Can't launch jstat : Could not reserve enough space for object heap

I have an old Jboss server, with 5go of RAM. My java app is configured like that :

...-server -Xms3200m -Xmx3500m -XX:MaxPermSize=512M...


When I try to shutdown, it uses the same JAVA_OPTS as the start, so it fail. So I modify the shutdown.sh script, and add :

...
JAVA_OPTS='-Xms128m -Xmx128m -XX:MaxPermSize=128m'
export JAVA_OPTS
...


Everything works fine. But now, it's my JMX stats which don't work anymore, I assume they uses jstat to mesure the free heap.

When I do a :

./jstat -gccapacity PID


I have the message :

Could not reserve enough space for object heap


But I have 1go of RAM free on the server at this time ! What JAVA_OPTS jstat use work ?

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