Unable to open debugger port in IntelliJ IDEA

If you're on windows you can bypass the socket issue completely by switching to shared memory debugging.

I have encountered the same error while using IntelliJ. Since I have started multiple instances of IntelliJ. While starting two instance it started properly. However, when starting another one, it was giving below error.

unable to open debugger port (127.0.0.1:debug-port-number) java.net.socketexception interrupted function call accept failed

There are basically two places you can check your ports related to debugging in IntelliJ

1. JMX port - you can find this is
2. In Startup/Configuration, there is debug option just click this.

What to Check: If IntelliJ is throwing above error, means issue is any of the above listed ports. To verify this open event log (its available in right corner down) and check the exact message. Event log will have message like below

11:19 PM    Error running 'Tomcat-tp': Address localhost:1098 is already in use

11:19 PM    Error running 'Tomcat-tp': Unable to open debugger port (127.0.0.1:51787): java.net.SocketException "Interrupted function call: accept failed"

Solution-1 Check the JMX port of current intelliJ which is not starting with the working one and verify if JMX ports are not duplicated within IntelliJ instance or any of the software which is running in your machine is not using this port.

Solution-2 If JMX is not duplicated then verify your debug port, check in all IntelliJ instance and do the changes.

Surely either JMX or Debug port is having issue just use unique JMX and Debug port and it will work.

Hope this will help someone.

For me, IntelliJ Event Log (right bottom corner) had below logs:

Error running EntitmentTooling-Debug: Cannot run program "/path-to/apache-tomcat-8.5.15/bin/catalina.sh" (in directory "path-to/apache-tomcat-8.5.15/bin"): error=13, Permission denied

Error running EntitmentTooling-Debug: Unable to open debugger port (127.0.0.1:58804): java.net.SocketException "Socket closed"

The command

$ chmod a+x /path-to/apache-tomcat-8.5.15/bin/catalina.sh

to sufficiently change privileges worked for me.

the key to the issue is in debugger port. I was having the same problem, I was killing every process listening on port 8081 (my http port), 1099 (JMX port), tomcat shutdown port, every java.exe, and still nothing.

The thing is this debugger port is different. If you run the application, it will go through the port you have Tomcat configured for, 8080, 8081 or whatever. But if you run it in Debug mode, it goes through a different port.

If you go edit your Tomcat configuration from IntelliJ, the last tab is Startup/Connection. Here go see the configuration for Debug mode, and you'll see its port. Mine was 50473. I changed it to 50472, and everything started working again.