How to capture a Java thread dump using jstack

When troubleshooting various problems on the Content Gateway one might need to capture a Java thread dump. This KB article explains how to do that using jstack.

Prerequisites

jstack needs to be installed, and may not be installed by default. To check whether jstack is installed or not please run the following command:

If jstack is installed, progress to the "Instructions" section below. If not please install the OpenJDK development package according to the current version of Cloud Gateway.

Check your existing CloudGateway server level:

If you are currently running Gateway version 7.10.7 or earlier, then please install using:

if you are currently running Gateway version 8.0 or later, then please install using:

Instructions

1. Collect out the PID of the Content Gateway process by running this command

   PID=$(ps aux | grep [c]loudgateway.pid | awk '{ print $2 }')

2. Capture the thread dump using jstack and the open file descriptors using lsof by running these commands using the PID determined at step 1

   jstack $PID > thread_dump.txt lsof -p $PID > lsof.txt

3. If the above command does not capture anything, try running this to force a thread dump from a non-responsive process:

   jstack -F $PID > thread_dump.txt

4. If you are using JDK 11+, forcing a thread dump requires this command

   jhsdb jstack --locks --pid $PID > thread_dump.txt

5. Repeat the jstack/lsof commands 3 times total a few seconds apart like this:

   for i in $(seq 3); do jstack $PID > thread_dump-$i.txt; lsof -p $PID > lsof-$i.txt; sleep 60;done

   or ( for JDK 8 )

   for i in $(seq 3); do jstack -F $PID > thread_dump-$i.txt; lsof -p $PID > lsof-$i.txt; sleep 60;done

or (for JDK11+)

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