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Pocket Linux Guide
David Horton
<dhorton<AT>NOSPAM.member.fsf.org>
Revision History
Revision 3.1 2005-04-09 Revised by: DH
Minor clarifications and spelling corrections.
Revision 3.0 2004-11-02 Revised by: DH
Changed bootloader to GRUB rather than LILO. Updated versions on all source
code packages. Made minor clarifications to some shell commands and scripts.
Revision 2.1 2004-02-18 Revised by: DH
Corrected typos. Changed resource site hosting to SourceForge. Added appendix
B to include the GNU Free Documentation License as part of this document.
Revision 2.0 2003-11-08 Revised by: DH
Updated to use GNU coreutils in place of fileutils, sh-utils and textutils.
Updated version numbers on many source code packages. Introduced Freshmeat as
a resource for finding source code. Changed /etc/mtab to a real file rather
than using a symlink to /proc/mounts. Corrected local_fs script errors.
Updated email address.
Revision 1.2 2003-05-31 Revised by: DH
Corrected errors in "strip -o library" commands.
Revision 1.1 2003-05-21 Revised by: DH
Bug fixes, typo corrections and improved XML markup.
Revision 1.0 2003-02-17 Revised by: DH
Initial Release, reviewed by LDP.
The Pocket Linux Guide is for anyone interested in learning the techniques of
building a GNU/Linux system from source code. The guide is structured as a
project that builds a small diskette-based GNU/Linux system called Pocket
Linux. Each chapter explores a small piece of the overall system explaining
how it works, why it is needed and how to build it. After completing the
Pocket Linux project, readers should possess an enhanced knowledge of what
makes GNU/Linux systems work as well as the confidence to explore larger,
more complex source-code-only projects.
-----------------------------------------------------------------------------
Table of Contents
Legal Information
1. Copyright and License
2. Disclaimer
Introduction
1. About Pocket Linux
2. Prerequisite Skills
3. Project Format
4. Help & Support
5. Feedback
1. Project Initiation
1.1. A Brief History of GNU/Linux
1.2. The Goal of Pocket Linux
1.3. Working Within The Constraints
2. A Simple Prototype
2.1. Analysis
2.2. Design
2.3. Construction
2.4. Implementation
3. Saving Space
3.1. Analysis
3.2. Design
3.3. Construction
3.4. Implementation
4. Some Basic Utilities
4.1. Analysis
4.2. Design
4.3. Construction
4.4. Implementation
5. Checking and Mounting Disks
5.1. Analysis
5.2. Design
5.3. Construction
5.4. Implementation
6. Automating Startup & Shutdown
6.1. Analysis
6.2. Design
6.3. Construction
6.4. Implementation
7. Enabling Multiple Users
7.1. Analysis
7.2. Design
7.3. Construction
7.4. Implementation
8. Filling in the Gaps
8.1. Analysis
8.2. Design
8.3. Construction
8.4. Implementation
9. Project Wrap Up
9.1. Celebrating Accomplishments
9.2. Planning Next Steps
A. Hosting Applications
A.1. Analysis
A.2. Design
A.3. Construction
A.4. Implementation
B. GNU Free Documentation License
B.1. PREAMBLE
B.2. APPLICABILITY AND DEFINITIONS
B.3. VERBATIM COPYING
B.4. COPYING IN QUANTITY
B.5. MODIFICATIONS
B.6. COMBINING DOCUMENTS
B.7. COLLECTIONS OF DOCUMENTS
B.8. AGGREGATION WITH INDEPENDENT WORKS
B.9. TRANSLATION
B.10. TERMINATION
B.11. FUTURE REVISIONS OF THIS LICENSE
B.12. ADDENDUM: How to use this License for your documents
-----------------------------------------------------------------------------
Legal Information
1. Copyright and License
This document, Pocket Linux Guide, is copyright (c) 2003 - 2005 by David
Horton. Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or any
later version published by the Free Software Foundation; with no Invariant
Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of
the license is available at the end of this document.
Linux is a registered trademark of Linus Torvalds.
-----------------------------------------------------------------------------
2. Disclaimer
This documentation is provided as-is with no warranty of any kind, either
expressed or implied, including, but not limited to, the implied warranties
of merchantability and fitness for a particular purpose. Use the concepts,
examples and information at your own risk. The author(s) do not take any
responsibility for damages that may arise from the use of this document.
All copyrights are held by their respective owners, unless specifically noted
otherwise. Use of a term in this document should not be regarded as affecting
the validity of any trademark or service mark. Naming of particular products
or brands should not be seen as endorsements.
-----------------------------------------------------------------------------
Introduction
1. About Pocket Linux
The Pocket Linux Guide demonstrates how to build a small console-based GNU/
Linux system using only source code and a couple of diskettes. It is intended
for Linux users who would like to gain a deeper understanding about how their
system works beneath the shroud of distribution specific features and tools.
-----------------------------------------------------------------------------
2. Prerequisite Skills
This guide is intended for intermediate to advanced Linux users. It is not
intentionally obscure, but certain assumptions about the readers skill level
are made. Success with this guide depends in part on being able to perform
the following tasks:
<EFBFBD><EFBFBD>*<2A>Use basic shell commands
<EFBFBD><EFBFBD>*<2A>Reference man and info pages
<EFBFBD><EFBFBD>*<2A>Build a custom Linux kernel
<EFBFBD><EFBFBD>*<2A>Compile source code using make and related tools
-----------------------------------------------------------------------------
3. Project Format
The Pocket Linux Guide takes a hands-on approach to learning. The guide is
written with each chapter building a piece of an overall project. Chapters
are further broken into sections of Analysis, Design, Construction and
Implementation. This format is derived from Rapid Application Development
(RAD) methodology. Without going into detail about design methodologies, the
sections may be summed up as follows.
<EFBFBD><EFBFBD>*<2A>The Analysis section gives a high-level overview of what is to be
accomplished in each chapter. It will introduce the tasks that need to be
completed and why they are important to the overall system.
<EFBFBD><EFBFBD>*<2A>The Design section defines the source code packages, files and
configuration necessary to address the requirements set forth in the
Analysis section. Much of the theory of why certain system files exist
and what their purpose is can be found here.
<EFBFBD><EFBFBD>*<2A>The Construction section is where all the hands-on action takes place.
This section goes into detail about building source code and configuring
the system files.
<EFBFBD><EFBFBD>*<2A>The Implementation section will test the proper operation of the project
at the end of each chapter. Often there are a few shell commands to
perform and samples of expected screen outputs are given.
Readers interested in learning more about RAD may want to consult a textbook
covering systems analysis and design or visit the following University of
California, Davis website on the subject: [http://sysdev.ucdavis.edu/WEBADM/
document/rad-stages.htm] http://sysdev.ucdavis.edu/WEBADM/document/
rad-stages.htm.
-----------------------------------------------------------------------------
4. Help & Support
Readers are encouraged to visit the Pocket Linux Resource Site at [http://
pocket-linux.sourceforge.net] http://pocket-linux.sourceforge.net/. The
resource site is home to:
<EFBFBD><EFBFBD>*<2A>Information about the Pocket Linux mailing list.
<EFBFBD><EFBFBD>*<2A>A web-based troubleshooting forum where readers can ask questions and
give tips to others.
<EFBFBD><EFBFBD>*<2A>A collection of diskette images for various chapters.
<EFBFBD><EFBFBD>*<2A>Additional projects that may be of interest to Pocket Linux Guide
readers.
-----------------------------------------------------------------------------
5. Feedback
For technical questions about Pocket Linux please use the mailing list or the
troubleshooting forum on the [http://pocket-linux.sourceforge.net] resource
site. General comments and suggestions may be sent to the mailing list or
emailed to the author directly.
-----------------------------------------------------------------------------
Chapter 1. Project Initiation
1.1. A Brief History of GNU/Linux
In the early 90's GNU/Linux systems consisted of little more than a
beta-quality Linux kernel and a small collection of software ported from the
GNU project. It was a true hacker's operating system. There were no CD-ROM's
or GUI installation tools; everything had to be compiled and configured by
the end user. Being a Linux Expert meant knowing your system inside and out.
Toward the middle of the decade several GNU/Linux distributions began
appearing. One of the first was [http://www.slackware.org] Slackware in 1993
and since then there have been many others. Even though there are many
"flavors" of Linux today, the main purpose of the distribution remains the
same. The distribution automates many of the tasks involved in GNU/Linux
installation and configuration taking the burden off of the system
administrator. Being a Linux Expert now means knowing which button to click
in the GUI administration tool.
Recently there has been a yearn for a return to the "good old days" of Linux
when men were men, sysadmins were hardcore geeks and everything was compiled
from source code. A notable indication of this movement was the publication
of the Linux-From-Scratch-HOWTO version 1.0 by Gerard Beekmans in 1999. Being
a Linux Expert once again means knowing how to do it yourself.
For more historical information, see Ragib Hasan's "History of Linux" at
[http://netfiles.uiuc.edu/rhasan/linux] http://netfiles.uiuc.edu/rhasan/linux
-----------------------------------------------------------------------------
1.2. The Goal of Pocket Linux
The purpose of Pocket Linux is to support and encourage people who wish to
explore Linux by building a GNU/Linux system from nothing but source code.
Pocket Linux is not intended to be a full featured system, but rather to give
the reader a taste of what is involved in building an operating system from
source code. After completing the Pocket Linux system the reader should have
enough knowledge to confidently build almost any project using only source
code. Given this direction we can put a few constraints on the project.
<EFBFBD><EFBFBD>*<2A>The main focus should be learning. The project should not just describe
how to do something, it should also describe why it should be done.
<EFBFBD><EFBFBD>*<2A>The required time commitment should be minimal and manageable.
<EFBFBD><EFBFBD>*<2A>The project should not require any investment in additional hardware or
reconfiguration of existing hardware to set up a lab environment.
<EFBFBD><EFBFBD>*<2A>Readers should not need to know any programming languages in order to
complete the project.
<EFBFBD><EFBFBD>*<2A>To remain true to the spirit of GNU/Linux, all software used in the
project should be covered under the GNU/GPL or another, similarly
liberal, open-source license.
-----------------------------------------------------------------------------
1.3. Working Within The Constraints
The Pocket Linux project gets its name from the fact that the bulk of the
project fits onto two diskettes making it possible to carry the entire,
working system around in one's pocket. This has the advantage of not
requiring any additional hardware since any PC can be booted from the
diskettes without disrupting any OS that exists on the hard drive. Using
diskettes also partially addresses the aspect of time commitment, because the
project size and complexity is necessarily limited by the 1.44 Megabyte size
of the installation media.
To further reduce the time commitment, the Pocket Linux project is divided
into several phases, each one chapter in length. Each phase builds only a
small piece of the overall project, but at the same time the conclusion of
each chapter results in a self-contained, working system. This step-by-step
approach should allow readers to pace themselves and not feel the need to
rush to see results.
Chapters are further subdivided into four sections. The first two sections,
analysis and design, focus on the theory of what is to be accomplished in
each phase and why. The last two sections, construction and implementation,
detail the steps needed to do the actual building. Advanced readers, who may
be familiar with the theories laid out in a particular chapter are encouraged
to gloss over the analysis and design sections in the interest of time. The
separation of theory from hands-on exercises should allow readers of all
skill levels to complete the project without feeling either completely lost
or mired in too much detail.
Finally, the Pocket Linux project will strive to use GNU/GPL software when
possible and other open-source licensed software when there is no GNU/GPL
alternative. Also, Pocket Linux will never require any programming more
complex than a BASH shell script.
-----------------------------------------------------------------------------
Chapter 2. A Simple Prototype
2.1. Analysis
Since this is the first phase of the project it will be kept very simple. The
goal here is not to create the ultimate GNU/Linux system on the first try.
Instead, we will be building a very minimal, working system to be used as a
building block in subsequent phases of the project. Keeping this in mind, we
can list a few goals for phase one.
<EFBFBD><EFBFBD>*<2A>Keep it simple to avoid stressing out.
<EFBFBD><EFBFBD>*<2A>Build something that works for instant gratification.
<EFBFBD><EFBFBD>*<2A>Make something that it is useful in later phases of the project.
-----------------------------------------------------------------------------
2.2. Design
2.2.1. Simplification
Take a moment to skim through the Bootdisk-HOWTO or the
From-PowerUp-to-BASH-Prompt-HOWTO. These HOWTO documents can be found online
at [http://www.tldp.org/docs.html#howto] http://www.tldp.org/docs.html#howto.
Both documents offer an excellent view of what it takes to get a GNU/Linux
system up and running. There is also a lot of information to digest. Remember
that one of our goals is, "keep it simple to avoid stressing out," so we want
to ignore everything but the absolutely critical pieces of a boot / root
diskset.
Basically it boils down to the following required items:
<EFBFBD><EFBFBD>*<2A>A boot loader
<EFBFBD><EFBFBD>*<2A>The Linux kernel
<EFBFBD><EFBFBD>*<2A>A shell
<EFBFBD><EFBFBD>*<2A>Some /dev files
We don't even need an init daemon. The kernel can be told to run the shell
directly by passing it an option through the boot loader.
For easy construction we will build a two-disk boot / root set rather than
trying to get everything onto a single diskette. The boot loader and kernel
will go on the boot disk and the shell will reside on the root disk.
-----------------------------------------------------------------------------
2.2.2. Boot Disk
For the boot disk we simply need to install the GRUB bootloader and a Linux
kernel. We will need to use a kernel that does not require modules for the
hardware we need to access. Mainly, it should have compiled-in support for
the floppy drive, ram disk, second extended filesystem, proc filesystem, ELF
binaries, and a text-based console. If such a kernel is not available, it
will need to be built from source code. Kwan Lowe's Kernel Rebuild Guide is a
good reference for this task, however we can ignore the sections that deal
with modules and the initial ramdisk.
-----------------------------------------------------------------------------
2.2.3. Root Disk
For the root disk we will need a floppy that has been prepared with a
filesystem. We will also need a BASH shell that is statically-linked so we
can avoid the additional complexities of shared libraries. The configure
program in the BASH source code recognizes the --enable-static-link option
for this feature. We will also be using the --enable-minimal-config option to
keep the BASH binary down to a manageable size. Additional requirements for
the root disk are a /dev directory and a device file for the console. The
console device is required for BASH to be able to communicate with the
keyboard and video display.
-----------------------------------------------------------------------------
2.2.4. CPU Compatibility
There is one other, less obvious requirement to keep in mind and that is CPU
compatibility. Each generation of CPU features a more complex architecture
than its predecessor. Late generation chips have additional registers and
instructions when compared to an older 486 or 386. So a kernel optimized for
a new, fast 6x86 machine will not run on an older box. (See the README file
in the Linux kernel source code for details.) A BASH shell built for a 6x86
will probably not run on an older processor either. To avoid this problem, we
can choose the 386 as a lowest common denominator CPU and build all the code
for that architecture.
-----------------------------------------------------------------------------
2.3. Construction
In this section, we will be building the actual boot disk and root disk
floppies. Lines preceded by bash# indicate a shell command and lines starting
with grub> indicate a command typed within the grub shell.
-----------------------------------------------------------------------------
2.3.1. Prepare the boot disk media
Insert a blank diskette labeled "boot disk".
Note It may be necessary to erase the "blank" diskette if it comes factory
pre-formatted for another, non-Linux operating system. This can be done
using the command dd if=/dev/zero of=/dev/fd0 bs=1k count=1440
bash# mke2fs -m0 /dev/fd0
bash# mount /dev/fd0 /mnt
-----------------------------------------------------------------------------
2.3.2. Build the GRUB bootloader
Get the GRUB source code from [ftp://alpha.gnu.org/gnu/grub/] ftp://
alpha.gnu.org/gnu/grub/ and unpack it into the /usr/src directory.
Configure and build the GRUB source code for an i386 processor by using the
following commands:
bash# cd /usr/src/grub-0.95
bash# export CC="gcc -mcpu=i386"
bash# ./configure --host=i386-pc-linux-gnu --without-curses
bash# make
-----------------------------------------------------------------------------
2.3.3. Copy the bootloader files to diskette
Normally, after compiling source code, one would use the command make install
to copy the finished files to their proper destinations in the filesystem.
However, using make install does not work well with small media like the
floppy disks we are using. The problem is that there are many files in a
package besides the actual binaries that get the job done. For example, there
are often man or info pages that provide documentation. These extra files can
take up more space than we can spare on the diskette. We can work around this
limitation by copying essential files manually rather than using make install
.
For GRUB to boot we will need to copy the stage1 and stage2 bootloader files
to the /boot/grub directory on the boot floppy.
bash# mkdir -p /mnt/boot/grub
bash# cp /usr/src/grub-0.95/stage1/stage1 /mnt/boot/grub
bash# cp /usr/src/grub-0.95/stage2/stage2 /mnt/boot/grub
-----------------------------------------------------------------------------
2.3.4. Finish bootloader installation
Once the bootloader's files are copied to the boot disk we can enter the grub
shell to finish the installation.
bash# /usr/src/grub-0.95/grub/grub
grub> root (fd0)
grub> setup (fd0)
grub> quit
-----------------------------------------------------------------------------
2.3.5. Build the Linux kernel
The steps for building the kernel were tested using Linux kernel version
2.4.26 and should work any 2.4.x or 2.6.x kernel. The latest version of the
kernel source code may be downloaded from [http://www.kernel.org/] http://
www.kernel.org/ or one of its mirrors.
Note The instructions below are very brief and are intended for someone who
has previous experience building custom kernels. A more detailed
explanation of the kernel building process can be found in the Kernel
Rebuild Guide by Kwan Lowe.
bash# cd /usr/src/linux
bash# make menuconfig
Be sure to configure support for the following:
<EFBFBD><EFBFBD>*<2A>386 processor
<EFBFBD><EFBFBD>*<2A>Console on virtual terminal (2.4.x kernels only)
<EFBFBD><EFBFBD>*<2A>ELF binaries
<EFBFBD><EFBFBD>*<2A>Floppy disk
<EFBFBD><EFBFBD>*<2A>proc filesystem
<EFBFBD><EFBFBD>*<2A>RAM disk with a default size of 4096K
<EFBFBD><EFBFBD>*<2A>Second extended (ext2) filesystem
<EFBFBD><EFBFBD>*<2A>VGA console
bash# make dep
bash# make clean
bash# make bzImage
-----------------------------------------------------------------------------
2.3.6. Copy the kernel to diskette
bash# cp /usr/src/linux/arch/i386/boot/bzImage /mnt/boot/vmlinuz
-----------------------------------------------------------------------------
2.3.7. Unmount the boot disk
bash# cd /
bash# umount /mnt
-----------------------------------------------------------------------------
2.3.8. Prepare the root disk media
Insert a blank diskette labeled "root disk".
bash# mke2fs -m0 /dev/fd0
bash# mount /dev/fd0 /mnt
-----------------------------------------------------------------------------
2.3.9. Build BASH
Get the bash-3.0 source code package from [ftp://ftp.gnu.org/gnu/bash/] ftp:/
/ftp.gnu.org/gnu/bash/ and untar it into the /usr/src directory.
Build BASH for an i386 CPU with the following commands:
bash# cd /usr/src/bash-3.0
bash# export CC="gcc -mcpu=i386"
bash# ./configure --enable-static-link \
--enable-minimal-config --host=i386-pc-linux-gnu
bash# make
bash# strip bash
-----------------------------------------------------------------------------
2.3.10. Copy BASH to the root disk
bash# mkdir /mnt/bin
bash# cp bash /mnt/bin/bash
bash# ln -s bash /mnt/bin/sh
-----------------------------------------------------------------------------
2.3.11. Create device files that BASH needs
bash# mkdir /mnt/dev
bash# mknod /mnt/dev/console c 5 1
-----------------------------------------------------------------------------
2.3.12. Unmount the root disk
bash# cd /
bash# umount /mnt
-----------------------------------------------------------------------------
2.4. Implementation
2.4.1. System startup
Follow these steps to boot the system:
<EFBFBD><EFBFBD>*<2A>Restart the PC with the boot disk in the floppy drive.
<EFBFBD><EFBFBD>*<2A>When the grub> prompt appears, type kernel (fd0)/boot/vmlinuz init=/bin/
sh root=/dev/fd0 load_ramdisk=1 prompt_ramdisk=1 and press Enter.
<EFBFBD><EFBFBD>*<2A>After the kernel loads, type boot and press Enter.
<EFBFBD><EFBFBD>*<2A>Insert the root disk when prompted.
If all goes well the screen should look something like the example shown
below.
GNU GRUB version 0.95
grub> kernel (fd0)/boot/vmlinuz init=/bin/sh root=/dev/fd0 load_ramdisk=1 prompt_ramdisk=1
[Linux-bzImage, setup=0xc00, size=0xce29b]
grub> boot
Linux version 2.4.26
..
.. [various kernel messages]
..
VFS: Insert root floppy disk to be loaded into RAM disk and press ENTER
RAMDISK: ext2 filesystem found at block 0
RAMDISK: Loading 1440 blocks [1 disk] into ram disk... done.
VFS: Mounted root (ext2 filesystem) readonly.
Freeing unused kernel memory: 178k freed
# _
-----------------------------------------------------------------------------
2.4.2. Testing what works
Try out a few of BASH's built-in commands to see if things are working
properly.
bash# echo "Hello World"
bash# cd /
bash# pwd
bash# echo *
-----------------------------------------------------------------------------
2.4.3. Noting what does not work
Try out a few other familiar commands.
bash# ls /var
bash# mkdir /var/tmp
Notice that only commands internal to BASH actually work and that external
commands like ls and mkdir do not work at all. This shortcoming is something
that can be addressed in a future phase of the project. For now we should
just enjoy the fact that our prototype boot / root diskset works and that it
was not all that hard to build.
-----------------------------------------------------------------------------
2.4.4. System shutdown
Remove the diskette from fd0 and restart the system using CTRL-ALT-DELETE.
-----------------------------------------------------------------------------
Chapter 3. Saving Space
3.1. Analysis
One of the drawbacks in the prototype phase of the project was that the
diskset was not all that useful. The only commands that worked were the ones
built into the BASH shell. We could improve our root disk by installing
commands like cat, ls, mv, rm and so on. Unfortunately, we are short on
space. The current root disk has no shared libraries so each utility would
have to be statically-linked just like the BASH shell. A lot of big binaries
together with a static shell will rapidly exceed the tiny 1.44M of available
disk space. So our main goal in this phase should be to maximize space
savings on the root disk and pave the way for expanded functionality in the
next phase.
-----------------------------------------------------------------------------
3.2. Design
Take another look at the Bootdisk-HOWTO and notice how many utilities can be
squeezed onto a 1.44M floppy. There are three things that make this possible.
One is the use of shared libraries. The second is stripped binaries. And the
third is the use of a compressed filesystem. We can use all of these
techniques to save space on our root disk.
-----------------------------------------------------------------------------
3.2.1. Shared Libraries
First, in order to use shared libraries we will need to rebuild the BASH
shell. This time we will configure it without using the --enable-static-link
option. Once BASH is rebuilt we need to figure out which libraries it is
linked with and be sure to include them on the root disk. The ldd command
makes this job easy. By typing ldd bash on the command-line we can see a list
of all the shared libraries that BASH uses. As long as all these libraries
are copied to the root disk, the new BASH build should work fine.
-----------------------------------------------------------------------------
3.2.2. Stripped Binaries
Next, we should strip any binaries that get copied to the root disk. The
manpage for strip does not give much description of what it does other than
to say, "strip discards all symbols from the object files." It seems like
removing pieces of a binary would render it useless, but this is not the
case. The reason it works is because a large number of these discarded
symbols are used for debugging. While debugging symbols are very helpful to
programmers working to improve the code, they do not do much for the average
end-user other than take up more disk space. And since space is at a premium,
we should definitely remove as many symbols as possible from BASH and any
other binaries before we copy over them to the ramdisk.
The process of stripping files to save space also works with shared library
files. But when stripping libraries it is important to use the
--strip-unneeded option so as not to break them. Using --strip-unneeded
shrinks the file size, but leaves the symbols needed for relocation intact
which is something that shared libraries need to function properly.
-----------------------------------------------------------------------------
3.2.3. Compressed Root Filesystem
Finally, we can tackle the problem of how to build a compressed root
filesystem. The Bootdisk-HOWTO suggests three ways of constructing a
compressed root filesystem using either a ramdisk, a spare hard drive
partition or a loopback device. This project will concentrate on using the
ramdisk approach. It seems logical that if the root filesystem is going to be
run from a ramdisk, it may as well be built on a ramdisk. All we have to do
is create a second extended filesystem on a ramdisk device, mount it and copy
files to it. Once the filesystem is populated with all the files that the
root disk needs, we simply unmount it, compress it and write it out to
floppy.
Note For this to work, we need to make sure the system used for building has
ramdisk support. If ramdisk is not available it is also possible to use
a loopback device. See the Bootdisk-HOWTO for more information on using
loopback devices.
-----------------------------------------------------------------------------
3.3. Construction
This section is written using ramdisk seven (/dev/ram7) to build the root
image. There is nothing particularly special about ramdisk seven and it is
possible to use any of the other available ramdisks provided they are not
already in use.
-----------------------------------------------------------------------------
3.3.1. Create a ramdisk
bash# dd if=/dev/zero of=/dev/ram7 bs=1k count=4096
bash# mke2fs -m0 /dev/ram7 4096
bash# mount /dev/ram7 /mnt
-----------------------------------------------------------------------------
3.3.2. Rebuild the BASH shell
bash# cd /usr/src/bash-3.0
bash# make distclean
bash# export CC="gcc -mcpu=i386"
bash# ./configure --enable-minimal-config --host=i386-pc-linux-gnu
bash# make
bash# strip bash
-----------------------------------------------------------------------------
3.3.3. Determine which libraries are required
bash# ldd bash
View the output from the ldd command. It should look similar to the example
below.
bash# ldd bash
libdl.so.2 => /lib/libdl.so.2 (0x4001d000)
libc.so.6 => /lib/libc.so.6 (0x40020000)
/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
Note Some systems may have a slightly different library set up. For example,
you may see libc.so.6 => /lib/tls/libc.so.6 rather than libc.so.6 => /
lib/libc.so.6 as shown in the example. If your ldd output does not match
the example then use the path given by your ldd command when completing
the next step.
-----------------------------------------------------------------------------
3.3.4. Copy BASH and its libraries to the ramdisk
bash# mkdir /mnt/bin
bash# cp bash /mnt/bin
bash# ln -s bash /mnt/bin/sh
bash# mkdir /mnt/lib
bash# strip --strip-unneeded -o /mnt/lib/libdl.so.2 /lib/libdl.so.2
bash# strip --strip-unneeded -o /mnt/lib/libc.so.6 /lib/libc.so.6
bash# strip --strip-unneeded -o /mnt/lib/ld-linux.so.2 /lib/ld-linux.so.2
bash# chmod +x /mnt/lib/ld-linux.so.2
Note Using strip -o might seem an odd way to copy library files from the
development system to the ramdisk. What it does is strip the symbols
while the file is in transit from the source location to the
destination. This has the effect of stripping symbols from the library
on the ramdisk without altering the libraries on the development system.
Unfortunately file permissions are lost when copying libraries this way
which is why the chmod +x command is then used to set the execute flag
for the rootdisk's dynamic loader.
-----------------------------------------------------------------------------
3.3.5. Create a console device
bash# mkdir /mnt/dev
bash# mknod /mnt/dev/console c 5 1
-----------------------------------------------------------------------------
3.3.6. Compress the ramdisk image
bash# cd /
bash# umount /dev/ram7
bash# dd if=/dev/ram7 of=~/phase2-image bs=1k count=4096
bash# gzip -9 ~/phase2-image
-----------------------------------------------------------------------------
3.3.7. Copy the compressed image to diskette
Insert the floppy labeled "root disk" into drive fd0.
bash# dd if=~/phase2-image.gz of=/dev/fd0 bs=1k
-----------------------------------------------------------------------------
3.4. Implementation
Successful implementation of this phase is probably the most difficult part
of the Pocket Linux Guide. If you need help getting things to work please
visit the Pocket Linux Guide Resource Site to browse the troubleshooting
forum and subscribe to the mailing list.
-----------------------------------------------------------------------------
3.4.1. System startup
Follow these steps to boot:
<EFBFBD><EFBFBD>*<2A>Restart the PC using the boot disk from the previous chapter.
<EFBFBD><EFBFBD>*<2A>At the grub> prompt, type kernel (fd0)/boot/vmlinuz init=/bin/sh root=/
dev/fd0 load_ramdisk=1 prompt_ramdisk=1 and press Enter.
<EFBFBD><EFBFBD>*<2A>Type boot at the grub> prompt and press Enter.
<EFBFBD><EFBFBD>*<2A>Insert the new, compressed root disk when prompted.
The screen output should be similar to the following example:
GNU GRUB version 0.95
grub> kernel (fd0)/boot/vmlinuz init=/bin/sh root=/dev/fd0 load_ramdisk=1 prompt_ramdisk=1
[Linux-bzImage, setup=0xc00, size=0xce29b]
grub> boot
Linux version 2.4.26
..
.. [various kernel messages]
..
VFS: Insert root floppy disk to be loaded into RAM disk and press ENTER
RAMDISK: Compressed image found at block 0
VFS: Mounted root (ext2 filesystem) readonly.
Freeing unused kernel memory: 178k freed
# _
-----------------------------------------------------------------------------
3.4.2. Verify results
If the implementation was successful, this new root disk should behave
exactly like the root disk from the previous chapter. The key difference is
that this compressed root disk has much more room to grow and we will put
this extra space to good use in the next phase of the project.
-----------------------------------------------------------------------------
3.4.3. System shutdown
Remove the diskette from fd0 and restart the system using CTRL-ALT-DELETE.
-----------------------------------------------------------------------------
Chapter 4. Some Basic Utilities
4.1. Analysis
In the previous chapter it might seem like we did not accomplish very much. A
lot of energy was expended redesigning the root disk, but the functionality
is basically the same as in the initial prototype phase. The root disk still
does not do very much. But we did make significant improvements when it comes
to space savings. In this chapter we will put that extra space to good use
and start cramming the root disk with as many utilities as it can hold.
The first two root disks we built only had shell built-in commands like echo
and pwd. This time it would be nice to have some of the commonly used
external commands like cat, ls, mkdir, rm and such on the root disk. Keeping
this in mind we can define the goals for this phase as follows:
<EFBFBD><EFBFBD>*<2A>Retain all of the functionality from the previous root disk.
<EFBFBD><EFBFBD>*<2A>Add some of the commonly used external commands.
-----------------------------------------------------------------------------
4.2. Design
4.2.1. Determining Required Commands
The first question that might come to mind is, "How do we know which commands
are needed?" It is possible to just start with cat and ls then install other
commands as we discover a need for them. But this is terribly inefficient. We
need a plan or a blueprint to work from. For this we can turn to the
Filesystem Hierarchy Standard (FHS) available from [http://www.pathname.com/
fhs/] http://www.pathname.com/fhs/. The FHS dictates which commands should be
present on a Linux system and where they should be placed in the directory
structure.
-----------------------------------------------------------------------------
4.2.2. Locating Source Code
The next logical question is, "Now that we know what we need, where do we get
the source code?" One way to find the answer to this question is to check the
manpages. We can either search the manpages included with one of the popular
GNU/Linux distributions or use one of the manpage search engines listed at
[http://www.tldp.org/docs.html#man] http://www.tldp.org/docs.html#man. One
thing that should tip us off as to where to find the source code for a
particular command is the email address listed for reporting bugs. For
example the cat manpage lists bug-textutils@gnu.org. From this email address
we can deduce that cat is part of the textutils package from [http://gnu.org]
GNU.
-----------------------------------------------------------------------------
4.2.3. Leveraging FHS
So let's look at the FHS requirements for the /bin directory. The first few
commands in the list are cat, chgrp, chmod, chown and cp. We already know
that cat is part of GNU's textutils. Using the next few commands as keywords
in a manpage search we discover that we need GNU's fileutils package for
chmod, chgrp, chown and cp. In fact quite a few of the commands in /bin come
from GNU's fileutils. The date command also comes from a GNU package called
sh-utils. So a good way to tackle the problem of finding source code might be
to group the commands together by package as shown below.
<EFBFBD><EFBFBD>*<2A>The BASH shell -- echo, false, pwd, sh, true
<EFBFBD><EFBFBD>*<2A>GNU textutils -- cat
<EFBFBD><EFBFBD>*<2A>GNU fileutils -- chgrp, chmod, chown, cp, dd, df, ln, ls, mkdir, mknod,
mv, rm, rmdir, sync
<EFBFBD><EFBFBD>*<2A>GNU sh-utils -- date, hostname, stty, su, uname
These four packages do not contain all of the commands in the /bin directory,
but they do represent of over 70% of them. That should be enough to
accomplish our goal of adding some of the commonly used external commands. We
can worry about the other commands in later phases of the project.
-----------------------------------------------------------------------------
4.2.4. Downloading Source Code
To fetch the source code we simply need to connect to [ftp://ftp.gnu.org/gnu]
GNU's FTP site and navigate to the appropriate package directory.
When we get to the directory for textutils there are several versions
available. There is also a note informing us that the package has been
renamed to coreutils. The same message about coreutils appears in the
fileutils and sh-utils directories as well. So instead of downloading three
separate packages we can get everything in one convenient bundle in the
coreutils directory.
-----------------------------------------------------------------------------
4.3. Construction
Rather than copying files directly to the ramdisk, we can make things easier
by setting up a staging area. The staging area will give us room to work
without worrying about the space constraints of the ramdisk. It will also
provide a way to save our work and make it easier to enhance the rootdisk in
later phases of the project.
The staging procedure will work like this:
1. Create a directory structure as defined in the FHS.
2. Copy in the files from phase 2's root disk.
3. Build the new package from source code.
4. Install files into the correct FHS directories.
5. Strip the binaries to save space.
6. Check library dependencies.
7. Copy to the whole directory structure to the ramdisk.
8. Compress the ramdisk and write it out to floppy.
-----------------------------------------------------------------------------
4.3.1. Create a staging area
bash# mkdir ~/staging
bash# cd ~/staging
bash# mkdir bin boot dev etc home lib mnt opt proc root sbin tmp usr var
bash# mkdir var/log var/run
-----------------------------------------------------------------------------
4.3.2. Copy contents of phase 2 rootdisk
bash# dd if=~/phase2-image.gz | gunzip -c > /dev/ram7
bash# mount /dev/ram7 /mnt
bash# cp -dpR /mnt/* ~/staging
bash# umount /dev/ram7
bash# rmdir ~/staging/lost+found
-----------------------------------------------------------------------------
4.3.3. Install binaries from GNU coreutils
Download a recent version of coreutils from [ftp://ftp.gnu.org/gnu/coreutils
/] ftp://ftp.gnu.org/gnu/coreutils/
bash# cd /usr/src/coreutils-5.2.1
bash# export CC="gcc -mcpu=i386"
bash# ./configure --host=i386-pc-linux-gnu
bash# make
bash# cd src
bash# cp cat chgrp chmod chown cp date dd df ~/staging/bin
bash# cp hostname ln ls mkdir mkfifo mknod ~/staging/bin
bash# cp mv rm rmdir stty su sync uname ~/staging/bin
-----------------------------------------------------------------------------
4.3.4. Copy additional libraries
Check library requirements by using ldd on some of the new binaries.
bash# ldd ~/staging/bin/cat
bash# ldd ~/staging/bin/ls
bash# ldd ~/staging/bin/su
bash# ls ~/staging/lib
Note the differences in the required libraries, as shown by the ldd command,
and the libraries present in the staging area, as shown by the ls command,
then copy any missing libraries to the staging area.
bash# cp /lib/librt.so.1 ~/staging/lib
bash# cp /lib/libpthread.so.0 ~/staging/lib
bash# cp /lib/libcrypt.so.1 ~/staging/lib
-----------------------------------------------------------------------------
4.3.5. Strip binaries and libraries
bash# strip ~/staging/bin/*
bash# strip --strip-unneeded ~/staging/lib/*
-----------------------------------------------------------------------------
4.3.6. Create a compressed root disk image
bash# cd /
bash# dd if=/dev/zero of=/dev/ram7 bs=1k count=4096
bash# mke2fs -m0 /dev/ram7 4096
bash# mount /dev/ram7 /mnt
bash# cp -dpR ~/staging/* /mnt
bash# umount /dev/ram7
bash# dd if=/dev/ram7 of=~/phase3-image bs=1k count=4096
bash# gzip -9 ~/phase3-image
Note The process for creating the compressed root disk image will change very
little throughout the remaining chapters. Writing a small script to
handle this function can be a great time saver.
-----------------------------------------------------------------------------
4.3.7. Write the root disk image to floppy
Insert the diskette labeled "root disk" into drive fd0.
bash# dd if=~/phase3-image.gz of=/dev/fd0 bs=1k
-----------------------------------------------------------------------------
4.4. Implementation
We will need to have a read-write filesystem in order for some of the
commands to work. The kernel's normal behavior is to mount root as read-only,
but we can change this using a kernel option. By passing the kernel the rw
option before init=/bin/sh we will get a read-write root filesystem.
-----------------------------------------------------------------------------
4.4.1. System startup
Follow these steps to get the system running.
<EFBFBD><EFBFBD>*<2A>Boot the PC from using the GRUB boot disk.
<EFBFBD><EFBFBD>*<2A>At the grub> prompt, type kernel (fd0)/boot/vmlinuz rw init=/bin/sh root=
/dev/fd0 load_ramdisk=1 prompt_ramdisk=1.
<EFBFBD><EFBFBD>*<2A>Verify that you remembered to add the rw parameter and press Enter.
<EFBFBD><EFBFBD>*<2A>Type boot and press Enter.
<EFBFBD><EFBFBD>*<2A>Insert the recently created root disk when prompted.
The terminal display should look similar to the example below.
GNU GRUB version 0.95
grub> kernel (fd0)/boot/vmlinuz rw init=/bin/sh root=/dev/fd0 load_ramdisk=1 prompt_ramdisk=1
[Linux-bzImage, setup=0xc00, size=0xce29b]
grub> boot
Linux version 2.4.26
..
.. [various kernel messages]
..
VFS: Insert root floppy disk to be loaded into RAM disk and press ENTER
RAMDISK: Compressed image found at block 0
VFS: Mounted root (ext2 filesystem) read-write.
Freeing unused kernel memory: 178k freed
# _
-----------------------------------------------------------------------------
4.4.2. Testing new commands
Now that the system is up and running, try using some of the new commands.
bash# uname -a
bash# ls /etc
bash# echo "PocketLinux" > /etc/hostname
bash# hostname $(cat /etc/hostname)
bash# uname -n
bash# mkdir /home/stuff
bash# cd /home/stuff
If everything goes well the commands like cat, ls and hostname should work
now. Even mkdir should work since the root filesystem is mounted read-write.
Of course since we are using a ramdisk, any changes will be lost once the PC
is reset.
-----------------------------------------------------------------------------
4.4.3. System shutdown
Remove the diskette from fd0 and restart the system using CTRL-ALT-DELETE.
-----------------------------------------------------------------------------
Chapter 5. Checking and Mounting Disks
5.1. Analysis
In the previous chapter we added many new commands by installing coreutils
and as a result the root disk has a lot more functionality. But there are
still a few things lacking. One thing that really stands out is that there
was no way to mount disks. In order to get a read-write root filesystem we
had to resort to passing the rw kernel parameter at the grub> prompt. This is
fine for an emergency situation, but a normal system boot process should do
things differently.
Most GNU/Linux distributions take several steps to mount filesystems.
Watching the boot process or digging into the startup scripts on one of the
popular Linux distributions reveals the following sequence of events:
1. The kernel automatically mounts the root filesystem as read-only.
2. All local filesystems are checked for errors.
3. If filesystems are clean, root is remounted as read-write.
4. The rest of the local filesystems are mounted.
5. Network filesystems are mounted.
So far our Pocket Linux system can do step one and that is it. If we want to
have a professional looking boot / root diskset we will have to do better
than one out of five. In this phase of the project we will work on steps two
and three. Steps four and five can wait. Since this is a diskette-based
system, there really are no other filesystems to mount besides root.
Taking into account all of the above information, the goals for this phase
are defined as follows:
<EFBFBD><EFBFBD>*<2A>A way to check filesystem integrity.
<EFBFBD><EFBFBD>*<2A>The ability to mount filesystems.
<EFBFBD><EFBFBD>*<2A>A script to automate checking and mounting of local filesystems.
-----------------------------------------------------------------------------
5.2. Design
5.2.1. Determining necessary utilities.
We can use the Filesystem Hierarchy Standard (FHS) document to help find the
names of utilities we need and where they reside in the directory structure.
The FHS /sbin directory lists fsck and something called fsck.* for checking
filesystems. Since we are using a Second Extended (ext2) filesystem the fsck.
* becomes fsck.ext2 for our purposes. Mounting filesystems is done using the
commands mount and umount in the /bin directory. However, the name of a
script to automatically mount local filesystems cannot be found. On most
systems this type of script is in the /etc directory, but while FHS does list
requirements for /etc, it does not currently make recommendations for startup
scripts. Several GNU/Linux distributions use /etc/init.d as the place to hold
startup scripts so we will put our filesystem mounting script there.
-----------------------------------------------------------------------------
5.2.2. Finding source code
In the previous chapter we used manpages to help us find source code. In this
chapter we will use a tool called the Linux Software Map (LSM). LSM is a
database of GNU/Linux software that tracks such things as package name,
author, names of binaries that make up the package and download sites. Using
an LSM search engine we can locate packages using command names as keywords.
If we search Ibiblio's Linux Software Map (LSM) at [http://www.ibiblio.org/
pub/Linux/] http://www.ibiblio.org/pub/Linux/ for the keyword "fsck" we get a
large number of matches. Since we are using a Second Extended filesystem,
called ext2 for short, we can refine the search using "ext2" as a keyword.
Supplying both keywords to the LSM search engine comes up with a package
called e2fsprogs. Looking at the LSM entry for e2fsprogs we find out that
this package contains the utilities e2fsck, mke2fs, dumpe2fs, fsck and more.
We also find out that the LSM entry for e2fsprogs has not been updated for a
while. There is almost certainly a newer version out there somewhere. Another
good Internet resource for source code is SourceForge at [http://
sourceforge.net/] http://sourceforge.net/. Using the keyword "e2fsprogs" in
the SourceForge search engine results in a much newer version of e2fsprogs.
Finding fsck was quite an adventure, but now we can move on to finding mount
and umount. A search on LSM comes up with a number of matches, but most of
them point to various versions of a package called util-linux. All we have to
do is scroll through and pick the most recent release. The LSM entry for
util-linux lists a lot of utilities besides just mount and umount. We should
definitely scan through the list to see if any of the other util-linux
commands show up in the FHS requirements for /bin and /sbin.
Below is a list of packages we have gathered so far and the utilities that
match up with FHS.
<EFBFBD><EFBFBD>*<2A>e2fsprogs -- fsck, fsck.ext2 (e2fsck), mkfs.ext2 (mke2fs)
<EFBFBD><EFBFBD>*<2A>util-linux -- dmesg, getty (agetty), kill, login, mount, swapon, umount
-----------------------------------------------------------------------------
5.2.3. Automating fsck and mount
Now that we have fsck and mount commands we need to come up with a shell
script to automate checking and mounting the local filesystems. An easy way
to do this would be to write a short, two line script that calls fsck and
then mount. But, what if the filesystems are not clean? The system should
definitely not try to mount a corrupted filesystem. Therefore we need to
devise a way of determining the status of the filesystems before mounting
them. The manpage for fsck gives some insight into how this can be
accomplished using return codes. Basically, if fsck returns a code of zero or
one it means the filesystem is okay and a return code of two or greater means
some kind of manual intervention is needed. A simple if-then statement could
evaluate the fsck return code to determine whether or not the filesystem
should be mounted. For help on writing shell scripts we can turn to the BASH
(1) manpage and the Advanced-BASH-Scripting-Guide. Both references are freely
available from the Linux Documentation Project web site at [http://
www.tldp.org/] http://www.tldp.org/.
-----------------------------------------------------------------------------
5.2.4. File dependencies
The last thing to do is to figure out if any other files besides the binaries
are needed. We learned about using ldd to check for library dependencies in
the last phase of the project and we will use it to check the utilities in
this phase too. There are also some other files that fsck and mount will need
and the fsck(8) and mount(8) manpages give some insight into what those files
are. There is /etc/fstab that lists devices and their mount points, /etc/mtab
that keeps track of what is mounted, and a number of /dev files that
represent the various disks. We will need to include all of these to have
everything work right.
-----------------------------------------------------------------------------
5.2.4.1. /etc/fstab
The /etc/fstab file is just a simple text file that can be created with any
editor. We will need an entry for the root filesystem and for the proc
filesystem. Information about the format of this file can be found in the
fstab(5) manpage or by looking at the /etc/fstab file on any of the popular
GNU/Linux distributions.
-----------------------------------------------------------------------------
5.2.4.2. /etc/mtab
The /etc/mtab file presents a unique challenge, because it does not contain
static information like fstab. The mtab file tracks mounted filesystems and
therefore its contents change from time to time. We are particularly
interested in the state of mtab when the system first starts up, before any
filesystems are mounted. At this point /etc/mtab should be empty so we will
need to configure a startup script to create an empty /etc/mtab before any
filesystems are mounted. But it is not possible to create any files in the /
etc directory because / is read-only at startup. This creates a paradox. We
cannot create an empty mtab, because the / filesystem is not mounted as
writable and we should not mount any filesystems until we have created an
empty mtab. In order to sidestep this problem we need to do the following:
1. Remount / as read-write, but use the -n option so that mount does not
attempt to write an entry to /etc/mtab which is read-only at this point.
2. Create an empty /etc/mtab file now that the filesystem is writable.
3. Remount / as read-write again, this time using the -f option so that an
entry is written into /etc/mtab, but / is not actually mounted a second
time.
-----------------------------------------------------------------------------
5.2.4.3. Device files
The only thing left to do is to create device files. We will need /dev/ram0,
because that is where the root filesystem is located. We also need /dev/fd0
to mount other floppy disks and /dev/null for use by some of the system
commands.
-----------------------------------------------------------------------------
5.3. Construction
5.3.1. Install utilities from e2fsprogs
Download the e2fsprogs source code package from [http://sourceforge.net/
projects/e2fsprogs/] http://sourceforge.net/projects/e2fsprogs/
bash# cd /usr/src/e2fsprogs-1.35
bash# export CC="gcc -mcpu=i386"
bash# ./configure --host=i386-pc-linux-gnu
bash# make
bash# cd e2fsck
bash# cp e2fsck.shared ~/staging/sbin/e2fsck
bash# ln -s e2fsck ~/staging/sbin/fsck.ext2
bash# cd ../misc
bash# cp fsck mke2fs ~/staging/sbin
bash# ln -s mke2fs ~/staging/sbin/mkfs.ext2
-----------------------------------------------------------------------------
5.3.2. Install utilities from util-linux
Get the latest util-linux source from [ftp://ftp.win.tue.nl/pub/linux-local/
utils/util-linux/] ftp://ftp.win.tue.nl/pub/linux-local/utils/util-linux/
bash# cd /usr/src/util-linux-2.12h
Use a text editor to make the following changes to MCONFIG:
<EFBFBD><EFBFBD>*<2A>Change "CPU=$(shell uname -m)" to "CPU=i386"
<EFBFBD><EFBFBD>*<2A>Change "HAVE_SHADOW=yes" to "HAVE_SHADOW=no"
bash# ./configure
bash# make
bash# cp disk-utils/mkfs ~/staging/sbin
bash# cp fdisk/fdisk ~/staging/sbin
bash# cp login-utils/agetty ~/staging/sbin
bash# ln -s agetty ~/staging/sbin/getty
bash# cp login-utils/login ~/staging/bin
bash# cp misc-utils/kill ~/staging/bin
bash# cp mount/mount ~/staging/bin
bash# cp mount/umount ~/staging/bin
bash# cp mount/swapon ~/staging/sbin
bash# cp sys-utils/dmesg ~/staging/bin
-----------------------------------------------------------------------------
5.3.3. Check library requirements
bash# ldd ~/staging/bin/* | more
bash# ldd ~/staging/sbin/* | more
bash# ls ~/staging/lib
All of the dependencies revealed by the ldd command are for libraries already
present in the staging area so there is no need to copy anything new.
-----------------------------------------------------------------------------
5.3.4. Strip binaries to save space
bash# strip ~/staging/bin/*
bash# strip ~/staging/sbin/*
-----------------------------------------------------------------------------
5.3.5. Create additional device files
bash# mknod ~/staging/dev/ram0 b 1 0
bash# mknod ~/staging/dev/fd0 b 2 0
bash# mknod ~/staging/dev/null c 1 3
-----------------------------------------------------------------------------
5.3.6. Create the fstab and mtab files
bash# cd ~/staging/etc
Use an editor like vi, emacs or pico to create the following file and save it
as ~/staging/etc/fstab.
proc /proc proc defaults 0 0
/dev/ram0 / ext2 defaults 1 1
Create an empty mtab file.
bash# echo -n >mtab
-----------------------------------------------------------------------------
5.3.7. Write a script to check and mount local filesystems
Use an editor to create the following shell script and save it as ~/staging/
etc/init.d/local_fs:
#!/bin/sh
#
# local_fs - check and mount local filesystems
#
PATH=/sbin:/bin ; export PATH
fsck -ATCp
if [ $? -gt 1 ]; then
echo "Filesystem errors still exist! Manual intervention required."
/bin/sh
else
echo "Remounting / as read-write."
mount -n -o remount,rw /
echo -n >/etc/mtab
mount -f -o remount,rw /
echo "Mounting local filesystems."
mount -a -t nonfs,nosmbfs
fi
#
# end of local_fs
Set execute permissions on the script.
bash# chmod +x local_fs
-----------------------------------------------------------------------------
5.3.8. Create a compressed root disk image
bash# cd /
bash# dd if=/dev/zero of=/dev/ram7 bs=1k count=4096
bash# mke2fs -m0 /dev/ram7 4096
bash# mount /dev/ram7 /mnt
bash# cp -dpR ~/staging/* /mnt
bash# umount /dev/ram7
bash# dd if=/dev/ram7 of=~/phase4-image bs=1k count=4096
bash# gzip -9 ~/phase4-image
-----------------------------------------------------------------------------
5.3.9. Write the root disk image to floppy
Insert the diskette labeled "root disk" into drive fd0.
bash# dd if=~/phase4-image.gz of=/dev/fd0 bs=1k
-----------------------------------------------------------------------------
5.4. Implementation
5.4.1. System startup
Start the system using the following procedure:
<EFBFBD><EFBFBD>*<2A>Boot the PC using the floppy labeled "boot disk".
<EFBFBD><EFBFBD>*<2A>At the grub> prompt, type the usual kernel and boot commands, but without
the rw parameter this time. In other words, type kernel (fd0)/boot/
vmlinuz init=/bin/sh root=/dev/fd0 load_ramdisk=1 prompt_ramdisk=1, press
Enter then type boot and press Enter.
<EFBFBD><EFBFBD>*<2A>Put in the recently created root disk when prompted.
The output should resemble the example below:
GNU GRUB version 0.95
grub> kernel (fd0)/boot/vmlinuz init=/bin/sh root=/dev/fd0 load_ramdisk=1 prompt_ramdisk=1
[Linux-bzImage, setup=0xc00, size=0xce29b]
grub> boot
Linux version 2.4.26
..
.. [various kernel messages]
..
VFS: Insert root floppy disk to be loaded into RAM disk and press ENTER
RAMDISK: Compressed image found at block 0
VFS: Mounted root (ext2 filesystem) readonly.
Freeing unused kernel memory: 178k freed
# _
-----------------------------------------------------------------------------
5.4.2. Test the local_fs script
Run the script by typing the following commands at the shell prompt:
bash# PATH=/sbin:/bin:/etc/init.d ; export PATH
bash# cat /etc/mtab
bash# local_fs
bash# cat /etc/mtab
bash# df
If everything is working properly, then the screen output should look
something like the example below.
bash# PATH=/sbin:/bin:/etc/init.d ; export PATH
bash# cat /etc/mtab
bash# local_fs
/dev/ram0: clean 74/1024 files 3178/4096 blocks
Remounting / as read-write.
Mounting local filesystems.
bash# cat /etc/mtab
/dev/ram0 / ext2 rw 0 0
proc /proc proc rw 0 0
bash# df
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/ram0 3963 3045 918 77% /
-----------------------------------------------------------------------------
5.4.3. Create and mount additional filesystems
Procure a blank floppy disk and label it as "home". Remove the root disk
floppy and insert the "home" diskette. Type the following commands:
bash# mkfs -t ext2 /dev/fd0
bash# fsck /dev/fd0
bash# mount /dev/fd0 /home
bash# mkdir /home/floyd
bash# cd /home/floyd
bash# echo "Goodbye cruel world." > goodbye.txt
bash# cat goodbye.txt
-----------------------------------------------------------------------------
5.4.4. System shutdown
bash# cd /
bash# umount /home
Remove the diskette from fd0 and restart the system using CTRL-ALT-DELETE.
-----------------------------------------------------------------------------
Chapter 6. Automating Startup & Shutdown
6.1. Analysis
The root disk from the last chapter is looking pretty good. It has about
seventy percent of the commands that the Filesystem Hierarchy Standard (FHS)
document requires for the root filesystem. Plus it has commands for checking
and mounting filesystems. But even with all of this the root disk is far from
perfect. The list below outlines three things that could use some improvement
if the Pocket Linux system is to stand up next to the more professional
looking distributions.
1. The system currently requires the kernel parameters to be typed at the
grub> prompt in order to start properly. On any other GNU/Linux system
this is only done in an emergency situation when the system is corrupted.
2. Checking and mounting the root filesystem has to be done manually by
running a script at a shell prompt. On most modern operating systems this
function is handled automatically as part of the system start-up process.
3. Using CTRL-ALT-DELETE for system shutdown is not very graceful.
Filesystems should be unmounted and cached information should be flushed
prior to shutdown. Again, this is something that most operating systems
handle automatically.
Taking the above list into consideration, the goals for this phase are
defined as follows:
<EFBFBD><EFBFBD>*<2A>Kernel loads without manual intervention.
<EFBFBD><EFBFBD>*<2A>Automated system start-up sequence.
<EFBFBD><EFBFBD>*<2A>Graceful shutdown capability.
-----------------------------------------------------------------------------
6.2. Design
6.2.1. Determining necessary utilities
Loading the kernel without manually typing parameters is easy to do if we
read the grub info page. According to the section entitled "configuration"
all of the commands used for booting can be put in a file called menu.lst and
placed in the /boot/grub directory.
Note Be sure to type the menu.lst filename correctly with a lowercase L after
the dot and not a number one.
To automate system start-up we will need an init daemon. We know this because
the Bootdisk-HOWTO and From-Powerup-To-BASH-Prompt-HOWTO both make mention of
init as the first program to start after the kernel loads. The latter HOWTO
also goes into some detail about the /etc/inittab file and the organization
of startup scripts. This could be helpful since FHS, the blueprint we have
used so far, makes no recommendation for init scripts.
We will also need to find the shutdown command to fulfill the second goal of
graceful shutdown capability.
-----------------------------------------------------------------------------
6.2.2. Obtaining source code
Searching the Linux Software Map on Ibiblio for the keyword "init" gives a
large number of results. From reading the From-Powerup-To-BASH-Prompt-HOWTO
however, we know that most Linux systems use a System V style init daemon.
Narrowing the search with the additional key phrase of "System V" gives much
better results. The sysvinit package contains init, shutdown, halt and reboot
which is everything we need. The version listed in the LSM entry looks to be
pretty old, but there is a primary-site URL that will probably lead to the
latest version.
-----------------------------------------------------------------------------
6.2.3. Checking dependencies
The manpage for init mentions a FIFO called /dev/initctl that is required for
init to communicate with other programs in the sysvinit package. We will have
to create this file for init to function properly.
-----------------------------------------------------------------------------
6.2.4. Designing a simple GRUB configuration file.
Using a GRUB configuration file is slightly more complex than specifying the
bootloader commands manually. There are directives for features like menus,
default selections and timeouts that need to be specified in the
configuration file as well as the familiar kernel loading command. The info
page for GRUB gives much of the necessary information. We may also be able to
use the GRUB configuration file on the development system as a template.
However, there is some inconsistency between vendors as to the name and
location of the file. Regardless of what the path is on the development
system it should be /boot/grub/menu.lst on the Pocket Linux System.
-----------------------------------------------------------------------------
6.2.5. Outlining start-up scripts
Many of the popular GNU/Linux distributions use System V style init scripts.
Since we are using a "sysvinit" daemon it makes sense to use System V style
scripts as well. The following documents all touch upon the System V style
init scripts in some way and will serve as references when building the
scripts for this project:
<EFBFBD><EFBFBD>*<2A>The Debian Policy Manual -- available online at [http://www.debian.org/
doc/debian-policy] http://www.debian.org/doc/debian-policy.
<EFBFBD><EFBFBD>*<2A>The Linux Standard Base specification -- downloadable in many formats
from [http://www.linuxbase.org/spec/index.shtml] http://www.linuxbase.org
/spec/index.shtml.
<EFBFBD><EFBFBD>*<2A>Essential System Administration, 3rd Edition by Aeleen Frisch --
available at libraries, bookstores or directly from O'Reilly Publishing
at [http://www.oreilly.com/] http://www.oreilly.com/.
After glancing at one or two of the above references we should have a pretty
good idea of how the System V style system initialization process works. We
should also know what it takes to create System V style init scripts for the
Pocket Linux project. Below is a brief list of what needs to be done:
<EFBFBD><EFBFBD>*<2A>Create an inittab file to call an rc script with a numerical argument
giving the runlevel.
<EFBFBD><EFBFBD>*<2A>Write an rc script that uses the runlevel argument to execute the
appropriate "K" and "S" scripts.
<EFBFBD><EFBFBD>*<2A>Modify the previously built local_fs script to take start and stop
arguments.
<EFBFBD><EFBFBD>*<2A>Create new scripts for shutdown and reboot.
<EFBFBD><EFBFBD>*<2A>Set up /etc/rcN.d directories and links to scripts in /etc/init.d.
As always, the BASH(1) manpage and the Advanced BASH Scripting Guide are very
helpful for writing and understanding shell scripts.
-----------------------------------------------------------------------------
6.3. Construction
There is a lot of typing to do in this section because of all of the start-up
scripts that need to be created. Using a mouse to copy the text from this
guide and paste it into a text editor can be a great time saving tool.
-----------------------------------------------------------------------------
6.3.1. Create a GRUB configuration file
Insert and mount the floppy labeled "boot disk".
bash# mount /dev/fd0 /mnt
bash# cd /mnt/boot/grub
Use your favorite text editor to create the following file and save it as /
mnt/boot/grub/menu.lst:
default 0
timeout 3
title Pocket Linux Boot Disk
kernel (fd0)/boot/vmlinuz root=/dev/fd0 load_ramdisk=1 prompt_ramdisk=1
-----------------------------------------------------------------------------
6.3.2. Install sysvinit utilities
Download the latest sysvinit source from [ftp://ftp.cistron.nl/pub/people/
miquels/software/] ftp://ftp.cistron.nl/pub/people/miquels/software/
bash# cd /usr/src/sysvinit-2.85/src
bash# make CC="gcc -mcpu=i386"
bash# cp halt init shutdown ~/staging/sbin
bash# ln -s halt ~/staging/sbin/reboot
bash# ln -s init ~/staging/sbin/telinit
bash# mknod ~/staging/dev/initctl p
Note In the interest of speed we are skipping the steps for checking
libraries and stripping binaries. The library requirements for sysvinit
are very basic and the Makefile is configured to automatically strip the
binaries.
-----------------------------------------------------------------------------
6.3.3. Create /etc/inittab file
Use a text editor to create the following file and save it as ~/staging/etc/
inittab
# /etc/inittab - init daemon configuration file
#
# Default runlevel
id:1:initdefault:
#
# System initialization
si:S:sysinit:/etc/init.d/rc S
#
# Runlevel scripts
r0:0:wait:/etc/init.d/rc 0
r1:1:respawn:/bin/sh
r2:2:wait:/etc/init.d/rc 2
r3:3:wait:/etc/init.d/rc 3
r4:4:wait:/etc/init.d/rc 4
r5:5:wait:/etc/init.d/rc 5
r6:6:wait:/etc/init.d/rc 6
#
# end of /etc/inittab
-----------------------------------------------------------------------------
6.3.4. Create /etc/init.d/rc script
Use a text editor to create the following file and save it as ~/staging/etc/
init.d/rc
#!/bin/sh
#
# /etc/init.d/rc - runlevel change script
#
PATH=/sbin:/bin
SCRIPT_DIR="/etc/rc$1.d"
#
# Check that the rcN.d directory really exists.
if [ -d $SCRIPT_DIR ]; then
#
# Execute the kill scripts first.
for SCRIPT in $SCRIPT_DIR/K*; do
if [ -x $SCRIPT ]; then
$SCRIPT stop;
fi;
done;
#
# Do the Start scripts last.
for SCRIPT in $SCRIPT_DIR/S*; do
if [ -x $SCRIPT ]; then
$SCRIPT start;
fi;
done;
fi
#
# end of /etc/init.d/rc
Make the file executable.
bash# chmod +x ~/staging/etc/init.d/rc
-----------------------------------------------------------------------------
6.3.5. Modify /etc/init.d/local_fs script
A case statement is added to allow the script to either mount or unmount
local filesystems depending on the command-line argument given. The original
script is contained inside the "start" portion of the case statement. The
"stop" portion is new.
#!/bin/sh
#
# local_fs - check and mount local filesystems
#
PATH=/sbin:/bin ; export PATH
case $1 in
start)
echo "Checking local filesystem integrity."
fsck -ATCp
if [ $? -gt 1 ]; then
echo "Filesystem errors still exist! Manual intervention required."
/bin/sh
else
echo "Remounting / as read-write."
mount -n -o remount,rw /
echo -n > /etc/mtab
mount -f -o remount,rw /
echo "Mounting local filesystems."
mount -a -t nonfs,smbfs
fi
;;
stop)
echo "Unmounting local filesystems."
umount -a -r
;;
*)
echo "usage: $0 start|stop";
;;
esac
#
# end of local_fs
-----------------------------------------------------------------------------
6.3.6. Create a hostname script
Use a text editor to create the following script and save it as ~/staging/etc
/init.d/hostname
#!/bin/sh
#
# hostname - set the system name to the name stored in /etc/hostname
#
PATH=/sbin:/bin ; export PATH
echo "Setting hostname."
if [ -f /etc/hostname ]; then
hostname $(cat /etc/hostname)
else
hostname gnu-linux
fi
#
# end of hostname
-----------------------------------------------------------------------------
6.3.7. Create halt & reboot scripts
Use a text editor to create ~/staging/etc/init.d/halt as shown below.
#!/bin/sh
#
# halt - halt the system
#
PATH=/sbin:/bin ; export PATH
echo "Initiating system halt."
halt
#
# end of /etc/init.d/halt
Create the following script and save it as ~/staging/etc/init.d/reboot
#!/bin/sh
#
# reboot - reboot the system
#
PATH=/sbin:/bin ; export PATH
echo "Initiating system reboot."
reboot
#
# end of /etc/init.d/reboot
Flag all script files as executable.
bash# chmod +x ~/staging/etc/init.d/*
-----------------------------------------------------------------------------
6.3.8. Create rcN.d directories and links
bash# cd ~/staging/etc
bash# mkdir rc0.d rc1.d rc2.d rc3.d rc4.d rc5.d rc6.d rcS.d
bash# cd ~/staging/etc/rcS.d
bash# ln -s ../init.d/local_fs S20local_fs
bash# ln -s ../init.d/hostname S30hostname
bash# cd ~/staging/etc/rc0.d
bash# ln -s ../init.d/local_fs K10local_fs
bash# ln -s ../init.d/halt K90halt
bash# cd ~/staging/etc/rc6.d
bash# ln -s ../init.d/local_fs K10local_fs
bash# ln -s ../init.d/reboot K90reboot
-----------------------------------------------------------------------------
6.3.9. Create the root disk image
bash# cd /
bash# dd if=/dev/zero of=/dev/ram7 bs=1k count=4096
bash# mke2fs -m0 /dev/ram7 4096
bash# mount /dev/ram7 /mnt
bash# cp -dpR ~/staging/* /mnt
bash# umount /dev/ram7
bash# dd if=/dev/ram7 of=~/phase5-image bs=1k
bash# gzip -9 ~/phase5-image
-----------------------------------------------------------------------------
6.3.10. Copy the image to diskette
Insert the diskette labeled "root disk" into drive fd0.
bash# dd if=~/phase5-image.gz of=/dev/fd0 bs=1k
-----------------------------------------------------------------------------
6.4. Implementation
6.4.1. System Startup
Boot the PC using the floppy labeled "boot disk". Place the recently created
root disk in fd0 when prompted. The output should resemble the example below:
GNU GRUB version 0.95
Uncompressing Linux... Ok, booting kernel.
..
.. [various kernel messages]
..
VFS: Insert root floppy to be loaded into RAM disk and press ENTER
RAMDISK: Compressed image found at block 0
VFS: Mounted root (ext2 filesystem) readonly.
Freeing unused kernel memory: 178k freed
Checking local filesystem integrity.
/dev/ram0: clean 105/1024 files 2842/4096 blocks
Remounting / as read-write.
Mounting local filesystems.
Setting the hostname.
INIT: Entering runlevel: 1
# _
-----------------------------------------------------------------------------
6.4.2. Verify success of startup scripts
Use the mount command to check that local filesystems are mounted as
read-write. The output should look like the example below.
bash# mount
/dev/root on / type ext2 (rw)
proc on /proc type proc (rw)
Check the hostname.
bash# uname -n
gnu-linux
-----------------------------------------------------------------------------
6.4.3. System shutdown
Bring the system down gracefully with the shutdown command.
bash# shutdown -h now
We should see the following output from init and the shutdown scripts:
INIT: Switching to runlevel: 0
INIT: Sending processes the TERM signal
Terminated
INIT: Sending processes the KILL signal
Unmounting local filesystems.
Initiating system halt.
System halted.
-----------------------------------------------------------------------------
Chapter 7. Enabling Multiple Users
7.1. Analysis
Up to now the system has been operating in single-user mode. There is no
login process and anyone who boots the system goes straight into a shell with
root privileges. Obviously, this is not the normal operating mode for most
GNU/Linux distributions. Most systems feature multi-user capability where
many users can access the system simultaneously with different privilege
levels. These multi-user systems also support virtual consoles so that the
keyboard and video display can be multiplexed between several terminal
sessions. So in this phase we would like to add the following enhancements to
the system:
<EFBFBD><EFBFBD>*<2A>Enable multi-user capability.
<EFBFBD><EFBFBD>*<2A>Create multiple, virtual consoles.
-----------------------------------------------------------------------------
7.2. Design
7.2.1. The login process
The From-Powerup-To-BASH-Prompt-HOWTO does a good job of outlining the steps
in the login process. Basically it works like this.
1. The init daemon starts a getty process on the terminal.
2. The getty program displays the contents of /etc/issue and prompts for a
user name.
3. When the user name is entered, control is handed off to the login
program.
4. The login program asks for a password and verifies the credentials using
/etc/passwd, /etc/group and possibly /etc/shadow.
5. If everything is okay the user's shell is started.
-----------------------------------------------------------------------------
7.2.2. Obtaining source code
The getty and login programs were already installed as part of the util-linux
package so there is no need to download any new source code.
-----------------------------------------------------------------------------
7.2.3. Creating support files
7.2.3.1. Device nodes
Details about virtual console device files can be found in the Linux kernel
source code file called devices.txt in the Documentation directory. We will
need to create tty1 through tty6 for each of the virtual consoles as well as
tty0 and tty to represent the current virtual console.
-----------------------------------------------------------------------------
7.2.3.2. /etc/issue
The /etc/issue file is pretty easy to construct. It can contain any text we
want displayed on the screen prior to the login prompt. It could be something
friendly like "Welcome to Pocket Linux", something menacing like "Authorized
users only!" or something informational like "Connected to tty1 at 9600bps".
The agetty(8) manpage explains how to display information like tty line and
baud rate using escape codes.
-----------------------------------------------------------------------------
7.2.3.3. /etc/passwd
The format of /etc/passwd can be obtained by reading the passwd(5) manpage.
We can easily create a user account by adding a line like "root::0:0:
superuser:/root:/bin/sh" to the file.
Maintaining passwords will be somewhat challenging because of the system
being loaded into ramdisk. Any changes to /etc/passwd will be lost when the
system is shutdown. So to make things easy, we will create all users with
null passwords.
-----------------------------------------------------------------------------
7.2.3.4. /etc/group
The structure of /etc/group is available from the group(5) manpage. A line of
"root::0:root" would define a group called "root" with no password, a group
id of zero and the user root assigned to it as the only member.
-----------------------------------------------------------------------------
7.2.3.5. Conventions
User and group names and id's are generally not chosen at random. Most Linux
systems have very similar looking /etc/passwd and /etc/group files.
Definitions for commonly used user id and group id assignments may be found
in one of several places:
<EFBFBD><EFBFBD>*<2A>The /etc/passwd and /etc/group files on any popular GNU/Linux
distribution.
<EFBFBD><EFBFBD>*<2A>The Debian Policy Manual -- available online at [http://www.debian.org/
doc/debian-policy] http://www.debian.org/doc/debian-policy.
<EFBFBD><EFBFBD>*<2A>The Linux Standard Base specification -- downloadable in many formats
from [http://www.linuxbase.org/spec/index.shtml] http://www.linuxbase.org
/spec/index.shtml.
<EFBFBD><EFBFBD>*<2A>Essential System Administration, 3rd Edition by Aeleen Frisch --
available at libraries, bookstores or directly from O'Reilly Publishing
at [http://www.oreilly.com/] http://www.oreilly.com/.
-----------------------------------------------------------------------------
7.2.4. Dependencies
Running ldd on the login program from util-linux will reveal that it is
linked to the libraries libcrypt.so.1, libc.so.6 and ld-linux.so.2. In
addition to these libraries there is another, unseen dependency on
libnss_files.so.2 and the configuration file /etc/nsswitch.conf.
The name service switch library libnss_files.so.2 and nsswitch.conf are
required for libc.so.6, and consequently the login program, to access the /
etc/passwd file. Without libnss and its configuration file, all logins will
mysteriously fail. More information about glibc's use of the name service
switch libraries can be found at [http://www.gnu.org/software/libc/manual/
html_node/Name-Service-Switch.html] http://www.gnu.org/software/libc/manual/
html_node/Name-Service-Switch.html.
-----------------------------------------------------------------------------
7.2.5. Assigning ownership and permissions
Previously, with the single user system, there was no need to worry about
permissions when installing directories, files and device nodes. The shell
was effectively operating as root, so everything was accessible. Things
become more complex with the addition of multiple user capability. Now we
need to make sure that every user has access to what they need and at the
same time gets blocked from what they do not need.
A good guideline for assigning ownership and permissions would be to give the
minimum level of access required. Take the /bin directory as an example. The
Filesystem Hierarchy (FHS) document says, "/bin contains commands that may be
used by both the system administrator and by users". From that statement we
can infer that /bin should have read and execute permission for everyone. On
the other hand, the /boot directory contains files for the boot loader.
Chances are good that regular users will not need to access anything in the /
boot directory. So the minimum level of access would be read permission for
the root user and other administrators who are members of the root group.
Normal users would have no permissions assigned on the /boot directory.
Most of the time we can assign similar permissions to all the commands in a
directory, but there are some programs that prove to be exceptions to the
rule. The su command is a good example. Other commands in the /bin directory
have a minimum requirement of read and execute, but the su command needs to
be setuid root in order to run correctly. Since it is a setuid binary, it
might not be a good idea to allow just anyone to run it. Ownership of 0:0
(root user, root group) and permissions of rwsr-x--- (octal 4750) would be a
good fit for su.
The same logic can be applied to other directories and files in the root
filesystem using the following steps:
1. Assign ownership to the root user and root group.
2. Set the most restrictive permissions possible.
3. Adjust ownership and permissions on an "as needed" basis.
-----------------------------------------------------------------------------
7.3. Construction
7.3.1. Verify presence of getty and login
bash# ls ~/staging/sbin/getty
bash# ls ~/staging/bin/login
-----------------------------------------------------------------------------
7.3.2. Modify inittab for multi-user mode
Modify ~/staging/etc/inittab by changing the default runlevel and adding
getty entries as shown below.
# /etc/inittab - init daemon configuration file
#
# Default runlevel
id:2:initdefault:
#
# System initialization
si:S:sysinit:/etc/init.d/rc S
#
# Runlevel scripts
r0:0:wait:/etc/init.d/rc 0
r1:1:respawn:/bin/sh
r2:2:wait:/etc/init.d/rc 2
r3:3:wait:/etc/init.d/rc 3
r4:4:wait:/etc/init.d/rc 4
r5:5:wait:/etc/init.d/rc 5
r6:6:wait:/etc/init.d/rc 6
#
# Spawn virtual terminals
1:235:respawn:/sbin/getty 38400 tty1 linux
2:235:respawn:/sbin/getty 38400 tty2 linux
3:235:respawn:/sbin/getty 38400 tty3 linux
4:235:respawn:/sbin/getty 38400 tty4 linux
5:235:respawn:/sbin/getty 38400 tty5 linux
6:2345:respawn:/sbin/getty 38400 tty6 linux
#
# end of /etc/inittab
-----------------------------------------------------------------------------
7.3.3. Create tty devices
bash# cd ~/staging/dev
bash# mknod ~/staging/dev/tty0 c 4 0
bash# mknod ~/staging/dev/tty1 c 4 1
bash# mknod ~/staging/dev/tty2 c 4 2
bash# mknod ~/staging/dev/tty3 c 4 3
bash# mknod ~/staging/dev/tty4 c 4 4
bash# mknod ~/staging/dev/tty5 c 4 5
bash# mknod ~/staging/dev/tty6 c 4 6
bash# mknod ~/staging/dev/tty c 5 0
-----------------------------------------------------------------------------
7.3.4. Create support files in /etc
7.3.4.1. /etc/issue
Create the file ~/staging/etc/issue using the example below or design a
customized message.
Connected to \l at \b bps.
Be sure that "\l" is a lowercase letter L and not the number one.
-----------------------------------------------------------------------------
7.3.4.2. /etc/passwd
Use a text editor to create a minimal passwd file conforming to the Linux
Standards Base (LSB) document. Save the file as ~/staging/etc/passwd
root::0:0:Super User:/root:/bin/sh
bin:x:1:1:Legacy UID:/bin:/bin/false
daemon:x:2:2:Legacy UID:/sbin:/bin/false
-----------------------------------------------------------------------------
7.3.4.3. /etc/group
Use a text editor to create an LSB conforming group file and save it as ~/
staging/etc/group
root::0:root
bin:x:1:root,bin,daemon
daemon:x:2:root,bin,daemon
-----------------------------------------------------------------------------
7.3.4.4. /etc/nsswitch.conf
Create the following file and save it as ~/staging/etc/nsswitch.conf
passwd: files
group: files
-----------------------------------------------------------------------------
7.3.5. Copy required libraries
bash# cp /lib/libnss_files.so.2 ~/staging/lib
bash# strip --strip-unneeded ~/staging/lib/*
-----------------------------------------------------------------------------
7.3.6. Set directory and file permissions
Set minimal privileges on all files and directories under ~/staging.
Everything is owned by the root user and the root group. Permissions are
read-write for the owner and read-only for the group. Exceptions to the
blanket permissions are handled case by case.
bash# cd ~/staging
bash# chown -R 0:0 ~/staging/*
bash# chmod -R 640 ~/staging/*
Set execute permission on all directories. (Note the capital "X")
bash# chmod -R +X ~/staging/*
Files in /bin are read and execute for all, but su is an exception.
bash# chmod 755 ~/staging/bin/*
bash# chmod 4750 ~/staging/bin/su
Files in /dev have various permissions. Disk devices should be accessible to
administrators only. Other files like /dev/null should have full privileges
granted to everyone.
bash# chmod 660 ~/staging/dev/fd0 dev/ram0
bash# chmod 666 ~/staging/dev/null
bash# chmod 622 ~/staging/dev/console
bash# chmod 600 ~/staging/dev/initctl
bash# chmod 622 ~/staging/dev/tty
bash# chmod 622 ~/staging/dev/tty?
The passwd and group files must be world readable.
bash# chmod 644 ~/staging/etc/passwd
bash# chmod 644 ~/staging/etc/group
The scripts in /etc/init.d are read and execute for administrators.
bash# chmod 750 ~/staging/etc/init.d/*
Libraries need read and execute permissions for everyone.
bash# chmod 755 ~/staging/lib/*
Only root should have access to the /root directory.
bash# chmod 700 ~/staging/root
Make files in /sbin read and execute for administrators.
bash# chmod 750 ~/staging/sbin/*
Temp should be read-write for all with the sticky bit set.
bash# chmod 1777 ~/staging/tmp
-----------------------------------------------------------------------------
7.3.7. Create the root disk image
bash# cd /
bash# dd if=/dev/zero of=/dev/ram7 bs=1k count=4096
bash# mke2fs -m0 /dev/ram7 4096
bash# mount /dev/ram7 /mnt
bash# cp -dpR ~/staging/* /mnt
bash# umount /dev/ram7
bash# dd if=/dev/ram7 of=~/phase6-image bs=1k count=4096
bash# gzip -9 ~/phase6-image
-----------------------------------------------------------------------------
7.3.8. Copy the image to diskette
Insert the diskette labeled "root disk" into drive fd0.
bash# dd if=~/phase6-image.gz of=/dev/fd0 bs=1k
-----------------------------------------------------------------------------
7.4. Implementation
7.4.1. System Startup
If everything goes well, the virtual console display should look similar to
the following example:
Connected to tty1 at 38400 bps.
gnu-linux login:
-----------------------------------------------------------------------------
7.4.2. Add a new user to the system
Log in as root.
Create a new, unprivileged user and new group by appending a line to the /etc
/passwd and /etc/group files, respectively. Be sure to use a double
greater-than (>>) to avoid accidentally overwriting the files.
bash# echo "floyd::501:500:User:/home/floyd:/bin/sh" >>/etc/passwd
bash# echo "users::500:" >>/etc/group
bash# mkdir /home/floyd
bash# chown floyd.users /home/floyd
bash# chmod 700 /home/floyd
-----------------------------------------------------------------------------
7.4.3. Test the new user's ability to use the system
Switch to virtual terminal tty2 by pressing ALT+F2.
Log in as floyd.
Try the following commands and verify that they work.
bash$ pwd
bash$ ls -l /
bash$ cat /etc/passwd
Try the following commands and verify that they do not work.
bash$ ls /root
bash$ /sbin/shutdown -h now
bash$ su -
-----------------------------------------------------------------------------
7.4.4. System shutdown
Switch back to tty1 where root is logged in.
bash# shutdown -h now
-----------------------------------------------------------------------------
Chapter 8. Filling in the Gaps
8.1. Analysis
The root disk has come a long way since its humble beginnings as a
statically-linked shell. It now shares many features with the popular,
ready-made distributions. For example it has:
<EFBFBD><EFBFBD>*<2A>Several common utilities like cat, ls and so on.
<EFBFBD><EFBFBD>*<2A>Startup scripts that automatically check and mount filesystems.
<EFBFBD><EFBFBD>*<2A>Graceful shutdown capability.
<EFBFBD><EFBFBD>*<2A>Support for multiple users and virtual terminals.
As a final test, we can put the root disk up against the Filesystem Hierarchy
Standard (FHS) requirements for the root filesystem. (We will ignore anything
in the /usr hierarchy because of space constraints.) Compared to FHS
requirement, the only files missing are a few commands in the /bin directory.
Specifically, the root disk lacks the following commands:
<EFBFBD><EFBFBD>*<2A>more
<EFBFBD><EFBFBD>*<2A>ps
<EFBFBD><EFBFBD>*<2A>sed
In addition to the required commands, it might be nice to include the "ed"
editor listed as an option by the FHS. It is not as robust as vi or emacs,
but it works and it should fit onto the tiny root filesystem.
So in order to finish up this phase of the project, we need to accomplish the
following goals:
<EFBFBD><EFBFBD>*<2A>Add the more, ps and sed commands.
<EFBFBD><EFBFBD>*<2A>Install the optional ed editor.
-----------------------------------------------------------------------------
8.2. Design
8.2.1. more
There is a more command that comes with util-linux, but it will not work for
this project. The reason is because of library dependencies and space
constraints. The util-linux supplied more needs either the libncurses or
libtermcap to work and there just is not enough space on the root disk floppy
to fit everything in. So, in order to have a more command we will have to get
creative.
The more command is used to display a file page by page. It's a little like
having a cat command that pauses every twenty-five lines. The basic logic is
outlined below.
<EFBFBD><EFBFBD>*<2A>Read one line of the file.
<EFBFBD><EFBFBD>*<2A>Display the line on the screen.
<EFBFBD><EFBFBD>*<2A>If 25 lines have been displayed, pause.
<EFBFBD><EFBFBD>*<2A>Loop and do it again.
Of course there are some details left out like what to do if the screen
dimensions are not what we anticipated, but overall it is a fair
representation of what more does. Given this simple program logic, it should
not be hard to put together a short shell script that emulates the basic
functionality of more. The BASH(1) manpage and Adv-BASH-Scripting-Guide will
serve as references.
-----------------------------------------------------------------------------
8.2.2. More device files
The more script will need access to device files that are not on the root
disk yet. Specifically more needs to have stdin, stdout and stderr, but while
we are at it we should check for any other missing /dev files. The Linux
Standard Base requires null, zero and tty to be present in the /dev
directory. Files for null and tty already exist from previous phases of the
project, but we still need /dev/zero. We can refer to devices.txt in the
Linux source code Documentation directory for major and minor numbers.
-----------------------------------------------------------------------------
8.2.3. ps, sed & ed
These three packages can be found by using the Internet resources we have
used before plus one new site. The "sed" and "ed" packages can be found at
the same place we found BASH, on the [ftp://ftp.gnu.org] GNU FTP server. The
procps package shows up in an Ibiblio LSM search, but it is an old version.
In order to find the latest version we can go to the Freshmeat website at
[http://freshmeat.net] http://freshmeat.net and search for "procps" in
projects.
Both "sed" and "ed" packages feature GNU's familiar configure script and are
therefore very easy to build. There is no configure script for "procps" but
this does not make things too difficult. We can just read the package's
README file to find out about how to set various configuration options. We
can use one of these options to avoid the complexity of using and installing
libproc. Setting SHARED=0 makes libproc an integrated part of ps rather than
a separate, shared library.
-----------------------------------------------------------------------------
8.3. Construction
8.3.1. Write a "more" script
Create the following script with a text editor and save it as ~/staging/bin/
more.sh
#!/bin/sh
#
# more.sh - emulates the basic functions of the "more" binary without
# requiring ncurses or termcap libraries.
#
# Assume input is coming from STDIN unless a valid file is given as
# a command-line argument.
if [ -f $1 ]; then
INPUT="$1"
else
INPUT="/dev/stdin"
fi
#
# Set IFS to newline only. See BASH(1) manpage for details on IFS.
IFS=$'\n'
#
# If terminal dimensions are not already set as shell variables, take
# a guess of 80x25.
if [ "$COLUMNS" = "" ]; then
let COLUMNS=80;
fi
if [ "$LINES" = "" ]; then
let LINES=25;
fi
#
# Initialize line counter variable
let LINE_COUNTER=$LINES
#
# Read the input file one line at a time and display on STDOUT until
# the page fills up. Display "Press <Enter>" message on STDERR and wait
# for keypress from STDERR. Continue until the end of the input file.
# Any input line greater than $COLUMNS characters in length is wrapped
# and counts as multiple lines.
#
while read -n $COLUMNS LINE_BUFFER; do
echo "$LINE_BUFFER"
let LINE_COUNTER=$LINE_COUNTER-1
if [ $LINE_COUNTER -le 1 ]; then
echo "Press <ENTER> for next page or <CTRL>+C to quit.">/dev/stderr
read</dev/stderr
let LINE_COUNTER=$LINES
fi
done<$INPUT
#
# end of more.sh
Create a symbolic link for more
bash# ln -s more.sh ~/staging/bin/more
-----------------------------------------------------------------------------
8.3.2. Create additional device files
bash# ln -s /proc/self/fd ~/staging/dev/fd
bash# ln -s fd/0 ~/staging/dev/stdin
bash# ln -s fd/1 ~/staging/dev/stdout
bash# ln -s fd/2 ~/staging/dev/stderr
bash# mknod -m644 ~/staging/dev/zero c 1 5
-----------------------------------------------------------------------------
8.3.3. Install ps
Get the latest procps source package from [http://procps.sourceforge.net/]
http://procps.sourceforge.net/
bash# cd /usr/src/procps-3.2.3
bash# make SHARED=0 CC="gcc -mcpu=i386"
bash# cd ps
bash# cp ps ~/staging/bin
-----------------------------------------------------------------------------
8.3.4. Install sed
Download GNU's sed from [ftp://ftp.gnu.org/gnu/sed/] ftp://ftp.gnu.org/gnu/
sed/
bash# cd /usr/src/sed-4.1.2
bash# export CC="gcc -mcpu=i386"
bash# ./configure --host=i386-pc-linux-gnu
bash# make
bash# cd sed
bash# cp sed ~/staging/bin
-----------------------------------------------------------------------------
8.3.5. Install ed
The ed package also comes from GNU at [ftp://ftp.gnu.org/gnu/ed/] ftp://
ftp.gnu.org/gnu/ed/
bash# cd /usr/src/ed-0.2
bash# ./configure --host=i386-pc-linux-gnu
bash# make
bash# cp ed ~/staging/bin
-----------------------------------------------------------------------------
8.3.6. Strip binaries to save space
bash# strip ~/staging/bin/*
-----------------------------------------------------------------------------
8.3.7. Ensure proper permissions
bash# chown 0:0 ~/staging/bin/*
bash# chmod -R 755 ~/staging/bin
bash# chmod 4750 ~/staging/bin/su
-----------------------------------------------------------------------------
8.3.8. Create the root disk image
bash# cd /
bash# dd if=/dev/zero of=/dev/ram7 bs=1k count=4096
bash# mke2fs -m0 /dev/ram7 4096
bash# mount /dev/ram7 /mnt
bash# cp -dpR ~/staging/* /mnt
bash# umount /dev/ram7
bash# dd if=/dev/ram7 of=~/phase7-image bs=1k
bash# gzip -9 ~/phase7-image
-----------------------------------------------------------------------------
8.3.9. Copy the image to diskette
Insert the diskette labeled "root disk" into drive fd0.
bash# dd if=~/phase7-image.gz of=/dev/fd0 bs=1k
-----------------------------------------------------------------------------
8.4. Implementation
8.4.1. System startup
Boot from the diskset in the usual way and log in as root.
-----------------------------------------------------------------------------
8.4.2. Test the "more" script
Display kernel messages by piping the output of dmesg to more.
bash# dmesg | more
Examine the local_fs script by using more with a command-line argument.
bash# more /etc/init.d/local_fs
-----------------------------------------------------------------------------
8.4.3. Use ps to show running processes
Display processes for the user currently logged in.
bash# ps
Display all available information about all running processes.
bash# ps -ef
-----------------------------------------------------------------------------
8.4.4. Run a simple sed script
Use sed to display an alternate version of /etc/passwd.
bash# sed -e "s/Legacy/Old School/" /etc/passwd
Verify that sed did not make the changes permanent.
bash# cat /etc/passwd
-----------------------------------------------------------------------------
8.4.5. Test the "ed" editor
Use ed to change properties on the "daemon" user.
bash# ed -p*
ed* r /etc/passwd
ed* %p
ed* /daemon/s/Legacy/Old School/
ed* %p
ed* w
ed* q
Verify that the changes are permanent (at least until the system is
restarted.)
bash# cat /etc/passwd
-----------------------------------------------------------------------------
8.4.6. System shutdown
Bring the system down gracefully with the shutdown command.
-----------------------------------------------------------------------------
Chapter 9. Project Wrap Up
9.1. Celebrating Accomplishments
As the Pocket Linux Project draws to a close we should take a moment to
celebrate all of our accomplishments. Some of the highlights are listed
below:
<EFBFBD><EFBFBD>*<2A>We have built a system, from source code only, that fully implements all
of the commands described in the Filesystem Hierarchy Standard
requirements for a root filesystem.
<EFBFBD><EFBFBD>*<2A>We have learned how to use Internet resources to locate and download the
source code needed to build a GNU/Linux system.
<EFBFBD><EFBFBD>*<2A>We have written basic system startup and shutdown scripts and configured
them to execute in the proper runlevels.
<EFBFBD><EFBFBD>*<2A>We have included support for multiple users on virtual consoles and
implemented permissions on system files.
<EFBFBD><EFBFBD>*<2A>But most importantly, we have learned some good design techniques and
project management skills that will enable us to tackle any future
projects with ease and confidence.
-----------------------------------------------------------------------------
9.2. Planning Next Steps
The Pocket Linux system is nearly overflowing, so there really is no more
room to expand the current root diskette to support any additional commands
and features. This leaves us with a few choices of where to go next. We can:
<EFBFBD><EFBFBD>*<2A>Find a way to expand the current system just enough to host a small
application. (For more information about hosting applications with Pocket
Linux, see Appendix A)
<EFBFBD><EFBFBD>*<2A>Remove multi-user capability and some of the less often used commands
from the root disk, replacing them with utilities like tar and gzip that
would be useful for a rescue/restore diskset.
<EFBFBD><EFBFBD>*<2A>Use the techniques we have learned to design and build an entire GNU/
Linux system and install it on a more spacious hard disk partition. (For
more infomation about building a larger system, check out the GNU/Linux
System Architect Toolkit at: [http://architect.sourceforge.net/] http://
architect.sourceforge.net/.)
Which ever path is chosen, we can move forward confidently, armed with the
knowledge we need to be successful in our endeavors.
-----------------------------------------------------------------------------
Appendix A. Hosting Applications
A.1. Analysis
An operating system by itself is not much fun. What makes an OS great is the
applications that can be run on top of it. Unfortunately, Pocket Linux
currently does not have much room for anything other than system programs.
Still, it would be nice to expand the system just enough to host some cool
applications. Obviously a full-blown X-Windows GUI is out of the question,
but running a small console based program should be within our reach.
Rather than doing a typical "hello world" program as an example, application
hosting will be demonstrated using a console based audio player called
mp3blaster. Building mp3blaster offers more technical challenge than "hello
world" and the finished product should be a lot more fun. However, it should
not be construed that a console-based jukebox is the only application for
Pocket Linux. On the contrary, after completing this phase the reader should
have the knowledge and tools to build almost any console-based program he or
she desires.
So what will it take to turn a pocket-sized GNU/Linux system into a
pocket-sized mp3 player? A few things are listed below.
<EFBFBD><EFBFBD>*<2A>Add support for audio hardware.
<EFBFBD><EFBFBD>*<2A>Create space for the mp3blaster program.
<EFBFBD><EFBFBD>*<2A>Provide a convenient way to access audio files.
-----------------------------------------------------------------------------
A.2. Design
A.2.1. Support for audio hardware
There is a vast proliferation of audio hardware on the market and each sound
card has its own particular configuration. For details on how to set up a
particular sound card we can turn to the Sound-HOWTO available from The Linux
Documentation Project. In a broader sense, however, we can treat a sound card
like any other piece of new hardware. To add new hardware to a GNU/Linux
system we will need configure the kernel to recognize it and configure /dev
files on the root disk to access it.
-----------------------------------------------------------------------------
A.2.1.1. Kernel support for audio
In order to support sound cards, a new kernel will have to be built. It is
very important that audio hardware support be configured as built-in, because
Pocket Linux is not set up to handle kernel modules.
-----------------------------------------------------------------------------
A.2.1.2. Root disk support for audio
Searching devices.txt for the keyword "sound" will list quite a few possible
audio devices, but usually only /dev/dsp and /dev/mixer are required to get
sound from a PC. These two files control the digital audio output and mixer
controls, respectively.
-----------------------------------------------------------------------------
A.2.2. Creating space for the program
Probably the easiest way to create more space for the mp3blaster program is
to mount an additional storage device. There are several choices for mount
points. So far /usr, /home and /opt are all empty directories and any one of
them could be used to mount a floppy, CD-ROM or additional compressed ramdisk
image. The /usr directory is a logical choice for a place to put an
application, but what about the choice of media? Mp3blaster and its required
libraries are too big to fit on a 1.44M floppy and burning a CD-ROM seems
like a lot of work for one little program. So given these constraints, the
best choice would be to put the program on a compressed floppy.
-----------------------------------------------------------------------------
A.2.2.1. Mounting additional compressed floppies
Mounting CDs and uncompressed diskettes is easy, but what about loading
compressed images from floppy into ramdisk? It will have to be done manually,
because automatic mounting of compressed floppies only works for the root
diskette. And using mount /dev/fd0 will not work because there is no
filesystem on the diskette, there are only the contents of a gzip file. The
actual filesystem is contained inside the gzip file. So how can we mount the
filesystem buried beneath the gzip file? This puzzle can be solved by
examining at the steps used to create the familiar compressed root disk
floppy.
1. A ramdisk is created, mounted and filled with files.
2. The ramdisk device is unmounted.
3. The contents of the ramdisk are dumped to an image file using dd.
4. The image file is compressed with gzip.
5. The compressed image file is written to floppy with dd.
If that is how the compressed image makes its way from ramdisk to compressed
floppy, then going from compressed floppy to ramdisk should be as simple as
running through the steps in reverse.
1. The compressed image file is read from floppy with dd.
2. The image file is uncompressed with gunzip.
3. The contents of the image file are dumped into ramdisk using dd.
4. The ramdisk device is mounted.
5. The files are available.
We can cut out the intermediate image file by using a pipe to combine dd and
gunzip like this: dd if=/dev/fd0 | gunzip -cq > /dev/ram1. Now the compressed
floppy goes straight into ramdisk, decompressing on the fly.
-----------------------------------------------------------------------------
A.2.2.2. Root disk support for additional ramdisks
We already have kernel support for ramdisks, because we are using a
compressed root disk, but we will need to create more ramdisks in /dev.
Typically the kernel supports eight ramdisks on /dev/ram0 through /dev/ram7
with ram0 being used for the rootdisk. The devices.txt file included in the
Linux source code documentation will be helpful for matching devices to their
major and minor numbers.
-----------------------------------------------------------------------------
A.2.3. Accessing audio files
The sample mp3 file that we will be using in our example is small enough to
fit on an uncompressed floppy disk so that there is no need to burn a CD.
However, serious music lovers may want to have the capability to mount a
custom CD-ROM full of tunes and that option will require support for
additional hardware.
-----------------------------------------------------------------------------
A.2.3.1. CD-ROM hardware support
Most modern CD-ROM drives will use IDE devices like /dev/hdc or /dev/hdd. To
support these CD-ROM drives we will have to configure IDE support in the
kernel and create the appropriate device files on the root disk.
-----------------------------------------------------------------------------
A.2.3.2. CD-ROM filesystem support
CD-ROMs have different filesystems than hard disks and floppies. Most CD
burning applications use a filesystem called ISO-9660 and have the capability
to support Joliet or Rockridge extensions. We will have to include support
for these filesystems in the kernel in order to mount CD-ROMs.
-----------------------------------------------------------------------------
A.2.4. Other required files
We will want to have all of mp3blaster's required libraries and other
supporting files available as part of the compressed /usr image so that
mp3blaster can run correctly. The familiar ldd command can be used to
determine which libraries mp3blaster requires. Any additional libraries can
be placed in /usr/lib. Even though some of the libraries may appear in /lib
on the development system, they can still go in /usr/lib on the Pocket Linux
system. The dynamic linker, ld-linux.so, is smart enough to look in both
places when loading libraries.
Because mp3blaster uses the curses (or ncurses) screen control library there
is one additional file we need. The curses library needs to know the
characteristics of the terminal it is controlling and it gets that
information from the terminfo database. The terminfo database consists of all
the files under the /usr/share/terminfo directory and is very large compared
to our available disk space. But, since Pocket Linux only supports the PC
console, we only have one terminal type to worry about and therefore need
only one file. The piece of the terminfo database we need is the file /usr/
share/terminfo/l/linux, because we are using a "Linux" terminal. For more
information about the subject of curses, see John Strang's book entitled
"Programming with Curses" available from O'Reilly publishing.
-----------------------------------------------------------------------------
A.2.5. Summary of tasks
Between sound cards, ramdisks, CD-ROMs and terminfo there is quite a bit to
keep track of. So let's take a moment to organize and summarize the tasks
necessary to make the pocket jukebox a reality.
<EFBFBD><EFBFBD>*<2A>Create a new kernel disk that includes built-in support for audio
hardware, IDE devices and CD-ROM filesystems.
<EFBFBD><EFBFBD>*<2A>Create the appropriate /dev files on the root disk to support audio
hardware, additional ramdisks and IDE CD-ROMs.
<EFBFBD><EFBFBD>*<2A>Install the gunzip utility to enable decompression of the usr image.
<EFBFBD><EFBFBD>*<2A>Create a startup script to load a compressed image from floppy into a
ramdisk and mount the ramdisk on /usr.
<EFBFBD><EFBFBD>*<2A>Create a compressed floppy that holds the mp3blaster program, its
required libraries and terminfo files.
-----------------------------------------------------------------------------
A.3. Construction
A.3.1. Create an enhanced boot disk
A.3.1.1. Build a new kernel
bash# cd /usr/src/linux
bash# make menuconfig
Be sure to configure support for the following:
<EFBFBD><EFBFBD>*<2A>386 processor
<EFBFBD><EFBFBD>*<2A>Floppy disk
<EFBFBD><EFBFBD>*<2A>RAM disk
<EFBFBD><EFBFBD>*<2A>Second extended (ext2) filesystem
<EFBFBD><EFBFBD>*<2A>Virtual console
<EFBFBD><EFBFBD>*<2A>Audio hardware
<EFBFBD><EFBFBD>*<2A>CD-ROM hardware
<EFBFBD><EFBFBD>*<2A>ISO-9660 and Joliet filesystems
bash# make dep
bash# make clean
bash# make bzImage
-----------------------------------------------------------------------------
A.3.1.2. Copy the kernel to diskette
Place the boot disk in drive fd0
bash# mount /dev/fd0 /mnt
bash# cp /usr/src/linux/arch/i386/boot/bzImage /mnt/boot/vmlinuz
-----------------------------------------------------------------------------
A.3.1.3. Unmount the boot disk
bash# cd /
bash# umount /mnt
-----------------------------------------------------------------------------
A.3.2. Create an enhanced root disk
A.3.2.1. Create additional device files
A.3.2.1.1. IDE CD-ROM
bash# mknod -m640 ~/staging/dev/hdc b 22 0
bash# mknod -m640 ~/staging/dev/hdd b 22 64
Optionally create additional IDE devices.
-----------------------------------------------------------------------------
A.3.2.1.2. Ramdisk
bash# mknod -m 640 ~/staging/dev/ram1 b 1 1
bash# mknod -m 640 ~/staging/dev/ram2 b 1 2
bash# mknod -m 640 ~/staging/dev/ram3 b 1 3
bash# mknod -m 640 ~/staging/dev/ram4 b 1 4
bash# mknod -m 640 ~/staging/dev/ram5 b 1 5
bash# mknod -m 640 ~/staging/dev/ram6 b 1 6
bash# mknod -m 640 ~/staging/dev/ram7 b 1 7
-----------------------------------------------------------------------------
A.3.2.1.3. Audio
bash# mknod -m664 ~/staging/dev/dsp c 14 3
bash# mknod -m664 ~/staging/dev/mixer c 14 0
-----------------------------------------------------------------------------
A.3.2.2. Install the gunzip binary
bash# cd /usr/src/gzip-1.2.4a
bash# export CC="gcc -mcpu=i386"
bash# ./configure --host=i386-pc-linux-gnu
bash# make
bash# strip gzip
bash# cp gzip ~/staging/bin
bash# ln -s gzip ~/staging/bin/gunzip
Don't forget to verify library requirements, check the ownership and check
permissions on the gzip binary.
-----------------------------------------------------------------------------
A.3.2.3. Write a startup script to mount a compressed floppy
Use a text editor to create the following script and save it as ~/staging/etc
/init.d/usr_image
#!/bin/sh
#
# usr_image - load compressed images from floppy into ramdisk and
# mount on /usr.
#
echo -n "Is there a compressed diskette to load for /usr [y/N]? "
read REPLY
if [ "$REPLY" = "y" ] || [ "$REPLY" = "Y" ]; then
echo -n "Please insert the /usr floppy into fd0 and press <ENTER>."
read REPLY
echo "Clearing /dev/ram1."
dd if=/dev/zero of=/dev/ram1 bs=1k count=4096
echo "Loading compressed image from /dev/fd0 into /dev/ram1..."
(dd if=/dev/fd0 bs=1k | gunzip -cq) >/dev/ram1 2>/dev/null
fsck -fp /dev/ram1
if [ $? -gt 1 ]; then
echo "Filesystem errors on /dev/ram1! Manual intervention required."
else
echo "Mounting /usr."
mount /dev/ram1 /usr
fi
fi
#
# end of usr_image
Configure the script to run right after root is mounted.
bash# ln -s ../init.d/usr_image ~/staging/etc/rcS.d/S21usr_image
-----------------------------------------------------------------------------
A.3.2.4. Create a compressed root disk
bash# cd /
bash# dd if=/dev/zero of=/dev/ram7 bs=1k count=4096
bash# mke2fs -m0 /dev/ram7
bash# mount /dev/ram7 /mnt
bash# cp -dpR ~/staging/* /mnt
bash# umount /dev/ram7
bash# dd if=/dev/ram7 of=~/phase8-image bs=1k
bash# gzip -9 ~/phase8-image
Insert the diskette labeled "root disk" into drive fd0.
bash# dd if=~/phase8-image.gz of=/dev/fd0 bs=1k
-----------------------------------------------------------------------------
A.3.3. Create a compressed /usr disk for mp3blaster
The compressed /usr diskette will be created in using the same process that
is used to create the compressed root disk. We will copy files to a staging
area, copy the staging area to ramdisk, compress the ramdisk and write it to
diskette.
-----------------------------------------------------------------------------
A.3.3.1. Create a staging area
bash# mkdir ~/usr-staging
bash# cd ~/usr-staging
bash# mkdir bin lib
bash# mkdir -p share/terminfo/l
-----------------------------------------------------------------------------
A.3.3.2. Install the mp3blaster program
Download the latest version of mp3blaster source code from its home at [http:
//www.stack.nl/~brama/mp3blaster/] http://www.stack.nl/~brama/mp3blaster/.
bash# cd ~/usr/src/mp3blaster-3.2.0
bash# ./configure
bash# make
bash# cp src/mp3blaster ~/usr-staging/bin
-----------------------------------------------------------------------------
A.3.3.3. Copy additional libraries and terminfo
Use ldd to find out which libraries are needed for mp3blaster.
Note The following is an example from the author's development system. It is
possible that different systems may yield slightly different results in
terms of library requirements.
bash# cd ~/usr-staging/lib
bash# ldd ~/usr-staging/bin/mp3blaster
bash# cp /usr/lib/ncurses.so.5.0 .
bash# cp /usr/lib/stdc++.so.3 .
bash# cp /lib/libm.so.6 .
bash# cp /usr/lib/libgcc_s.so.1 .
bash# cd ~/usr-staging/share/terminfo/l
bash# cp /usr/share/terminfo/l/linux .
-----------------------------------------------------------------------------
A.3.3.4. Make a compressed image and copy it to diskette
bash# cd /
bash# dd if=/dev/zero of=/dev/ram7 bs=1k count=4096
bash# mke2fs -m0 /dev/ram7
bash# mount /dev/ram7 /mnt
bash# cp -dpR ~/usr-staging/* /mnt
bash# umount /dev/ram7
bash# dd if=/dev/ram7 of=~/mp3blaster-image bs=1k
bash# gzip -9 ~/mp3blaster-image
Insert the diskette labeled "mp3blaster" into drive fd0.
bash# dd if=~/mp3blaster-image.gz of=/dev/fd0 bs=1k
-----------------------------------------------------------------------------
A.3.4. Create a data diskette for testing
Go to the Internet site [http://www.paul.sladen.org] http://
www.paul.sladen.org and download the mp3 file of Linus Torvalds pronouncing
"Linux." The direct link is: [http://www.paul.sladen.org/pronunciation/
torvalds-says-linux.mp3] http://www.paul.sladen.org/pronunciation/
torvalds-says-linux.mp3. Create a Second Extended (ext2) filesystem on a
floppy and copy the mp3 file onto the diskette.
-----------------------------------------------------------------------------
A.4. Implementation
A.4.1. System Startup
1. Boot from the kernel diskette.
2. Insert the root floppy when prompted.
3. When prompted for a /usr diskette, say 'Y'.
4. Insert the mp3blaster diskette and press Enter.
-----------------------------------------------------------------------------
A.4.2. Verify that the /usr diskette loaded properly
bash# mount
bash# ls -lR /usr
-----------------------------------------------------------------------------
A.4.3. Check the audio device initialization
bash# dmesg | more
If everything worked there should be a line or two indicating that the kernel
found the audio hardware. The example below shows how the kernel might report
a Yamaha integrated sound system.
ymfpci: YMF740C at 0xf4000000 IRQ 10
ac97_codec: AC97 Audio codec, id: 0x4144:0x5303 (Analog Devices AD1819)
-----------------------------------------------------------------------------
A.4.4. Test audio output
bash# echo "Garbage" > /dev/dsp
A short burst of static coming from the PC speakers indicates that sound is
working.
-----------------------------------------------------------------------------
A.4.5. Play a sample file
Insert the diskette containing the sample audio file.
mount /dev/fd0 /home
bash# /usr/bin/mp3blaster
Use mp3blaster to select and play the file /home/torvalds-says-linux.mp3. Use
mp3blaster's mixer controls to adjust the volume as needed.
-----------------------------------------------------------------------------
A.4.6. System shutdown
Bring the system down gracefully with the shutdown command.
-----------------------------------------------------------------------------
Appendix B. GNU Free Documentation License
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 59 Temple
Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted to copy
and distribute verbatim copies of this license document, but changing it
is not allowed.
-----------------------------------------------------------------------------
B.1. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to assure
everyone the effective freedom to copy and redistribute it, with or without
modifying it, either commercially or noncommercially. Secondarily, this
License preserves for the author and publisher a way to get credit for their
work, while not being considered responsible for modifications made by
others.
This License is a kind of "copyleft", which means that derivative works of
the document must themselves be free in the same sense. It complements the
GNU General Public License, which is a copyleft license designed for free
software.
We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free program
should come with manuals providing the same freedoms that the software does.
But this License is not limited to software manuals; it can be used for any
textual work, regardless of subject matter or whether it is published as a
printed book. We recommend this License principally for works whose purpose
is instruction or reference.
-----------------------------------------------------------------------------
B.2. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be distributed
under the terms of this License. Such a notice grants a world-wide,
royalty-free license, unlimited in duration, to use that work under the
conditions stated herein. The "Document", below, refers to any such manual or
work. Any member of the public is a licensee, and is addressed as "you". You
accept the license if you copy, modify or distribute the work in a way
requiring permission under copyright law.
A "Modified Version" of the Document means any work containing the Document
or a portion of it, either copied verbatim, or with modifications and/or
translated into another language.
A "Secondary Section" is a named appendix or a front-matter section of the
Document that deals exclusively with the relationship of the publishers or
authors of the Document to the Document's overall subject (or to related
matters) and contains nothing that could fall directly within that overall
subject. (Thus, if the Document is in part a textbook of mathematics, a
Secondary Section may not explain any mathematics.) The relationship could be
a matter of historical connection with the subject or with related matters,
or of legal, commercial, philosophical, ethical or political position
regarding them.
The "Invariant Sections" are certain Secondary Sections whose titles are
designated, as being those of Invariant Sections, in the notice that says
that the Document is released under this License. If a section does not fit
the above definition of Secondary then it is not allowed to be designated as
Invariant. The Document may contain zero Invariant Sections. If the Document
does not identify any Invariant Sections then there are none.
The "Cover Texts" are certain short passages of text that are listed, as
Front-Cover Texts or Back-Cover Texts, in the notice that says that the
Document is released under this License. A Front-Cover Text may be at most 5
words, and a Back-Cover Text may be at most 25 words.
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the general
public, that is suitable for revising the document straightforwardly with
generic text editors or (for images composed of pixels) generic paint
programs or (for drawings) some widely available drawing editor, and that is
suitable for input to text formatters or for automatic translation to a
variety of formats suitable for input to text formatters. A copy made in an
otherwise Transparent file format whose markup, or absence of markup, has
been arranged to thwart or discourage subsequent modification by readers is
not Transparent. An image format is not Transparent if used for any
substantial amount of text. A copy that is not "Transparent" is called
"Opaque".
Examples of suitable formats for Transparent copies include plain ASCII
without markup, Texinfo input format, LaTeX input format, SGML or XML using a
publicly available DTD, and standard-conforming simple HTML, PostScript or
PDF designed for human modification. Examples of transparent image formats
include PNG, XCF and JPG. Opaque formats include proprietary formats that can
be read and edited only by proprietary word processors, SGML or XML for which
the DTD and/or processing tools are not generally available, and the
machine-generated HTML, PostScript or PDF produced by some word processors
for output purposes only.
The "Title Page" means, for a printed book, the title page itself, plus such
following pages as are needed to hold, legibly, the material this License
requires to appear in the title page. For works in formats which do not have
any title page as such, "Title Page" means the text near the most prominent
appearance of the work's title, preceding the beginning of the body of the
text.
A section "Entitled XYZ" means a named subunit of the Document whose title
either is precisely XYZ or contains XYZ in parentheses following text that
translates XYZ in another language. (Here XYZ stands for a specific section
name mentioned below, such as "Acknowledgements", "Dedications",
"Endorsements", or "History".) To "Preserve the Title" of such a section when
you modify the Document means that it remains a section "Entitled XYZ"
according to this definition.
The Document may include Warranty Disclaimers next to the notice which states
that this License applies to the Document. These Warranty Disclaimers are
considered to be included by reference in this License, but only as regards
disclaiming warranties: any other implication that these Warranty Disclaimers
may have is void and has no effect on the meaning of this License.
-----------------------------------------------------------------------------
B.3. VERBATIM COPYING
You may copy and distribute the Document in any medium, either commercially
or noncommercially, provided that this License, the copyright notices, and
the license notice saying this License applies to the Document are reproduced
in all copies, and that you add no other conditions whatsoever to those of
this License. You may not use technical measures to obstruct or control the
reading or further copying of the copies you make or distribute. However, you
may accept compensation in exchange for copies. If you distribute a large
enough number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and you may
publicly display copies.
-----------------------------------------------------------------------------
B.4. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have printed
covers) of the Document, numbering more than 100, and the Document's license
notice requires Cover Texts, you must enclose the copies in covers that
carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the
front cover, and Back-Cover Texts on the back cover. Both covers must also
clearly and legibly identify you as the publisher of these copies. The front
cover must present the full title with all words of the title equally
prominent and visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve the
title of the Document and satisfy these conditions, can be treated as
verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you
should put the first ones listed (as many as fit reasonably) on the actual
cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more
than 100, you must either include a machine-readable Transparent copy along
with each Opaque copy, or state in or with each Opaque copy a
computer-network location from which the general network-using public has
access to download using public-standard network protocols a complete
Transparent copy of the Document, free of added material. If you use the
latter option, you must take reasonably prudent steps, when you begin
distribution of Opaque copies in quantity, to ensure that this Transparent
copy will remain thus accessible at the stated location until at least one
year after the last time you distribute an Opaque copy (directly or through
your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give them
a chance to provide you with an updated version of the Document.
-----------------------------------------------------------------------------
B.5. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the
conditions of sections 2 and 3 above, provided that you release the Modified
Version under precisely this License, with the Modified Version filling the
role of the Document, thus licensing distribution and modification of the
Modified Version to whoever possesses a copy of it. In addition, you must do
these things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title distinct from
that of the Document, and from those of previous versions (which should,
if there were any, be listed in the History section of the Document). You
may use the same title as a previous version if the original publisher of
that version gives permission.
B. List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified Version,
together with at least five of the principal authors of the Document (all
of its principal authors, if it has fewer than five), unless they release
you from this requirement.
C. State on the Title page the name of the publisher of the Modified
Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications adjacent to
the other copyright notices.
F. Include, immediately after the copyright notices, a license notice giving
the public permission to use the Modified Version under the terms of this
License, in the form shown in the Addendum below.
G. Preserve in that license notice the full lists of Invariant Sections and
required Cover Texts given in the Document's license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title, and add to
it an item stating at least the title, year, new authors, and publisher
of the Modified Version as given on the Title Page. If there is no
section Entitled "History" in the Document, create one stating the title,
year, authors, and publisher of the Document as given on its Title Page,
then add an item describing the Modified Version as stated in the
previous sentence.
J. Preserve the network location, if any, given in the Document for public
access to a Transparent copy of the Document, and likewise the network
locations given in the Document for previous versions it was based on.
These may be placed in the "History" section. You may omit a network
location for a work that was published at least four years before the
Document itself, or if the original publisher of the version it refers to
gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications", Preserve
the Title of the section, and preserve in the section all the substance
and tone of each of the contributor acknowledgements and/or dedications
given therein.
L. Preserve all the Invariant Sections of the Document, unaltered in their
text and in their titles. Section numbers or the equivalent are not
considered part of the section titles.
M. Delete any section Entitled "Endorsements". Such a section may not be
included in the Modified Version.
N. Do not retitle any existing section to be Entitled "Endorsements" or to
conflict in title with any Invariant Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that
qualify as Secondary Sections and contain no material copied from the
Document, you may at your option designate some or all of these sections as
invariant. To do this, add their titles to the list of Invariant Sections in
the Modified Version's license notice. These titles must be distinct from any
other section titles.
You may add a section Entitled "Endorsements", provided it contains nothing
but endorsements of your Modified Version by various parties--for example,
statements of peer review or that the text has been approved by an
organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list of
Cover Texts in the Modified Version. Only one passage of Front-Cover Text and
one of Back-Cover Text may be added by (or through arrangements made by) any
one entity. If the Document already includes a cover text for the same cover,
previously added by you or by arrangement made by the same entity you are
acting on behalf of, you may not add another; but you may replace the old
one, on explicit permission from the previous publisher that added the old
one.
The author(s) and publisher(s) of the Document do not by this License give
permission to use their names for publicity for or to assert or imply
endorsement of any Modified Version.
-----------------------------------------------------------------------------
B.6. COMBINING DOCUMENTS
You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified versions,
provided that you include in the combination all of the Invariant Sections of
all of the original documents, unmodified, and list them all as Invariant
Sections of your combined work in its license notice, and that you preserve
all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple
identical Invariant Sections may be replaced with a single copy. If there are
multiple Invariant Sections with the same name but different contents, make
the title of each such section unique by adding at the end of it, in
parentheses, the name of the original author or publisher of that section if
known, or else a unique number. Make the same adjustment to the section
titles in the list of Invariant Sections in the license notice of the
combined work.
In the combination, you must combine any sections Entitled "History" in the
various original documents, forming one section Entitled "History"; likewise
combine any sections Entitled "Acknowledgements", and any sections Entitled
"Dedications". You must delete all sections Entitled "Endorsements".
-----------------------------------------------------------------------------
B.7. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in the
collection, provided that you follow the rules of this License for verbatim
copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it
individually under this License, provided you insert a copy of this License
into the extracted document, and follow this License in all other respects
regarding verbatim copying of that document.
-----------------------------------------------------------------------------
B.8. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and
independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright resulting from
the compilation is not used to limit the legal rights of the compilation's
users beyond what the individual works permit. When the Document is included
in an aggregate, this License does not apply to the other works in the
aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of
the Document, then if the Document is less than one half of the entire
aggregate, the Document's Cover Texts may be placed on covers that bracket
the Document within the aggregate, or the electronic equivalent of covers if
the Document is in electronic form. Otherwise they must appear on printed
covers that bracket the whole aggregate.
-----------------------------------------------------------------------------
B.9. TRANSLATION
Translation is considered a kind of modification, so you may distribute
translations of the Document under the terms of section 4. Replacing
Invariant Sections with translations requires special permission from their
copyright holders, but you may include translations of some or all Invariant
Sections in addition to the original versions of these Invariant Sections.
You may include a translation of this License, and all the license notices in
the Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions of
those notices and disclaimers. In case of a disagreement between the
translation and the original version of this License or a notice or
disclaimer, the original version will prevail.
If a section in the Document is Entitled "Acknowledgements", "Dedications",
or "History", the requirement (section 4) to Preserve its Title (section 1)
will typically require changing the actual title.
-----------------------------------------------------------------------------
B.10. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as
expressly provided for under this License. Any other attempt to copy, modify,
sublicense or distribute the Document is void, and will automatically
terminate your rights under this License. However, parties who have received
copies, or rights, from you under this License will not have their licenses
terminated so long as such parties remain in full compliance.
-----------------------------------------------------------------------------
B.11. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU
Free Documentation License from time to time. Such new versions will be
similar in spirit to the present version, but may differ in detail to address
new problems or concerns. See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the
Document specifies that a particular numbered version of this License "or any
later version" applies to it, you have the option of following the terms and
conditions either of that specified version or of any later version that has
been published (not as a draft) by the Free Software Foundation. If the
Document does not specify a version number of this License, you may choose
any version ever published (not as a draft) by the Free Software Foundation.
-----------------------------------------------------------------------------
B.12. ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the
License in the document and put the following copyright and license notices
just after the title page:
Copyright (c) YEAR YOUR NAME. Permission is granted to copy, distribute
and/or modify this document under the terms of the GNU Free Documentation
License, Version 1.2 or any later version published by the Free Software
Foundation; with no Invariant Sections, no Front-Cover Texts, and no
Back-Cover Texts. A copy of the license is included in the section
entitled "GNU Free Documentation License".
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover
Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination
of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend
releasing these examples in parallel under your choice of free software
license, such as the GNU General Public License, to permit their use in free
software.
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