how to setup selenium webdriver in eclipse linux

i try this code (web driver every thing and update java also) i try this code in windows its working fine but linux cant plz help me to how can i fix this error?

import java.util.concurrent.TimeUnit;

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;


public class openfire {


    public static void main(String[] args) {
        WebDriver driver = new FirefoxDriver();
        driver.manage().window().maximize();
        driver.manage().timeouts().implicitlyWait(25, TimeUnit.SECONDS);
        driver.get("http://ift.tt/2eKtpiF");
    }

}

the out put is

Exception in thread "main" java.lang.IllegalStateException: The path to the driver executable must be set by the webdriver.gecko.driver system property; for more information, see http://ift.tt/26SIDUn. The latest version can be downloaded from http://ift.tt/1UjgqPJ
    at com.google.common.base.Preconditions.checkState(Preconditions.java:738)
    at org.openqa.selenium.remote.service.DriverService.findExecutable(DriverService.java:124)
    at org.openqa.selenium.firefox.GeckoDriverService.access$100(GeckoDriverService.java:41)
    at org.openqa.selenium.firefox.GeckoDriverService$Builder.findDefaultExecutable(GeckoDriverService.java:115)
    at org.openqa.selenium.remote.service.DriverService$Builder.build(DriverService.java:330)
    at org.openqa.selenium.firefox.FirefoxDriver.toExecutor(FirefoxDriver.java:207)
    at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:108)
    at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:104)
    at openfire.main(openfire.java:11)

how can i fix this error?