我正在尝试在集群中运行 2 个 tomcat 服务器，我已在每个服务器的 server.xml 中进行了必要的更改，但在启动服务器时出现以下错误，这可能是什么问题？？
Jun 18, 2013 12:57:55 PM org.apache.catalina.core.AprLifecycleListener init
INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: /usr/lib/jvm/java-6-openjdk-i386/jre/lib/i386/client:/usr/lib/jvm/java-6-openjdk-i386/jre/lib/i386:/usr/lib/jvm/java-6-openjdk-i386/jre/../lib/i386:/usr/java/packages/lib/i386:/usr/lib/i386-linux-gnu/jni:/lib/i386-linux-gnu:/usr/lib/i386-linux-gnu:/usr/lib/jni:/lib:/usr/lib
Jun 18, 2013 12:57:56 PM org.apache.tomcat.util.digester.Digester endElement
WARNING: No rules found matching 'Server/Service/Engine/Membership'.
Jun 18, 2013 12:57:56 PM org.apache.tomcat.util.digester.Digester endElement
WARNING: No rules found matching 'Server/Service/Engine/Receiver'.
Jun 18, 2013 12:57:56 PM org.apache.tomcat.util.digester.Digester endElement
WARNING: No rules found matching 'Server/Service/Engine/Sender'.
Jun 18, 2013 12:57:56 PM org.apache.tomcat.util.digester.Digester endElement
WARNING: No rules found matching 'Server/Service/Engine/Deployer'.
Jun 18, 2013 12:57:56 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-bio-8009"]
Jun 18, 2013 12:57:56 PM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 807 ms
Jun 18, 2013 12:57:56 PM org.apache.catalina.core.StandardService startInternal
INFO: Starting service Catalina
Jun 18, 2013 12:57:56 PM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.41
Jun 18, 2013 12:57:56 PM org.apache.catalina.cluster.tcp.SimpleTcpCluster start
INFO: Cluster is about to start
Jun 18, 2013 12:57:56 PM org.apache.catalina.cluster.tcp.SimpleTcpCluster start
SEVERE: Unable to start cluster.
java.lang.NullPointerException
at org.apache.catalina.cluster.tcp.SimpleTcpCluster.start(SimpleTcpCluster.java:410)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1106)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:302)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:443)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:732)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.startup.Catalina.start(Catalina.java:684)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:322)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:456)
Jun 18, 2013 12:57:56 PM org.apache.catalina.startup.Catalina start
SEVERE: Catalina.start:
org.apache.catalina.LifecycleException: Failed to start component [StandardServer[8005]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
at org.apache.catalina.startup.Catalina.start(Catalina.java:684)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:322)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:456)
Caused by: org.apache.catalina.LifecycleException: Failed to start component
[StandardService[Catalina]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:732)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 7 more
Caused by: org.apache.catalina.LifecycleException: Failed to start component
[StandardEngine[Catalina]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
at
org.apache.catalina.core.StandardService.startInternal(StandardService.java:443)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 9 more
Caused by: org.apache.catalina.LifecycleException: java.lang.NullPointerException
at org.apache.catalina.cluster.tcp.SimpleTcpCluster.start(SimpleTcpCluster.java:434)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1106)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:302)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 11 more
Caused by: java.lang.NullPointerException
at org.apache.catalina.cluster.tcp.SimpleTcpCluster.start(SimpleTcpCluster.java:410)
... 14 more
Jun 18, 2013 12:57:56 PM org.apache.catalina.startup.Catalina start
INFO: Server startup in 151 ms