Carbs Linux User Manual

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Carbs Linux User Manual

This is the full documentation of Carbs Linux, from the details of the distribution, installation, to the package manager. It is not yet complete.

This documentation is also available in the distribution by the carbs-docs package, which can be read by either running info carbslinux or reading /usr/share/doc/carbslinux.txt with your favorite pager. You can install either the info or texinfo for doing the first.


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1 Installation

These are the step-by-step instructions for installing Carbs Linux. It can be acquired as plain-text to be viewed offline with a pager from https://carbslinux.org/install.txt.

curl -sL https://carbslinux.org/install.txt | less

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1.1 Preparing Environment

To install Carbs Linux, you will need a Live Linux ISO. For that purpose, you can obtain a Gentoo or Void Linux live image. You can follow their instructions to boot and setup your network.

You will need the following programs in order to install Carbs Linux:

Rest of these instructions will assume that you have set all of these up, and will continue on that point.


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1.1.1 Download

First, we need to download the rootfs tarball. You can do the following in order to obtain the rootfs. If you are using an i686 machine, replace the ‘x86_64’ with ‘i686’. We are setting this in a URL variable so that we don’t have to write it every time.

URL=https://dl.carbslinux.org/releases/x86_64
wget $URL/carbs-rootfs.tar.xz.sha256
sha256sum -c carbs-rootfs.tar.xz.sha256

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1.1.2 Signature verification

It is highly recommended to verify the signature of the tarball. You will need the OpenBSD tool ‘signify(1)’ for this. Many distributions provide a package for it, if you are using a Carbs Linux host, you can also install the package ‘otools’ which provides ‘signify’. Download the signature first.

wget $URL/carbs-rootfs.tar.xz.sig

The signature file should say something similar to

untrusted comment: verify with carbslinux-2021.04.pub
RWTBBPDVQ+aHB3dme2Kerf8XY+vWkIISp7Za2ufKghtlnRXPyObAQQyvEJYrwMVTaCBlPEnSWcnHQz8Nka06YVOIeextNKZY3AQ=

Grab the key (which probably should be the latest one) that is written on the file from https://dl.carbslinux.org/keys/ so you can verify the signature. The latest Signify public key is also available on the package repository, so you can check the validity of the public key from multiple locations, or just copy paste that portion to a file and use that instead.

PUBKEY=carbslinux-2021.04.pub
wget https://dl.carbslinux.org/keys/$PUBKEY

You can now verify the distribution tarball with signify.

signify -V -m carbs-rootfs.tar.xz -p $PUBKEY

If everything went alright, this should output:

Signature Verified

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1.1.3 Extracting the tarball

You will need to extract the tarball to your desired location. For partitioning, you can follow this guide. This will assume that you will be mounting your root partition to ‘/mnt’.

mount /dev/sdx1 /mnt
tar xf carbs-rootfs.tar.xz -C /mnt

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1.1.4 Obtain the chroot helper

You can obtain the ‘cpt-chroot’ script in order to do a simple chroot into your new root filesystem.

wget https://dl.carbslinux.org/distfiles/cpt-chroot
chmod a+x cpt-chroot

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1.2 Chroot

Chroot into Carbs Linux!

./cpt-chroot /mnt

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1.2.1 Setting up repositories

Newest tarballs do not come with repositories, so you will need to manually obtain them, and set your ‘CPT_PATH’ environment variable. Carbs Linux repositories can either be obtained by ‘git’ or ‘rsync’. While rsync repositories are overall faster and smaller, git offers the whole history of the repository and a means to manipulate your repository as you like it. If you want to obtain the git repository, you will need to install ‘git’ itself.

The following guide will assume that you put the repositories into ‘~/repos/’ directory, but you can put the repositories into any directory you want. So go ahead and create that directory:

mkdir -p $HOME/repos
  1. Obtaining from git

    Carbs Linux git repositories can be found both from the main server and GitHub (mirror). Here are both their repository links. You can clone any of them.

    git clone git://git.carbslinux.org/repository $HOME/repos/carbs
    
  2. Obtaining from rsync

    Carbs Linux rsync repositories live in rsync://carbslinux.org/repo. In order to obtain it, run the following:

    rsync -avc rsync://carbslinux.org/repo $HOME/repos/carbs
    
  3. Making the package manager use the repositories

    In your shell’s configuration file, or in your ‘~/.profile’ file, add the following lines:

    CPT_PATH=$HOME/repos/carbs/core
    CPT_PATH=$CPT_PATH:$HOME/repos/carbs/extra
    CPT_PATH=$CPT_PATH:$HOME/repos/carbs/xorg
    CPT_PATH=$CPT_PATH:$HOME/repos/carbs/community
    export CPT_PATH
    

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1.2.2 Updating packages

It is good practice to make sure your system is up to date, especially before building new packages. If there is an update for the package manager you will need to update twice.

cpt-update && cpt-update

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1.2.3 Installing packages

Since you are operating on a really small base, you might need to build and install new programs to extend the functionality of your system. In order to build and install packages new packages in Carbs, you need to execute the following. "Package" is not actually a package and is given as an example.

cpt-build   package
cpt-install package

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1.2.4 Essential Software

Here is a list of software that you might want to have on your system.

BOOTLOADERS

FILESYSTEMS

NETWORKING

TEXT EDITORS

USER SHELLS

POSIX BASE UTILITIES

DOCUMENTATION


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1.2.5 Obtaining the documentation

All the documentation for Carbs Linux can be found on a single info manual to be viewed offline. You can obtain texinfo or the info (standalone) package in order to view the documentation.

# Install the documentation.
cpt b carbs-docs && cpt i carbs-docs

# Install either texinfo or the info package. We will be installing standalone info
# as it doesn't need perl.
cpt b info && cpt i info

# You can then run info and navigate through the documentation.
info carbslinux

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1.3 System Configuration

After you have finished installing some extra packages, you can configure your system to your liking.


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1.3.1 Configuring hostname

You might want to add a hostname, especially in a networked environment. Your hostname will default to ’carbslinux’ unless you set this.

echo your-hostname > /etc/hostname

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1.3.2 Hosts file

You can edit your /etc/hosts file, which is the static lookup table for host names. By default, there are two entries for localhost which are OKAY. You can replace the ’localhost’ part of these entries to your hostname.

127.0.0.1  localhost.localdomain localhost
::1        localhost.localdomain localhost ip6-localhost

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1.4 Kernel

Kernel isn’t managed under the main repositories, even though you could package one for your personal use. Here is an example kernel package, which you will need to reconfigure for your specific setup if you want to make use of it.


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1.4.1 Obtaining the kernel sources

You can visit the https://kernel.org website to choose a kernel that you want to install. Though only the latest stable and longterm (LTS) versions are supported.

# Download the kernel and extract it
wget https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.9.1.tar.xz
tar xf linux-5.9.1.tar.xz

# Change directory into the kernel sources
cd linux-5.9.1

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1.4.2 Kernel dependencies

In order to compile the kernel you will need to install some dependencies. You will need ‘libelf’, and ‘bison’ to compile the kernel. If you want to configure using the menu interface you will also need ‘ncurses’.

# The package manager asks to install if you are building more than one package,
# so no need to run 'cpt i ...'
cpt b libelf ncurses

In the vanilla kernel sources, you need perl to compile the kernel, but it can be easily patched out. You will need to apply the following patch. Patch was written by E5ten. You will need to obtain and apply the patch in the kernel source directory.

wget https://dl.carbslinux.org/distfiles/kernel-no-perl.patch
patch -p1 < kernel-no-perl.patch

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1.4.3 Building the kernel

Next step is configuring and building the kernel. You can check Gentoo’s kernel configuration guide to learn more about the matter. Overall, Gentoo Wiki is a good place to learn about configuration according to your hardware. The following will assume a monolithic kernel.

make menuconfig
make
install -Dm755 $(make -s image_name) /boot/vmlinuz-linux

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1.5 Making your system bootable

In order to be able to boot your fresh system, wou will need an init-daemon, init-scripts and a bootloader. The init daemon is already provided by busybox, but you can optionally change it.


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1.5.1 Bootloader

In the main repository, there is efibootmgr and grub to serve as bootloaders. efibootmgr can be used as a standalone bootloader, or can be used to install grub in a UEFI environment. efibootmgr is needed unless you are using a device without UEFI support (or you really want to use BIOS for a reason).

  1. GRUB BIOS installation
    cpt b grub && cpt i grub
    grub-install --target=i386-pc /dev/sdX
    grub-mkconfig -o /boot/grub/grub.cfg
    
  2. GRUB UEFI installation
    cpt b efibootmgr && cpt i efibootmgr
    cpt b grub && cpt i grub
    
    grub-install --target=x86_64-efi \
                 --efi-directory=esp \
                 --bootloader-id=CarbsLinux
    
    grub-mkconfig -o /boot/grub/grub.cfg
    

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1.5.2 Init scripts

Only thing left to do is installing the init-scripts, and now you are almost ready to boot your system!

cpt b carbs-init && cpt i carbs-init

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1.5.3 Fstab

You can now manually edit your fstab entry, or you can use the genfstab tool. If you want to use the tool, exit the chroot and run the following:

wget https://github.com/cemkeylan/genfstab/raw/master/genfstab
chmod +x genfstab
./genfstab -U /mnt >> /mnt/etc/fstab

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1.6 Post-installation

The base installation is now complete, you can now fine tune your system according to your needs. Rest of these instructions are completely optional. You can check the rest of the documentation to learn more about the system.


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1.6.1 KISS repositories

While not 100% compatible with cpt, you can use kiss repositories in your system the same way you are using the distribution repositories. Here is an example for the KISS Linux Community repository.


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2 Init System

Carbs Linux init scripts are run by the init daemon (‘busybox’ by default) on boot and shutdown processes. It also provides its own halting program named shalt. This provides a portable method that doesn’t rely on non-POSIX external programs.


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2.1 Configuring Init

There are three ways you can change the behaviour of the init system. Those are:


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2.1.1 Kernel Command Line

On GRUB, you can edit the kernel command line parameters, which will be parsed as variables on the init system. Not all of the parameters will be acted upon, but all of them will be set as variables on the init script. For example an example command line, and how it is interpreted.

BOOT_IMAGE=/boot/vmlinuz root=/dev/sda2 rw loglevel=3 quiet

This command line will be parsed to set the following variables:

BOOT_IMAGE=/boot/vmlinuz
root=/dev/sda2
rw=1
loglevel=3
quiet=1

Some of these variables, such as ‘rw=/=ro’, ‘loglevel’, and ‘quiet’, will be used by the init system to change the behaviour of the startup.


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2.1.2 ‘/etc/init/rc.conf’ file

However, the kernel command line isn’t the only place to set your boot parameters. You can specify variables here as well, although note that the kernel command line always gets the priority for these variables since they can be set just before boot.


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2.1.3 Init Hooks

Init hooks are for custom personal commands that the user may want to add to alter their boot. These can be used to load kernel modules, modify interfaces, and lot more. Those hooks are added to the ‘/etc/init’ directory with the hook name as the suffix. For example, a boot script will be placed as ‘/etc/init/my-hook.boot’. Currently, there are 4 hooks that the user can use.

early-boot

Run after pseudo-filesystems are mounted.

boot

Run before the boot stage is completed.

pre.shutdown

Run first when shutting down.

umount

Run just before filesystems are unmounted.

post.shutdown

Run just before the system is halted.


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2.2 Changing Init Program

By default, Carbs Linux comes preinstalled with ‘busybox-init’, but this can easily be replaced without any issues. Currently, available init systems are:

This example is for runit, but it will work with all init systems packaged in the distribution repositories. See the ‘cpt-alternatives(1)’ manual page for more details.

cpt a runit /usr/bin/init
cpt a runit /usr/bin/poweroff
cpt a runit /usr/bin/reboot

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2.2.1 Rebooting after changing init

After switching init systems, your running init system may not accept the new poweroff commands. You will need to reboot/poweroff using the running init’s utilities for the new utilities to work. These commands are for the init system currently running on your system and not the one you are switching to.

ProgramCommand
busyboxbusybox reboot
runitrunit-init 6
shinit/sinitkill -s INT 1

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3 Contribution Guidelines

Thanks for taking your time to contribute! To maintain stylistic behaviour throughout the repositories, one must adhere to these conventions. Exceptions and changes may occur with good reasoning.


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3.1 Conventions

[0010]

Try to keep the file readable.

[0011]

Characters on a line shouldn’t exceed 100 characters.

[0012]

Make sure you don’t have code commented out during commit. Uncomment them or remove them completely.

[0013]

Do not add comments following the code, add them to the top of the code. It makes it harder to read, and lines longer. Here is an example:

# Good way of commenting.
your code goes here

your code goes here  # Avoid this way of commenting.

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3.1.1 Shell Conventions

Shell is central to Carbs Linux projects. Most of the tools and packages are written in POSIX sh.

[1010]

Use 4 spaces for indentation, don’t use tabs.

[1020]

Make sure you don’t use bash-specific code.

[1030]

Make sure you lint your code with ‘shellcheck’ and if you are new to POSIX sh, use ‘checkbashisms’.

[1040]

Don’t spawn new processes if you don’t absolutely need to, especially during string manipulation.

[1041]

Never use a program for text manupilation that isn’t defined in the POSIX standard. This includes ‘gawk’ and ‘perl’.

[1042]

Instead of $(basename $file), use ${file##*}.

[1043]

Instead of $(dirname $file), use ${file%/*}.

# This is the same thing as basename /path/to/test.asc .asc

$ file=/path/to/test.asc file=${file##*/} file=${file%.asc}
$ echo $file
test
[1050]

Instead of backticks, use $(..).


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3.1.2 Repository Conventions

Repository conventions are important in order to ensure every package resemble themselves. Here are the things to keep in mind:

[2010]

Prefer tarballs over git packages unless there is a sensible reason. Here are some:

[2020]

Prefer sources without a dependency to ‘automake’. There are usually distribution tarballs that are ‘autoconf’’ed. Don’t submit tarballs with an automake dependency unless you are ‘sure’ there is no alternative.

[2030]

Avoid these packages:

dbus

Usually can be disabled by --disable-dbus.

gettext

Usually can be disabled by --disable-nls.

[2040]
[2050]

All build files on the repository should be a POSIX shell script, and must start with #!/bin/sh -e.

The next section is about package templates that should be used in order to ensure stylistic consistency. Note that the option configurations shouldn’t be taken literally, they are meant as examples.

  1. Make [2210]
    #!/bin/sh -e
    
    make
    make DESTDIR="$1" PREFIX=/usr install
    
  2. Configure/Make [2211]
    #!/bin/sh -e
    
    ./configure \
        --prefix=/usr \
        --disable-option \
        --enable-option
    
    make
    make DESTDIR="$1" install
    
  3. Autoconf/Automake [2212]

    See 2020

    #!/bin/sh -e
    
    autoreconf -fi
    
    ./configure \
        --prefix=/usr \
        --disable-option \
        --enable-option
    
    make
    make DESTDIR="$1" install
    
  4. Meson [2220]
    #!/bin/sh -e
    
    export DESTDIR=$1
    
    meson \
        --prefix=/usr \
        -Doption=false \
        -Doption2=true \
        . output
    
    ninja -C output
    ninja -C output install
    
  5. Cmake [2230]
    #!/bin/sh -e
    
    export DESTDIR=$1
    
    cmake -B build \
        -DCMAKE_INSTALL_PREFIX=/usr \
        -DCMAKE_BUILD_TYPE=Release \
        -DOPTION=ON
    
    cmake --build   build
    cmake --install build
    
  6. Go [2240]
    #!/bin/sh -e
    
    export GOPATH=$PWD/gopath
    trap "go clean -modcache" EXIT INT
    go mod vendor
    
    go build
    install -Dm755 program "$1/usr/bin/program"
    
  7. Python [2241]
    #!/bin/sh -e
    
    python setup.py build
    python setup.py install --prefix=/usr --root="$1"
    

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Appendix A GNU Free Documentation License

Version 1.3, 3 November 2008
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
  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.

  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.

    The "publisher" means any person or entity that distributes copies of the Document to the public.

    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.

  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.

  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.

  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:

    1. 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.
    2. 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.
    3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
    4. Preserve all the copyright notices of the Document.
    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
    6. 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.
    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document’s license notice.
    8. Include an unaltered copy of this License.
    9. 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.
    10. 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.
    11. 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.
    12. 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.
    13. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.
    14. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.
    15. 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.

  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."

  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.

  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.

  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.

  10. TERMINATION

    You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

  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. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

  12. RELICENSING

    "Massive Multiauthor Collaboration Site" (or "MMC Site") means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A "Massive Multiauthor Collaboration" (or "MMC") contained in the site means any set of copyrightable works thus published on the MMC site.

    "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    "Incorporate" means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is "eligible for relicensing" if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

A.1 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 1.3
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.