How do I change Java Runtime Parameters?

Question

On Windows, I could change how much RAM Java could use by typing something like -Xincgc -Xmx2048M in the Java Runtime Parameters. How can I do that in Ubuntu?

Solution 1

If I am not mistaken they are the same in Linux. With the Java command you have the 2 options:

• Xmx sets the maximum memory heap size.
• Xms sets the minimum memory heap size.

So doing -Xmx1024m -Xms128m should work.

Here is an extract from doing a man java in the terminal

-Xmsn
                Specify the initial size, in bytes, of the memory allocation
                pool. This value must be a multiple of 1024 greater than 1MB.
                Append the letter k or K to indicate kilobytes, or m or M to
                indicate megabytes. The default value is chosen at runtime
                based on system configuration. For more information, see
                HotSpot Ergonomics
                Examples:

                       -Xms6291456
                       -Xms6144k
                       -Xms6m

 -Xmxn
                Specify the maximum size, in bytes, of the memory allocation
                pool. This value must a multiple of 1024 greater than 2MB.
                Append the letter k or K to indicate kilobytes, or m or M to
                indicate megabytes. The default value is chosen at runtime
                based on system configuration. For more information, see
                HotSpot Ergonomics
                Examples:

                       -Xmx83886080
                       -Xmx81920k
                       -Xmx80m

So that basically sums it up about doubts using the same parameters.

To use this go to a terminal and type it with a jar program. In my example I am using the minecraft server: java -Xms1024M -Xmx2048M -jar minecraft.jar.

Here is an image of what happens:

I should note that the parameters are Case Sensitive. So xmx1024M is not the same as Xmx1024M.

Solution 2

The same applies on Linux. If you want to make the options permanent, you can export the JAVA_OPTS environment variable.

I recommend to do it on a per-user basis. Modify the .profile file in your home directory (or .bash_profile if it exists and you use bash) to include this line:

export JAVA_OPTS='-Xincgc -Xmx2048M'

After setting this, you need to restart shell sessions for it to apply.

Alternatively, you can also modify the system-wide profile in /etc/profile.

Edit: Settings for the Java Browser Plugin are defined in the Java Control Panel: http://docs.oracle.com/javase/1.4.2/docs/guide/plugin/developer_guide/control_panel.html.

Comments

[Andri]

Well, I didn't ask what parameters I should use. I asked where I should type the parameters. If I type -Xmx1204m -Xms128m, it says unknown command.

[Andri]

How does the same apply to Linux? I can't go to Control Panel, open Java and change the settings. What do I do?

[jjmontes]

If I'm not wrong, that control pannel applies only to the Java Plugin for the Browser. If that is what you look for,it is located at /jre/bin/ControlPanel (docs.oracle.com/javase/1.4.2/docs/guide/plugin/developer_gu‌​ide/…)

[Andri]

That's not what I meant. All I need to know is how I could make Java be able to use more RAM than it does now.