Grinberg: /* Overview */

2015-10-21T11:05:25Z

‎Overview

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= Overview =
Android boot image ({{filename|boot.img}} file) packs
* boot header containing, among others, kernel command line
* kernel binary image
* ramdisk serving as the root of Android file system
* optionally, a 2-nd stage bootloader

The boot image format is not limited to Android only - it can pack any OS kernel including, but not limited to, Linux, whereas ramdisk is optional.

Two tools are available for boot image manipulation:
* {{filename|mkbootimg}} - an official utility used to pack boot images. It is a part of Android project.
* {{filename|abootimg}} - an alternative utility used to both pack and unpack boot images.

= Getting mkbootimg =
{{filename|mkbootimg}} is a part of Android project, and is built within Android build process.<br/>
Upon build completion, {{filename|mkbootimg}} binary file is located at {{filename|out/host/linux-x86/bin/mkbootimg}}.

= Getting abootimg =
{{filename|abootimg}} can be obtained in either source code form or via Linux distribution repositories. For example, on Ubuntu platform, {{filename|abootimg}} may be obtained via '''abootimg''' package.

= Sample boot image manipulations =
== Unpacking boot image ==
<pre>
$ abootimg -x boot.img

$ ls
bootimg.cfg # boot header
zImage # kernel
initrd.img # ramdisk
</pre>

== Unpacking ramdisk ==
<pre>
$ mkdir ramdisk
$ cd ramdisk
$ gunzip -c ../initrd.img | cpio -i

$ ls
data
dev
proc
...
</pre>

== Packing ramdisk ==
<pre>
$ cd ramdisk
$ find . | cpio -o -H newc | gzip > ../newramdisk.img
</pre>

== Packing boot image ==
<pre>
$ abootimg --create boot.img -k zImage -r newramdisk.img -c "pagesize=2048" -c "kerneladdr=0x80208000" -c "ramdiskaddr=0x82200000" -c "tagsaddr=0x80200100" -c "cmdline=console=ttyHSL0,115200n8 ..."
</pre>

== Packing boot image with no ramdisk ==
Due to its Android-oriented assumptions, {{filename | abootimg}} does not allow creating ramdisk-less boot image. However, ramdisk-less boot image is quite appropriate for booting Linux. This is possible falling back to mkbootimg utility:
<pre>
$ mkbootimg --kernel zImage --ramdisk NONE --pagesize 2048 --base 0x80200100 --cmdline "console=ttyHSL0,115200n8 ..." --output boot.img
</pre>

= See also =
* [http://android-dls.com/wiki/index.php?title=HOWTO:_Unpack%2C_Edit%2C_and_Re-Pack_Boot_Images Packing and unpacking boot image]
* [http://manpages.ubuntu.com/manpages/natty/man1/abootimg.1.html abootimg man page]

[[Category:Android]]

Android: Boot image - Revision history

Grinberg: /* Overview */