Jenkins Selenium Plugin Failed to Initialize

I have installed the Jenkins Selenium Plugin but on startup it fails to initialize.

Jenkins Startup Logs

> java.net.SocketTimeoutException: Accept timed out 	at
> java.base/java.net.PlainSocketImpl.socketAccept(Native Method) 	at
> java.base/java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:458)
> 	at java.base/java.net.ServerSocket.implAccept(ServerSocket.java:565)
> 	at java.base/java.net.ServerSocket.accept(ServerSocket.java:533) 	at
> hudson.slaves.Channels.newJVM(Channels.java:227) 	at
> hudson.plugins.selenium.process.SeleniumProcessUtils.createSeleniumGridVM(SeleniumProcessUtils.java:59)
> 	at hudson.plugins.selenium.PluginImpl.startHub(PluginImpl.java:176)
> 	at
> hudson.plugins.selenium.PluginImpl.postInitialize(PluginImpl.java:136)
> 	at hudson.PluginManager$2$1$2.run(PluginManager.java:575) 	at
> org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:169)
> 	at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:296) 	at
> jenkins.model.Jenkins$5.runTask(Jenkins.java:1131) 	at
> org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:214) 	at
> org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117) 	at
> jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:59)
> 	at
> java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
> 	at
> java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
> 	at java.base/java.lang.Thread.run(Thread.java:834)

then

> Completed initialization Aug 14, 2020 2:50:17 PM WARNING
> jenkins.model.Jenkins  Exception in onOnline() for the computer
> listener class hudson.plugins.selenium.ComputerListenerImpl on the
> Jenkins master node java.lang.NullPointerException 	at
> hudson.plugins.selenium.PluginImpl.startSeleniumNode(PluginImpl.java:458)
> 	at
> hudson.plugins.selenium.ComputerListenerImpl.onOnline(ComputerListenerImpl.java:30)

It seems to be failing at 'hudson.slaves.Channels.newJVM(Channels.java:227)'

Things I have tried -

• Disabling the firewall
• Reinstalling the plugin
• Setting debug level to ALL to help debug
• Changing Jenkins URL in Jenkins Location

Slave nodes can connect to master with no issues.

• Java - 11.0.8+10-post-Ubuntu-0ubuntu118.04.1
• Jenkins - 2.252
• OS - Linux (ubuntu 18.04) Azure VM
• Selenium Plugin 3.141.59

What could be causing this?

I had a similar issue, I think the main reason is the the plugin is not compatible with java 11. There is also another logfile /var/lib/jenkins/selenium.log where you can see the following output after jenkins was started:

 /usr/lib/jvm/java-11-openjdk-amd64/bin/java -cp /var/cache/jenkins/war/WEB-INF/lib/remoting-4.5.jar hudson.remoting.Launcher -cp /var/lib/jenkins/plugins/selenium/WEB-INF/lib/selenium-server-standalone-3.141.59.jar:/var/lib/jenkins/plugins/selenium/WEB-INF/lib/htmlunit-driver-standalone-2.33.3.jar -connectTo localhost:37677
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by hudson.remoting.Launcher (file:/var/cache/jenkins/war/WEB-INF/lib/remoting-4.5.jar) to method java.net.URLClassLoader.addURL(java.net.URL)
WARNING: Please consider reporting this to the maintainers of hudson.remoting.Launcher
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Exception in thread "main" java.lang.IllegalArgumentException: object is not an instance of declaring class
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at hudson.remoting.Launcher.addClasspath(Launcher.java:154)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at io.jenkins.remoting.shaded.org.kohsuke.args4j.spi.MethodSetter.addValue(MethodSetter.java:47)
	at io.jenkins.remoting.shaded.org.kohsuke.args4j.spi.StringOptionHandler.parseArguments(StringOptionHandler.java:19)
	at io.jenkins.remoting.shaded.org.kohsuke.args4j.CmdLineParser.parseArgument(CmdLineParser.java:520)
	at hudson.remoting.Launcher.main(Launcher.java:293)

If you run jenkins with java 8 the plugin will work.