7.0+cdh6.2.0-967373.el7.noarch
[root@cm-r01nn02 ~]#
 

Secondly, ensure that you have set the JAVA_HOME in the Hosts Configuration of CM to point to the correct JDK home variable.  This ansible code can help create the link to the latest copy of the JDK:

[root@awx01 ansible]# cd /ansible && ansible 'cm*' -m shell -a 'ls -altrid /usr/java/jdk1.8.0_181-cloudera/; ln -s /usr/java/jdk1.8.0_181-cloudera/ /usr/java/latest; ls -altrid /usr/java/latest'

Then use /usr/java/latest in the Hosts Configuration (Look for JAVA_HOME and set it).

Thx,
TK