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I'm very new to Linux (and haven't done much with cmd line in Windows either), and I'm needing to increase my Java heap size to 3GB from 850MB (total of 4GB of RAM on the box).

I've looked at a couple sites for guidance on increasing my heap size, but none of the commands I've taken from them seem to be working.

For reference I've looked at:

• How do I change Java Runtime Parameters?




• How to increase JAVA Heap Size?




• Find out your Java heap memory size




• JAVA_OPTS for increasing heap size

Based on the information in those questions, I've tried the following commands:

java -Xmx3072m

java -Xmx3g

java JAVA_OPTS="-Xmx3g"

JAVA_OPTS="-Xmx3g"

After each I get no errors (except the third command, that one errors), but when I run `

Via

java -Xmx3072m <your_class_name>

or

java -Xmx3072m -jar <your_jar_file>

or

JAVA_OPTS="-Xmx3G"

java "$JAVA_OPTS" -jar <your_jar_file>

Example

% java -Xmx80m -XshowSettings:all -jar HelloWorld.jar

…                  

VM settings:

    Max. Heap Size: 80.00M

    Ergonomics Machine Class: server

    Using VM: Java HotSpot(TM) 64-Bit Server VM

…

all described in man java

-Xmxsize

    Specifies the maximum size (in bytes) of the memory allocation pool

    in bytes. This value must be a multiple of 1024 and greater than

    2 MB. Append the letter k or K to indicate kilobytes, m or M to

    indicate megabytes, g or G to indicate gigabytes. The default

    value is chosen at runtime based on system configuration. For server

    deployments, -Xms and -Xmx are often set to the same value. See the

    section "Ergonomics" in Java SE HotSpot Virtual Machine Garbage

    Collection Tuning Guide at

    http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/index.html.



    The following examples show how to set the maximum allowed size of

    allocated memory to 80 MB using various units:



    -Xmx83886080

    -Xmx81920k

    -Xmx80m



    The -Xmx option is equivalent to -XX:MaxHeapSize.

• 
  

  java JAVA_OPTS="-Xmx3g"

  
  
  

  Can't work, JAVA_OPTS= … isn't a valid parameter for java

  
  


• 
  

  JAVA_OPTS="-Xmx3g"

  
  
  

  Works, but useless in your case, because you define an environment variable without using it, eg:

  
  
  

  % JAVA_OPTS="-Xmx3g"
  
  % echo $JAVA_OPTS
  
  -Xmx3g