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<?xml version="1.0" encoding="UTF-8"?>
<!--This work by Eucalyptus Systems is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License. See the accompanying LICENSE file for more information.-->
<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept outputclass="docs one-sidebar sidebar-first" id="understanding_images">
<title>Image Overview</title>
<p>An image defines what will run on a guest instance with your Eucalyptus cloud. Typically, an
image contains one of the Linux distributions like CentOS, Fedora, Ubuntu, Debian or others. It could also contain one of the supported Windows server versions. The format for these is identical.</p>
<p>Normally when we use the term "image" we mean the root file system. Once bundled, uploaded, and
registered with Eucalyptus, such an image is known as a Eucalyptus machine image (EMI).</p>
<p>There are, however, other types of images that support the EMI. They are the kernel (EKI) and
ramdisk (ERI). They contain kernel modules necessary for
proper functioning of the image. Often, one set of these ERIs and EKIs are used by multiple
EMIs. Once loaded into the Eucalyptus cloud, the EKI and ERI are referred to by the image
and you don't have much interaction with them directly. </p>
<note type="tip">When you run an image, you can override the image's associated kernel and ramdisk
if necessary (for example, if you want to try out another kernel. For more information, see <xref
<p>To help get you started, Eucalyptus provides pre-packaged virtual machines that are ready to
run in your cloud. You can get them at the <xref href=""
format="html" scope="external">Eucalyptus Machine Images</xref> page. Each Eucalyptus image from
this site comes bundled with a correspoding EKI and ERI. You can manually download these images
from the web page, or you can use the Eualyptus Image Store commands to list and describe these
images, as well as to install an image in your cloud. For more information see the Eucalyptus
Image Store section in the <xref
scope="external" format="pdf">Command
Line Reference Guide</xref>.</p>
<!--<note type="note">If you are running the Ubuntu Enterprise Cloud (UEC), the images provided above will not work on the UEC when running in System or Static networking modes.</note>-->
<p>If you find that the pre-packaged images don't meet your needs, you can add an image from an
existing, non-registered image, or create your own image.</p>
<p>Once you've selected and downloaded the image(s) you plan to use, read the details in the
following section for directions about how to bundle, upload and register the images with your Eucalyptus cloud.</p>
<p>To view the status of your newly created and registered EKI, ERI, and EMI images, use the
<cmdname>euca-describe-images</cmdname> command. You can also view image status using the
Dashboard's <uicontrol>Images</uicontrol> page.</p>
<p>Once you have added your image to Eucalyptus, see <xref href="../ug/using_instances.dita"/> section
for information about launching and using instances based on the image. </p>
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