How do I set Java's min and max heap size through environment variables?

Question

I know that the heap sizes can be set when launching java, but I would like to have this adjusted through environment variables on my server.

The accepted answer is out of date and does not apply anymore. Refer to @Gauthier's answer if you end up here — Layman
– Layman, Commented Aug 12, 2020 at 16:30

nickb · Accepted Answer · 2013-11-12 20:33:38Z

100

You can't do it using environment variables directly. You need to use the set of "non standard" options that are passed to the java command. Run: java -X for details. The options you're looking for are -Xmx and -Xms (this is "initial" heap size, so probably what you're looking for.)

Some products like Ant or Tomcat might come with a batch script that looks for the JAVA_OPTS environment variable, but it's not part of the Java runtime. If you are using one of those products, you may be able to set the variable like:

set JAVA_OPTS="-Xms128m -Xmx256m"

You can also take this approach with your own command line like:

set JAVA_OPTS="-Xms128m -Xmx256m"  
java ${JAVA_OPTS} MyClass

edited Nov 12, 2013 at 20:33

nickb

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answered Jan 6, 2009 at 16:32

Todd

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2 Comments

Mutant Bob Over a year ago

The JAVA_OPTS technique is also used by the scripts generated by the maven appassemble plugin.

keisar Over a year ago

as @neves mentioned in a comment below this has changed in java 7 (docs.oracle.com/javase/7/docs/webnotes/tsg/TSG-VM/html/…). you can use JAVA_TOOL_OPTIONS (see link and answers below)

wmli · Accepted Answer · 2013-07-12 11:11:03Z

80

If you want any java process, not just ant or Tomcat, to pick up options like -Xmx use the environment variable _JAVA_OPTIONS.

In bash: export _JAVA_OPTIONS="-Xmx1g"

answered Jul 12, 2013 at 11:11

wmli

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2 Comments

tim_hutton Over a year ago

In Windows: set _JAVA_OPTIONS=-Xmx1g To make it permanent, make a new environment variable _JAVA_OPTIONS and set it to -Xmx1g

Vadzim Over a year ago

See also Difference between _JAVA_OPTIONS and JAVA_TOOL_OPTIONS

gotson · Accepted Answer · 2019-11-08 02:31:53Z

46

You can use JAVA_TOOL_OPTIONS.

Example:

export JAVA_TOOL_OPTIONS=-Xmx512m

It has been mentioned in some comments, and in another answer.

The OP's question is quite old, but as it is the first google result for the question, I thought i would add the answer here for clarity's sake.

answered Nov 8, 2019 at 2:31

gotson

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1 Comment

GG. Over a year ago

Should be the new accepted answer.

Community · Accepted Answer · 2017-05-23 12:34:38Z

18

Actually, there is a way to set global defaults for Sun's JVM via environment variables.

See How to set a java system property so that it is effective whenever I start JVM without adding it to the command line arguments.

edited May 23, 2017 at 12:34

CommunityBot

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answered Oct 4, 2012 at 8:18

Vadzim

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Comments

a2800276 · Accepted Answer · 2009-01-06 16:21:49Z

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You can't do it using environment variables. It's done via "non standard" options. Run: java -X for details. The options you're looking for are -Xmx and -Xms (this is "initial" heap size, so probably what you're looking for.)

answered Jan 6, 2009 at 16:21

a2800276

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1 Comment

neves Over a year ago

It looks it changed in Java 7: docs.oracle.com/javase/7/docs/webnotes/tsg/TSG-VM/html/…

frankodwyer · Accepted Answer · 2009-01-06 16:26:52Z

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I think your only option is to wrap java in a script that substitutes the environment variables into the command line

answered Jan 6, 2009 at 16:26

frankodwyer

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Comments

Christopher Schultz · Accepted Answer · 2010-02-18 15:55:28Z

A couple of notes:

Apache ant doesn't know anything about JAVA_OPTS, while Tomcat's startup scripts do. For Apache ant, use ANT_OPTS to affect the environment for the JVM that runs /ant/, but not for the things that ant might launch.
The maximum heap size you can set depends entirely on the environment: for most 32-bit systems, the maximum amount of heap space you can request, regardless of available memory, is in the 2GiB range. The largest heap on a 64-bit system is "really big". Also, you are practically limited by physical memory as well, since the heap is managed by the JVM and you don't want a lot of swapping going on to the disk.
For server environments, you typically want to set -Xms and -Xmx to the same value: this will fix the size of the heap at a certain size and the garbage collector has less work to do because the heap will never have to be re-sized.

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