Where are default JVM heap sizes defined on linux (SL4)

Question

I'm currently using sun's java 1.6 on a SL4 cluster.

For some reason, the 1.6 JVM is starting up with an impossibly large heap, and cannot start:

java -version
Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.

If I start it with e.g. -Xmx1800M, then it works OK. So, I'm wondering where the default heap size is set, and more importantly how to change it?

The machine has 8GB of physical memory, and I believe that sun's server JVM is supposed to start with a default of half the memory up to 512M, but this is clearly not the case, as it's trying to allocate over 1800M.

EDIT: I realise that it's possible to use _JAVA_OPTIONS, but this feels a bit clunky; I was expecting a properties file somewhere, but so far I've been unable to find it.

Answer 1

There is no properties file for this. According to Garbage Collector Ergonomics:

initial heap size:

Larger of 1/64th of the machine's physical memory on the machine or some reasonable minimum. Before J2SE 5.0, the default initial heap size was a reasonable minimum, which varies by platform. You can override this default using the -Xms command-line option.

maximum heap size:

Smaller of 1/4th of the physical memory or 1GB. Before J2SE 5.0, the default maximum heap size was 64MB. You can override this default using the -Xmx command-line option.

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Note: The boundaries and fractions given for the heap size are correct for J2SE 5.0. They are likely to be different in subsequent releases as computers get more powerful.

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Given you have 8GB of RAM, default maximum heap size should be 1GB assuming you're using Java 6.

Answer 2

There's no standard properties file. The (Sun) JVM has the default values hardcoded in it.