So I am looking at a heap with jmap on a remote box and I want to force garbage collection on it. How do you do this without popping into jvisualvm or jconsole and friends?
I know you shouldn’t be in the practice of forcing garbage collection — you should just figure out why the heap is big/growing.
I also realize the System.GC() doesn’t actually force garbage collection — it just tells the GC that you’d like it to occur.
Having said that is there a way to do this easily? Some command line app I’m missing?
You can do this via the free jmxterm program.
Fire it up like so:
java -jar jmxterm-1.0-alpha-4-uber.jar
From there, you can connect to a host and trigger GC:
$>open host:jmxport #Connection to host:jmxport is opened $>bean java.lang:type=Memory #bean is set to java.lang:type=Memory $>run gc #calling operation gc of mbean java.lang:type=Memory #operation returns: null $>quit #bye
Look at the docs on the jmxterm web site for information about embedding this in bash/perl/ruby/other scripts. I’ve used popen2 in Python or open3 in Perl to do this.
UPDATE: here’s a one-liner using jmxterm:
echo run -b java.lang:type=Memory gc | java -jar jmxterm-1.0-alpha-4-uber.jar -n -l host:port