Jmap can't connect to make a dump

Question

We have an open beta of an app which occasionally causes the heapspace to overflow. The JVM reacts by going on a permanent vacation.

To analyze this I would like to

Answer 1

The solution was very simple. I was running the jmap as root, but I had to run it as the user who started the jvm. I will now go hide my head in shame.

Answer 2

Follow the below steps to take the thread and Heap dumps from a docker container

1. Run the below command to bash into the container. Please change the CONTAINER_NAME appropriately

   docker exec -it CONTAINER_NAME bash

2. Then type jps to find the all the Java application details and extract the PID for your application

jps

3. Then run the below command to get the thread dump. Please change the PID appropriately

   jstack PID > threadDump.tdump 
   

4. Then run the below command to get the Heap dump. Please change the PID appropriately

    jmap -dump:live,format=b,file=heapDump.hprof PID 

5. Then exit from the docker container and download the threadDump.tdump and heapDump.hprof from the docker container by running the below command. Please change the CONTAINER_NAME appropriately

 sudo docker cp CONTAINER_NAME:threadDump.tdump .
 sudo docker cp CONTAINER_NAME:heapDump.hprof .