Get Free Memory on Unix System in Java

Max Rohde

02 Jan 2013 — 1 min read

Background

The opsunit framework allows to continuously run a number of JUnit unit tests and do some maintenance/repair work upon any failed test.

The latest addition to the test suite for the Appjangle platform is a simple unit test, which checks the remaining free memory on the server node. If the free memory goes beyond a certain threshold (e.g. 150 mb), some maintenance work is conducted in order to free memory on the node.

Since the server nodes are running a UNIX derivate, the Java unit test therefore needs to be able to determine the currently available system memory.

Problem

How to determine the available free system memory on a UNIX system from a Java program?

Solution

The first starting point is the 'vmstat' application. This application prints out all different kinds of information for the current system. Together with a few other GNU programs, it can be moulded to return the available free memory:

vmstat -s -S M | egrep -ie 'memory|swap' | grep 'free memory'

It is possible to run this shell script from Java. There are multiple ways to achieve this, many of them troublesome and I ALWAYS do it wrong. Therefore I have assembled my hard-learned best practices (and those of others I could find) in the project java-start-process. Using this project, we can determine the free memory for a UNIX system using the following function:



public static int getFreeMemoryUnixInMb() {
 try {

final String expr = Spawn
 .runCommand(
 new String[] { "/bin/bash", "-c",
 "vmstat -s -S M | egrep -ie 'memory|swap' | grep 'free memory'" },
 null);
 // expr sth like " \t \t778 M free memory "

final String[] elems = expr.split(" |\t");
 for (final String elem : elems) {

try {
 return Integer.valueOf(elem);
 } catch (final Throwable t) {

}
 }

throw new RuntimeException(
 "Could not find free memory within: Elements="
 + Arrays.asList(elems) + " Raw Result=[" + expr
 + "]");

} catch (final Throwable t) {
 throw new RuntimeException(t);
 }
}