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Creation involved removing the overview-manual and replacing it with the getting-started manual. All links to the string "&YOCTO_DOCS_OVERVIEW_URL" had to be replaced with "&YOCTO_DOCS_GS_URL" across the entire YP manual set. I renamed files used to create the manual with prefixes suited for the new manual name, which is "Getting Started With Yocto Project". The style sheet for the new manual needed updating to display the new .PNG image for the title page. The mega-manual file had to be updated to include the files. The mega-manual.sed file had to be updated to include the new manual and not use the overview manual. (From yocto-docs rev: 6c7abf9192390121000f577d6c98f259d290d15d) Signed-off-by: Scott Rifenbark <srifenbark@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
179 lines
10 KiB
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179 lines
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>2.8.5.5. Image Generation</title>
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<link rel="stylesheet" type="text/css" href="../book.css">
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<meta name="generator" content="DocBook XSL Stylesheets V1.76.1">
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<link rel="home" href="index.html" title="Getting Started With Yocto Project">
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<link rel="up" href="bitbake-dev-environment.html" title="2.8.5. BitBake">
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<link rel="prev" href="package-splitting-dev-environment.html" title="2.8.5.4. Package Splitting">
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<link rel="next" href="sdk-generation-dev-environment.html" title="2.8.5.6. SDK Generation">
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</head>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="section" title="2.8.5.5. Image Generation">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="image-generation-dev-environment"></a>2.8.5.5. Image Generation</h4></div></div></div>
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<p>
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Once packages are split and stored in the Package Feeds area,
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the OpenEmbedded build system uses BitBake to generate the
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root filesystem image:
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</p>
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<table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 630px"><td align="center"><img src="figures/image-generation.png" align="middle" width="540"></td></tr></table>
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<p>
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</p>
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<p>
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The image generation process consists of several stages and
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depends on several tasks and variables.
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The
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<a class="link" href="../ref-manual/ref-tasks-rootfs.html" target="_self"><code class="filename">do_rootfs</code></a>
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task creates the root filesystem (file and directory structure)
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for an image.
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This task uses several key variables to help create the list
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of packages to actually install:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem"><p><a class="link" href="../ref-manual/var-IMAGE_INSTALL.html" target="_self"><code class="filename">IMAGE_INSTALL</code></a>:
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Lists out the base set of packages to install from
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the Package Feeds area.</p></li>
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<li class="listitem"><p><a class="link" href="../ref-manual/var-PACKAGE_EXCLUDE.html" target="_self"><code class="filename">PACKAGE_EXCLUDE</code></a>:
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Specifies packages that should not be installed.
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</p></li>
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<li class="listitem"><p><a class="link" href="../ref-manual/var-IMAGE_FEATURES.html" target="_self"><code class="filename">IMAGE_FEATURES</code></a>:
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Specifies features to include in the image.
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Most of these features map to additional packages for
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installation.</p></li>
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<li class="listitem"><p><a class="link" href="../ref-manual/var-PACKAGE_CLASSES.html" target="_self"><code class="filename">PACKAGE_CLASSES</code></a>:
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Specifies the package backend to use and consequently
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helps determine where to locate packages within the
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Package Feeds area.</p></li>
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<li class="listitem"><p><a class="link" href="../ref-manual/var-IMAGE_LINGUAS.html" target="_self"><code class="filename">IMAGE_LINGUAS</code></a>:
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Determines the language(s) for which additional
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language support packages are installed.
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</p></li>
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<li class="listitem"><p><a class="link" href="../ref-manual/var-PACKAGE_INSTALL.html" target="_self"><code class="filename">PACKAGE_INSTALL</code></a>:
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The final list of packages passed to the package manager
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for installation into the image.
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</p></li>
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</ul></div>
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<p>
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</p>
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<p>
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With
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<a class="link" href="../ref-manual/var-IMAGE_ROOTFS.html" target="_self"><code class="filename">IMAGE_ROOTFS</code></a>
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pointing to the location of the filesystem under construction and
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the <code class="filename">PACKAGE_INSTALL</code> variable providing the
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final list of packages to install, the root file system is
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created.
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</p>
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<p>
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Package installation is under control of the package manager
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(e.g. dnf/rpm, opkg, or apt/dpkg) regardless of whether or
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not package management is enabled for the target.
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At the end of the process, if package management is not
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enabled for the target, the package manager's data files
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are deleted from the root filesystem.
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As part of the final stage of package installation, postinstall
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scripts that are part of the packages are run.
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Any scripts that fail to run
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on the build host are run on the target when the target system
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is first booted.
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If you are using a
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<a class="link" href="../dev-manual/creating-a-read-only-root-filesystem.html" target="_self">read-only root filesystem</a>,
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all the post installation scripts must succeed during the
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package installation phase since the root filesystem is
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read-only.
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</p>
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<p>
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The final stages of the <code class="filename">do_rootfs</code> task
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handle post processing.
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Post processing includes creation of a manifest file and
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optimizations.
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</p>
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<p>
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The manifest file (<code class="filename">.manifest</code>) resides
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in the same directory as the root filesystem image.
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This file lists out, line-by-line, the installed packages.
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The manifest file is useful for the
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<a class="link" href="../ref-manual/ref-classes-testimage*.html" target="_self"><code class="filename">testimage</code></a>
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class, for example, to determine whether or not to run
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specific tests.
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See the
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<a class="link" href="../ref-manual/var-IMAGE_MANIFEST.html" target="_self"><code class="filename">IMAGE_MANIFEST</code></a>
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variable for additional information.
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</p>
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<p>
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Optimizing processes run across the image include
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<code class="filename">mklibs</code>, <code class="filename">prelink</code>,
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and any other post-processing commands as defined by the
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<a class="link" href="../ref-manual/var-ROOTFS_POSTPROCESS_COMMAND.html" target="_self"><code class="filename">ROOTFS_POSTPROCESS_COMMAND</code></a>
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variable.
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The <code class="filename">mklibs</code> process optimizes the size
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of the libraries, while the
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<code class="filename">prelink</code> process optimizes the dynamic
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linking of shared libraries to reduce start up time of
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executables.
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</p>
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<p>
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After the root filesystem is built, processing begins on
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the image through the
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<a class="link" href="../ref-manual/ref-tasks-image.html" target="_self"><code class="filename">do_image</code></a>
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task.
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The build system runs any pre-processing commands as defined
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by the
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<a class="link" href="../ref-manual/var-IMAGE_PREPROCESS_COMMAND.html" target="_self"><code class="filename">IMAGE_PREPROCESS_COMMAND</code></a>
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variable.
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This variable specifies a list of functions to call before
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the OpenEmbedded build system creates the final image output
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files.
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</p>
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<p>
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The OpenEmbedded build system dynamically creates
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<code class="filename">do_image_*</code> tasks as needed, based
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on the image types specified in the
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<a class="link" href="../ref-manual/var-IMAGE_FSTYPES.html" target="_self"><code class="filename">IMAGE_FSTYPES</code></a>
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variable.
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The process turns everything into an image file or a set of
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image files and compresses the root filesystem image to reduce
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the overall size of the image.
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The formats used for the root filesystem depend on the
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<code class="filename">IMAGE_FSTYPES</code> variable.
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</p>
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<p>
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As an example, a dynamically created task when creating a
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particular image <em class="replaceable"><code>type</code></em> would take the
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following form:
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</p>
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<pre class="literallayout">
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do_image_<em class="replaceable"><code>type</code></em>[depends]
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</pre>
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<p>
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So, if the <em class="replaceable"><code>type</code></em> as specified by the
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<code class="filename">IMAGE_FSTYPES</code> were
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<code class="filename">ext4</code>, the dynamically generated task
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would be as follows:
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</p>
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<pre class="literallayout">
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do_image_ext4[depends]
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</pre>
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<p>
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</p>
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<p>
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The final task involved in image creation is the
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<a class="link" href="../ref-manual/ref-tasks-image-complete.html" target="_self"><code class="filename">do_image_complete</code></a>
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task.
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This task completes the image by applying any image
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post processing as defined through the
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<a class="link" href="../ref-manual/var-IMAGE_POSTPROCESS_COMMAND.html" target="_self"><code class="filename">IMAGE_POSTPROCESS_COMMAND</code></a>
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variable.
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The variable specifies a list of functions to call once the
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OpenEmbedded build system has created the final image output
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files.
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</p>
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<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
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<h3 class="title">Note</h3>
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The entire image generation process is run under Pseudo.
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Running under Pseudo ensures that the files in the root
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filesystem have correct ownership.
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</div>
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</div></body>
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</html>
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