Thread dump in Jetty

Normally if you have a problem with dead-locked threads or you want to know what is taking so long in a running application you can get the JVM to do a thread dump for you by sending the QUIT signal like this:

First get the process id using

ps | grep java

then send the quit signal

kill -QUIT <your-pid>

But this was not working for me on my server running Jetty 6.1 as installed by the .deb installation. The logs showed nothing.

After a bit of searching on the interweb I found the new (to me) method of generating stack traces using

sudo jstack <pid>

This was slightly more helpful and told me:

"Unable to open socket file: target process not responding or HotSpot VM not loaded"

At last I had something to go on and found that jstack must be run as the same user as the java process - which in the case of Jetty as installed by the debian install files is "jetty"

sudo -u jetty jstack <your-pid>

worked a treat and so did

sudo -u jetty kill -QUIT <your-pid>