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1<html>
2<head>
3<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
4<title>2.8.5.5. Image Generation</title>
5<link rel="stylesheet" type="text/css" href="../book.css">
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8<link rel="up" href="bitbake-dev-environment.html" title="2.8.5. BitBake">
9<link rel="prev" href="package-splitting-dev-environment.html" title="2.8.5.4. Package Splitting">
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11</head>
12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="section" title="2.8.5.5. Image Generation">
13<div class="titlepage"><div><div><h4 class="title">
14<a name="image-generation-dev-environment"></a>2.8.5.5. Image Generation</h4></div></div></div>
15<p>
16 Once packages are split and stored in the Package Feeds area,
17 the OpenEmbedded build system uses BitBake to generate the
18 root filesystem image:
19 </p>
20<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>
21<p>
22 </p>
23<p>
24 The image generation process consists of several stages and
25 depends on several tasks and variables.
26 The
27 <a class="link" href="../ref-manual/ref-tasks-rootfs.html" target="_self"><code class="filename">do_rootfs</code></a>
28 task creates the root filesystem (file and directory structure)
29 for an image.
30 This task uses several key variables to help create the list
31 of packages to actually install:
32 </p>
33<div class="itemizedlist"><ul class="itemizedlist" type="disc">
34<li class="listitem"><p><a class="link" href="../ref-manual/var-IMAGE_INSTALL.html" target="_self"><code class="filename">IMAGE_INSTALL</code></a>:
35 Lists out the base set of packages to install from
36 the Package Feeds area.</p></li>
37<li class="listitem"><p><a class="link" href="../ref-manual/var-PACKAGE_EXCLUDE.html" target="_self"><code class="filename">PACKAGE_EXCLUDE</code></a>:
38 Specifies packages that should not be installed.
39 </p></li>
40<li class="listitem"><p><a class="link" href="../ref-manual/var-IMAGE_FEATURES.html" target="_self"><code class="filename">IMAGE_FEATURES</code></a>:
41 Specifies features to include in the image.
42 Most of these features map to additional packages for
43 installation.</p></li>
44<li class="listitem"><p><a class="link" href="../ref-manual/var-PACKAGE_CLASSES.html" target="_self"><code class="filename">PACKAGE_CLASSES</code></a>:
45 Specifies the package backend to use and consequently
46 helps determine where to locate packages within the
47 Package Feeds area.</p></li>
48<li class="listitem"><p><a class="link" href="../ref-manual/var-IMAGE_LINGUAS.html" target="_self"><code class="filename">IMAGE_LINGUAS</code></a>:
49 Determines the language(s) for which additional
50 language support packages are installed.
51 </p></li>
52<li class="listitem"><p><a class="link" href="../ref-manual/var-PACKAGE_INSTALL.html" target="_self"><code class="filename">PACKAGE_INSTALL</code></a>:
53 The final list of packages passed to the package manager
54 for installation into the image.
55 </p></li>
56</ul></div>
57<p>
58 </p>
59<p>
60 With
61 <a class="link" href="../ref-manual/var-IMAGE_ROOTFS.html" target="_self"><code class="filename">IMAGE_ROOTFS</code></a>
62 pointing to the location of the filesystem under construction and
63 the <code class="filename">PACKAGE_INSTALL</code> variable providing the
64 final list of packages to install, the root file system is
65 created.
66 </p>
67<p>
68 Package installation is under control of the package manager
69 (e.g. dnf/rpm, opkg, or apt/dpkg) regardless of whether or
70 not package management is enabled for the target.
71 At the end of the process, if package management is not
72 enabled for the target, the package manager's data files
73 are deleted from the root filesystem.
74 As part of the final stage of package installation, postinstall
75 scripts that are part of the packages are run.
76 Any scripts that fail to run
77 on the build host are run on the target when the target system
78 is first booted.
79 If you are using a
80 <a class="link" href="../dev-manual/creating-a-read-only-root-filesystem.html" target="_self">read-only root filesystem</a>,
81 all the post installation scripts must succeed during the
82 package installation phase since the root filesystem is
83 read-only.
84 </p>
85<p>
86 The final stages of the <code class="filename">do_rootfs</code> task
87 handle post processing.
88 Post processing includes creation of a manifest file and
89 optimizations.
90 </p>
91<p>
92 The manifest file (<code class="filename">.manifest</code>) resides
93 in the same directory as the root filesystem image.
94 This file lists out, line-by-line, the installed packages.
95 The manifest file is useful for the
96 <a class="link" href="../ref-manual/ref-classes-testimage*.html" target="_self"><code class="filename">testimage</code></a>
97 class, for example, to determine whether or not to run
98 specific tests.
99 See the
100 <a class="link" href="../ref-manual/var-IMAGE_MANIFEST.html" target="_self"><code class="filename">IMAGE_MANIFEST</code></a>
101 variable for additional information.
102 </p>
103<p>
104 Optimizing processes run across the image include
105 <code class="filename">mklibs</code>, <code class="filename">prelink</code>,
106 and any other post-processing commands as defined by the
107 <a class="link" href="../ref-manual/var-ROOTFS_POSTPROCESS_COMMAND.html" target="_self"><code class="filename">ROOTFS_POSTPROCESS_COMMAND</code></a>
108 variable.
109 The <code class="filename">mklibs</code> process optimizes the size
110 of the libraries, while the
111 <code class="filename">prelink</code> process optimizes the dynamic
112 linking of shared libraries to reduce start up time of
113 executables.
114 </p>
115<p>
116 After the root filesystem is built, processing begins on
117 the image through the
118 <a class="link" href="../ref-manual/ref-tasks-image.html" target="_self"><code class="filename">do_image</code></a>
119 task.
120 The build system runs any pre-processing commands as defined
121 by the
122 <a class="link" href="../ref-manual/var-IMAGE_PREPROCESS_COMMAND.html" target="_self"><code class="filename">IMAGE_PREPROCESS_COMMAND</code></a>
123 variable.
124 This variable specifies a list of functions to call before
125 the OpenEmbedded build system creates the final image output
126 files.
127 </p>
128<p>
129 The OpenEmbedded build system dynamically creates
130 <code class="filename">do_image_*</code> tasks as needed, based
131 on the image types specified in the
132 <a class="link" href="../ref-manual/var-IMAGE_FSTYPES.html" target="_self"><code class="filename">IMAGE_FSTYPES</code></a>
133 variable.
134 The process turns everything into an image file or a set of
135 image files and compresses the root filesystem image to reduce
136 the overall size of the image.
137 The formats used for the root filesystem depend on the
138 <code class="filename">IMAGE_FSTYPES</code> variable.
139 </p>
140<p>
141 As an example, a dynamically created task when creating a
142 particular image <em class="replaceable"><code>type</code></em> would take the
143 following form:
144 </p>
145<pre class="literallayout">
146 do_image_<em class="replaceable"><code>type</code></em>[depends]
147 </pre>
148<p>
149 So, if the <em class="replaceable"><code>type</code></em> as specified by the
150 <code class="filename">IMAGE_FSTYPES</code> were
151 <code class="filename">ext4</code>, the dynamically generated task
152 would be as follows:
153 </p>
154<pre class="literallayout">
155 do_image_ext4[depends]
156 </pre>
157<p>
158 </p>
159<p>
160 The final task involved in image creation is the
161 <a class="link" href="../ref-manual/ref-tasks-image-complete.html" target="_self"><code class="filename">do_image_complete</code></a>
162 task.
163 This task completes the image by applying any image
164 post processing as defined through the
165 <a class="link" href="../ref-manual/var-IMAGE_POSTPROCESS_COMMAND.html" target="_self"><code class="filename">IMAGE_POSTPROCESS_COMMAND</code></a>
166 variable.
167 The variable specifies a list of functions to call once the
168 OpenEmbedded build system has created the final image output
169 files.
170 </p>
171<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
172<h3 class="title">Note</h3>
173 The entire image generation process is run under Pseudo.
174 Running under Pseudo ensures that the files in the root
175 filesystem have correct ownership.
176 </div>
177</div></body>
178</html>
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