jstack: Target process not responding

I am running Ubuntu server edition and I wanted to take a thread dump of Tomcat.

So, I first tried to find out which PID tomcat uses:

$ jps -l
5809 sun.tools.jps.Jps

But it's not there?

So, I used top instead and found out the PID 5730.

Then I called jstack to get the thread dump:

$ sudo jstack -l 5730
5730: Unable to open socket file: target process not responding or HotSpot VM not loaded
The -F option can be used when the target process is not responding

What's going on? :-(

I already tried to export CATALINA_TMPDIR as described in Jstack and Jstat stopped working with upgrade to JDK6u23 but that didn't change anything:

$ export CATALINA_TMPDIR=/tmp
$ sudo /etc/init.d/tomcat6 restart
 * Stopping Tomcat servlet engine tomcat6
   ...done.
 * Starting Tomcat servlet engine tomcat6
   ...done.
$ sudo jstack -l 5934 // new PID after restart
5934: Unable to open socket file: target process not responding or HotSpot VM not loaded
The -F option can be used when the target process is not responding

Update:

I also tried sudo -u tomcat6 jstack -l -F 5730 > threaddumpexceptions2.txt but it only gives me tons of exceptions on the console.

I got it working by doing two things:

1. Changed call to: sudo -u tomcat6 jstack -J-d64 -m pid
2. Replaced OpenJDK with Sun's original sun-6-jdk and sun-6-jre packages

Explanation for part 1: I switched to 64-bit mode, used sudo and run the command as Tomcat user.

Note: Part 2 might not be necessary. For some users it seems like part 1 is enough. In fact, try to add just the sudo command first. It might already do the trick.

I think you need to run jstack as the same user that runs the Tomcat process. Note also that jps only returns processes for the current user. You would get the pid for the Tomcat process by running jps with sudo or as the Tomcat process user.

This bug report may also be useful: https://bugs.launchpad.net/ubuntu/+source/sun-java6/+bug/597098

@Valmar, I find the same topic post here. Unable to get thread dump? Any ideas why my app blocks?

It seems the workaround is sudo -u tomcat6 kill -3 <pid>.