[wplug] [wplug-announce] The Open Pitt, Issue 18
Vance Kochenderfer
vkochend at nyx.net
Thu Dec 1 20:00:30 EST 2005
PDF version: <http://www.wplug.org/top/wplug-top018.pdf>
THE OPEN PITT
What's cooking in Linux and Open Source in Western Pennsylvania
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Issue 18 November 2005 www.wplug.org
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In this issue:
Building an Embedded Gentoo System
October Roundup
Announcement: New WPLUG Officers Chosen
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Coming Events
Dec. 3: General User Meeting, Topic: Mandriva. 10am to 2pm, 1507 Newell-
Simon Hall, CMU
Dec. 17: Tutorial, Topic: Intro to Objective C. 10am to 3pm, 1507 Newell-
Simon Hall, CMU
Jan. 7: Installfest. 10am to 5pm, 1507 Newell-Simon Hall, CMU
Jan. 14: General User Meeting. 10am to 2pm, 1507 Newell-Simon Hall, CMU
The public is welcome at all events
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Building an Embedded Gentoo System
by Tom Watson
Why would you want to build your own embedded Gentoo system? Firstly, it's
not quite as hard as you might think. You may have an old PC with limited
resources that you'd like to turn into a web server or NFS server. Or you
may have a more traditional embedded system like those found at
<http://www.soekris.com/> that you would like to get running.
To follow along with this article you won't need any special hardware. It
can all be built and tested on your desktop Linux box. Some helpful files
can be found at the URL
<http://www.shadysidesupercomputingcenter.com/sywt/gentoo.embedded/>, such
as a step-by-step script named "sywt.ge.stepbystep.txt."
The first thing to do is log in as root and create a working directory; I
used /opt/embedded. Next we need to download a stage1 tarball and a
portage snapshot. These can be found on the Gentoo mirrors (the step-by-
step script includes URLs).
The stage1 tarball provides us with a base set of tools we need to build
our embedded system. The portage snapshot provides us with the latest
package dependency database and tools.
Once these files are downloaded we need to create our arch directory, which
is where we will do the real work. Since my target is an i386 machine we
do as follows:
# mkdir i386
# cd i386
Now that we have a working directory we need to unpack our stage1 tarball
(working tools) and the portage snapshot:
# tar -jxf ../stage1*
# tar -jxf ../portage* -C usr
The "-C usr" means change to the usr directory before extracting the files,
which puts the portage files in the correct location. Next we need to give
our build environment access to the special files in /proc by mounting our
proc directory onto the work file system:
# mount --bind /proc proc
We also need to copy a valid resolv.conf file to the working filesystem so
Internet addresses can be looked up for the upcoming install:
# cp /etc/resolv.conf etc/resolv.conf
Now we can enter our new environment and start working in our newly-
created little Linux box. I generally use the "nice" command to give a
lower priority to subsequent operations. This helps prevent the build
process from slowing down other activities on the machine:
# /bin/nice -n 19 chroot . /bin/bash --login
# env-update
# source /etc/profile
Now our shell is running inside the new environment and anything we do only
affects the embedded system. If needed, customize the etc/make.conf file
to set compiler options, match your target environment, and include any
desired USE flags. For this article we will just stick with the defaults
and build for the i386 architecture, so we can skip this step.
At this point we also need to change our build profile to suit the embedded
target. We will be using uClibc, a special version of libc designed for
microcontrollers and other small systems. Switching is just a matter of
softlinking the uClibc profile to /etc/make.profile:
# unlink /etc/make.profile
# ln -sf /usr/portage/profiles/uclibc/x86/2005.1/ /etc/make.profile
Now we are ready to bootstrap the system. This procedure builds our
development environment:
# cd /usr/portage/scripts
# ./bootstrap.sh
You can step away from your machine for a while now as it builds. Once
complete, we can then rebuild our base system to match our make flags and
the rest of the build environment:
# emerge -e system
You can step away again for a while now...
OK, now we have a pretty much fully-fledged Gentoo base system. The next
thing is to create our rootfs, the directory where we put the files that
will end up in actual image. We also need to install a base layout into
the directory structure, and emerge the required tools for the system.
You will see "ROOT=/rootfs" in front of most of these commands. This tells
emerge to install the results in /rootfs:
# mkdir /rootfs
# cd /usr/portage/sys-apps/baselayout-lite/
# ROOT=/rootfs emerge baselayout-lite-1.0_pre1.ebuild
# ROOT=/rootfs emerge uclibc
# ROOT=/rootfs emerge busybox
BusyBox is a really neat piece of software. It replaces the standard
binutils packages with a single file and a whole lot of symlinks to this
file. Based on the command used to run it, BusyBox modifies its behavior.
If invoked as "ls" it gives a directory listing, as "cp" it copies files,
and so on for many of the standard UNIX commands. This greatly reduces the
size of the system which is exactly what we want.
Now that BusyBox is installed, we need to create the symlinks:
# mount -o bind /proc/ /rootfs/proc/
# chroot /rootfs /bin/busybox --install -s
# umount /rootfs/proc
Next we should probably set the root password on the box:
# chroot /rootfs /bin/ash
# passwd
# rm /etc/passwd-
# exit
We also need to download, configure, and build a kernel. There is a
kernel.config file on the web site configured for this article. It's
easier to build the kernel outside of the chroot environment. If you don't
want to compile your own, a prebuilt 2.6.14.2 kernel is available on the
web site. Copy your kernel to /rootfs/boot.
The last thing to do before we build an image is to edit our
/rootfs/etc/fstab file to include the root filesystem. Add a line
containing "/dev/hda / reiserfs defaults" to this file.
The /rootfs directory now contains your complete system. For this article,
we will use the QEMU emulator to run our little system instead of booting
it directly.
Create a tarball of all the files to go into the QEMU image:
# cd /rootfs
# rm -R /rootfs/var/lib/portage/
# rm -R /rootfs/var/db/pkg/*
# cd /rootfs
# tar -zcf ../rootfs.tgz .
# exit
The last exit command will take you out of the chroot environment and back
to the regular shell.
If QEMU is not already installed on your machine, you'll have to do that
now. Then you create an empty 64 megabyte image file and format it with
the Reiser filesystem:
# qemu-img create gentoo.img 64M
# mkfs.reiserfs -q gentoo.img
To put your embedded filesystem onto the empty image file, mount it using
the loopback device. Here we're mounting it on /mnt/floppy (use a
different mount point on your system if you wish):
# mount -o loop gentoo.img /mnt/floppy
Then you'll untar the root filesystem into the image and unmount it:
# tar -zxf rootfs.tgz -C /mnt/floppy
# umount /mnt/floppy
Finally, boot the image with QEMU:
# qemu -hda gentoo.img -kernel rootfs/boot/kernel-2.6.14.2 -append
"root=/dev/hda"
Congratulations, you now have a basic running system. There is still a lot
of configuration (such as networking) that needs to be done, but I'll leave
that up to you.
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October Roundup
Oct. 15 General User Meeting: Patrick Wagstrom spoke about the interactions
between weblogs and Open Source. He covered some of the popular weblog
packages and described various methods used to aggregate or link together
weblogs. Patrick demonstrated how this information can be used to study
whether, and to what extent, different Open Source projects interact.
Oct. 22 Tutorials: Bill Moran covered the Simple Object Access Protocol
(SOAP), which is increasingly being used for distributed applications.
After reviewing the basics, he described some of the programming libraries
that can provide your applications with SOAP functionality. Mike O'Connor
followed with a discussion of how and under what conditions Linux can be
successfully used within a small organization. As an example, he used
First Trinity Evangelical Lutheran Church, which has a mixed Linux,
Windows, and Macintosh environment.
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Announcement: New WPLUG Officers Chosen
Five members of the Board of Directors were elected by the WPLUG membership
at the November 5 Annual Meeting. They have taken the following offices:
Chair: Bill Moran
Vice-Chair: Beth Lynn Eicher
Secretary: David Ostroske
Treasurer: Patrick Wagstrom
Director-at-Large: Chris Teodorski
Thanks go to them and to all the candidates who stepped forward to run in
WPLUG's first election.
Of course, WPLUG will still need plenty of other volunteers to keep its
events going. You should post to the <wplug-plan at wplug.org> mailing list
if you have an interest in helping out.
===========================================================================
The Open Pitt is published by the Western Pennsylvania Linux Users Group
<http://www.wplug.org/top/>
Editors: Elwin Green, Vance Kochenderfer
Copyright 2005 Western Pennsylvania Linux Users Group. Any article in
this newsletter may be reprinted elsewhere in any medium, provided it is
not changed and attribution is given to the author and WPLUG.
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