Small Footprint JRE (Linux only)
The Small Footprint JRE, available on Linux® operating systems only, contains a lightweight version of the IBM® runtime environment for Java™.
This lightweight version of the runtime environment is based on the runtime environment within the IBM SDK, Java Technology Edition product for Linux. The lightweight runtime environment is designed for web developers who want to develop and deploy Java applications in the cloud environment. The Small Footprint JRE is available as a Docker image. For more information about the runtime environment and Docker, see IBM SDK, Java Technology Edition and Docker.
Java tools and functions that are not required in the cloud environment, such as the Java control panel, are removed from the lightweight runtime environment. The runtime environment is stripped down to provide core, essential function that has a greatly reduced disk and memory footprint.
The lightweight runtime environment uses compressed references for 64-bit runtime environments. When the virtual machine uses compressed references, all references to objects, classes, threads, and monitors are stored as 32-bit values. The use of compressed references improves the performance of many applications because objects are smaller, resulting in less frequent garbage collection and improved memory cache utilization.
The first line shows the version:
java version "1.8.0" Java(TM) SE Runtime Environment (build pxa6480sr3-20160428_01(SR3) Small Footprint) IBM J9 VM (build 2.8, JRE 1.8.0 Linux amd64-64 Compressed References 20160427_301573 (JIT enabled, AOT enabled) J9VM - R28_Java8_SR3_20160427_1620_B301573 JIT - tr.r14.java.green_20160329_114288 GC - R28_Java8_SR3_20160427_1620_B301573_CMPRSS J9CL - 20160427_301573) JCL - 20160421_01 based on Oracle jdk8u91-b14
java version "1.8.0".
This guide explains which tools and functions are removed from the lightweight runtime environment. If you are using the runtime environment in a cloud and require libraries or classes that are not available, you can customize the runtime environment by packaging extra files in a resources folder.