It is possible to bind and connect to localhost:8080 at the same time - application server will probably compete with some other software on the port

Hello,

There is a check performed for the free port. The following 2 conditions which happen at the same time lead to this message:

• it's possible to connect to localhost:8080 while Tomcat is not started yet (usually it means that there is something listening on this port, but it could be also an antivirus)
• it's possible to bind to 127.0.0.1:8080 port despite something is probably running on it already, some systems allow several apps to bind to the same address/port.

One of the users reported this:

Thanks for the information. After a bit of digging, I found the root cause. In my case, on Mac OS X, I have Cisco's AnyConnect VPN installed (for work). AnyConnect "hijacks" common HTTP ports (80, 8080) and a simple connect to the port will succeed, even though there is not an application bound to it. I'm not sure how they do this exactly, but thought you would like to know in case other people have the same issue. I'll just start using port 8090 for tomcat instead, to avoid the message.

Note that IDEA doesn't block you from running the server, it just reports that the normal ports check has discovered the situation where IDEA can't know for sure whether the server may have problems starting up.
The presence of this warning allows us to better handle the support situation when there INDEED is conflict between ports.

Regards,
Michael

It was indeed caused by an antivirus software. I've done some configuration tweaks and the problem is gone. Thanks!