ACPI: Advanced Configuration and Power Interface

Emma Jane Hogbin

Erich Schubert - Author of the section on DSDT.

Revision History
Revision v1.5.12004-07-15Revised by: ejh
Link included to the French translation of this document.
Revision v1.52004-05-21Revised by: ejh
Minor updates for the 2.6.6 kernel and corrections regarding which kernels need patching.
Revision v1.42004-05-12Revised by: ejh
Initial thoughts on the 2.6.5 kernel; includes information on battery monitoring applications causing touchpad lockup problems.

Outlines how to patch a kernel for ACPI support.

Table of Contents
1. About this document
2. Copyright and License
3. Translations
4. About ACPI
5. Why switch?
6. DSDT: Differentiated System Description Table
7. Installing from scratch
7.1. Choosing a kernel
8. Backups
9. Download and Unpack the New Kernel
9.1. Required packages
9.2. Unpack
10. Configure the new kernel
11. Compile the new kernel
12. Install the new kernel
13. Reboot and test
14. Load related modules
15. Switching from APM to ACPI
16. Using ACPI
17. References and Resources
18. Thanks
A. Patching Old Kernels
A.1. Getting the Source Files
B. ACPI the Non-Debian Way
B.1. Compile the kernel
B.2. Install the new kernel
B.3. Software packages
C. GNU Free Documentation License
C.12. How to use this License for your documents

1. About this document

When I first started the switch from APM to ACPI I didn't realize the kernel needed to be patched. My problem (insanely loud fan) was fixed just by upgrading to 2.4.20 (Debian packaged kernel with an earlier patch from Unfortunately after the first upgrade I wasn't able to halt my computer without using the power switch to power-down my computer. It wasn't until later that I realized I had an old, ineffectual ACPI patch. This HOWTO was written to summarize the install process for myself, and hopefully help others who are also having a hard time finding information about ACPI. Please note: the main article outlines The Debian Way of doing things. There is also generic information in the Appendix B for those of you who prefer ... the generic way.

2. Copyright and License

Copyright (c) 2003, 2004 Emma Jane Hogbin.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in Appendix C.

3. Translations

This document is also available in the following languages:

4. About ACPI

In the world of power management ACPI is relatively new to the game. It was first released in 1996 by Compaq/Hewlett-Packard, Intel, Microsoft, Phoenix and Toshiba. These developers aimed to replace the previous industry standard for power management. Their site contains the official specifications, a list of companies that support ACPI and a number of other goodies. This is definitely not required reading, but may be of some interest to the insanely curious.

ACPI allows control of power management from within the operating system. The previous industry standard for power management, Advanced Power Management (APM), is controlled at the BIOS level. APM is activated when the system becomes idle--the longer the system idles, the less power it consumes (e.g. screen saver vs. sleep vs. suspend). In APM, the operating system has no knowledge of when the system will change power states.

ACPI can typically be configured from within the operating system. This is unlike APM where configuration often involves rebooting and entering the BIOS configuration screens to set parameters.

ACPI has several different software components:

If you would like more information on power management in laptops, check out the resources on Specifically: Power Management with Linux - APM, ACPI, PMU and the Hardware in Detail section of the Linux Mobile Guide.

5. Why switch?

Not all systems support both APM and ACPI. I switched because my system only supported ACPI. Pretty easy decision really. If you're switching to get S3 (suspend to RAM) support and you're using a 2.4.x kernel, don't bother. It is not supported. Period.

Not sure if your system is supported? ACPI4Linux has a list of supported machines/BIOSes started on their Wiki. Please contribute to the list if you've installed ACPI! They also have a list of machines that are not supported.

For more information about the power management in laptops you may (also) find the Battery Powered Linux Mini-HOWTO useful.

6. DSDT: Differentiated System Description Table

Thanks to Erich writing this section.

You might need to override the DSDT when certain features like battery status are incorrectly reported (usually causing error messages to syslog). DELL laptops usually need this kind of override. Fixed DSDT for many systems are available on the DSDT page, along with a patch that tells the kernel to ignore the BIOS-supplied table but use the compiled-in fixed DSDT.

Basically you need to copy the fixed table into your kernel source with a special filename (or modifying the filename in the patch supplied at the DSDT page) This override is quite easy: instead of loading the DSDT table from bios, the kernel uses the compiled-in DSDT table. That's all.

7. Installing from scratch

ACPI is constantly being revised. It is available in later versions of the 2.4.x series kernel (2.4.22 and higher), and all 2.6.x series kernels. If you would like to use a kernel before 2.4.22, you will need to patch your kernel source to add ACPI functionality. If at all possible you should use the latest stable version of the kernel. Patches are available from

Red Hat Fedora Core 2 now ships with ACPI enabled by default! This is big progress for the ACPI development team. Congratulations to everyone.


Even the latest kernel will sometimes have minor bug fixes available as a patch. You should check the ACPI4Linux web site to see if there are any patches available.

You need to get the patch that exactly matches the version of the kernel that you are running. Since this is the "install from scratch" section I will assume you know exactly which kernel you will be installing.

7.1. Choosing a kernel

This document was originally written for the 2.4.20 kernel and has been updated since to include information about the 2.6.x series kernels. At the time of this update the 2.6.x series kernels are proving easy for some and harder for others. (I personally cannot properly power down my computer with the 2.6.5 kernel.)

If you can, I would recommend waiting to upgrade your kernel to the 2.6.x series until more bugs are ironed out. There are a lot of changes in the 2.6.x series kernel. When I upgraded to 2.6.5 to update this document I ran into problems with my wireless connection, my nvidia graphics card, and with ACPI. Your mileage may vary. I personally had good success with the 2.4.20 with the latest patch and the 2.4.22 kernel with no patch. A Google through your distribution's mailing list, and the acpi-devel mailing list should help you to pick the right kernel.


This document uses the 2.4.20 kernel as an example for 2.4.x series kernels. Substitute your own kernel version as appropriate.

Regardless of which kernel you choose, if it is a kernel that requires patching, it is important to use the latest version of the ACPI patch. Some distributions have already patched their kernels. This is the case for Debian, and may be the case for others. For more information on the patches that have been applied to the Debian kernel source package scan through: /usr/src/kernel-source-<version>/README.Debian. If you are not using Debian you will probably still be able to find an equivalent file for your distribution.

A user on acpi-support confirmed that I shouldn't need any of the additional patches that have been applied to the kernel to run my laptop. If you are running a production-level server and/or are serving web pages to the internet, you should really apply any additional security patches.


If a kernel has had other patches applied to it, you may have problems applying the ACPI patch. Of course, an ACPI patch should not be applied to a kernel that is already patched for ACPI. As long as there has not been an ACPI patch applied to the kernel it should be possible to apply one now. Depending on the patches applied, you may need to modify some of the Makefiles for your patch to be successful. This is beyond my current grasp of reality so it is not covered in this document.

7.1.1. Debian-ized pre-patched kernel

If you would prefer to use a Debian-ized kernel instead of a fresh one, maxx has provided a pre-patched kernel-source package with the latest patch for the 2.4.20 kernel. This would be instead of downloading a fresh (non-patched) kernel from He sent me an email with the following details:


I took the kernel-source 2.4.20-8 from unstable, removed the ACPI changes [i.e. the old patch] and applied acpi-20021212-2.4.20.diff.gz from since the vanilla 2.4.20 HAS several security leaks (ptrace, hash table, ...).

You can find the package at (I didn't upload the .orig.tar.gz since you can get it from any debian mirror and the .deb is already big enough)



I have not tested these packages. You may or may not have any luck with them. Please don't email me asking about them, ask maxx instead.

8. Backups

If you are already running a kernel that is the same version of the one you are about to patch I recommend creating a fresh directory for the newly patched kernel. Remember that backups are never a bad thing. These are the files that I back up:

9. Download and Unpack the New Kernel

9.1. Required packages

The following is a list of packages required to patch a 2.4.x series kernel. I am still working on the notes for a 2.6.x series install.

2.4.x series kernels

  • kernel source files

  • ACPI patch that exactly matches the kernel version

  • debian packages: make, bzip2, gcc, libc6-dev, tk8.3, libncurses5-dev, kernel-package

  • after you've patched the kernel add the debian packages: acpid, acpi (this last package is available in testing and unstable versions of Debian, but not stable)

9.2. Unpack

We need to unpack the bz2 file (bzip2) and shuffle the directories around a bit. /usr/src/linux probably points to your current kernel. We need it to point to the new kernel, so we'll do that as well.

  • cd /usr/src

  • mkdir kernel-source-<version> (use an alternate name if you already have a version of this kernel installed)

  • cp linux.<version>.tar.bz2 /usr/src/kernel-source-<version>

  • cd /usr/src/kernel-source-<version>

  • tar xjfv linux.<version>.tar.bz2

  • mv linux.<version> /usr/src/linux-<version>

  • rm linux (assuming that's a link to your old kernel)

  • ln -s /usr/src/linux-<version> linux

If your kernel needs to be patched, do so now. Instructions are available from Appendix A.

10. Configure the new kernel

NotePatch Your Kernel First

If you are using an old kernel you will need to patch it before you can proceed. Instructions on patching your kernel are available from Appendix A. The 2.6.x series kernels do not need to be patched.

Now instead of using make menuconfig, I have an excellent alternative. Check this out: copy your current .config file into /usr/src/linux. Now use "make oldconfig". It will run through your old config file and see what's been updated so that you don't have to find all the new options. For everything to do with ACPI and your specific hardware (Toshibas choose the Toshiba options, Asus choose the Asus options) choose M for module. There are about ten different ACPI related options that you will need to select.

In point form, this is how the kernel should be configured:

Now go in to the config file with make menuconfig. I want you do check and make sure you have your APM (the old stuff) turned off. Under "General Setup", make sure that:

exit and save the new configuration

11. Compile the new kernel

If you have additional modules that are not part of the main source tree, you will need to add modules_image when you make your Debian packages. This is almost inevitable if you're using a laptop and an older kernel. Only my nvidia graphics card now requires additional modules.

NoteNaming kernel builds

I no longer use .date to distinguish kernel builds. It was too frustrating to have 030627a, 032627b (etc) as I tried to figure things out. I now use names, in alphabetical order, starting with the kernel build "alien". I'm going to leave the date option in though as I still think it's a good way to do things.

My current kernel, 2.6.6, is "Elrond." The machine itself is "Smeagol."

NoteKernel compile help

For non-Debian instructions see the Appendix "Appendix B".

For more information on how to compile the kernel The Debian Way please read Creating custom kernels with Debian's kernel-package system

12. Install the new kernel

I like to configure lilo on my own, but do whatever tickles your fancy.

NoteKernel compile help

For non-Debian instructions see the Appendix "Appendix B".

For more information on how to compile the kernel The Debian Way please read Creating custom kernels with Debian's kernel-package system

13. Reboot and test

At this point you should reboot your machine. When your system comes back up (assuming of course that everything went well and you still have a system), check to see what kernel you're running with uname -a. It should show you the one you just built. You also need to make sure the correct patch was installed. You can do that with dmesg | grep ACPI.*Subsystem\ revision . It should give the output: ACPI: Subsystem revision 20021212. The revision is the date the patch was released. This number will be different than mine if you are not using the 2.4.20 kernel. To look at all ACPI-related bits that were loaded/started when your system rebooted, do this: dmesg | grep ACPI . dmesg prints your boot messages and grep ACPI makes sure that only ACPI-related messages are printed.

You can also check to see what version you're using with cat /proc/acpi/info. Don't believe everything you read though. My output says that S3 is a supported state, but we already know it's not. It does give the correct version though, which is useful.

14. Load related modules

Check to see that each of the ACPI modules have been loaded after your machine boots. You can do this with the command lsmod. You are looking for the following options: button, battery, fan, ac, thermal and processor. If you chose "Y" instead of modules when you compiled your kernel, you will not see this list. The output on my computer looks like this:

Module                  Size  Used by    Tainted: P  
button                  2420   0 (unused)
battery                 5960   0 (unused)
ac                      1832   0 (unused)
fan                     1608   0 (unused)
thermal                 6664   0 (unused)
processor               8664   0 [thermal]
NVdriver              945408  11 

The last module is my graphics card, which uses proprietary drivers. This is why I have a "P" next to Tainted on the top line.

If you compiled ACPI support in as "M"odules and you don't see the ACPI modules listed you will need to load the modules by hand. The modules should be in /lib/modules/<version>. <date>/kernel/drivers/acpi/, and are as follows:

-rw-r--r--    1 root     root         4.1k Jun  3 23:57 ac.o
-rw-r--r--    1 root     root         9.5k Jun  3 23:57 battery.o
-rw-r--r--    1 root     root         5.2k Jun  3 23:57 button.o
-rw-r--r--    1 root     root         3.7k Jun  3 23:57 fan.o
-rw-r--r--    1 root     root          14k Jun  3 23:57 processor.o
-rw-r--r--    1 root     root          11k Jun  3 23:57 thermal.o
-rw-r--r--    1 root     root         6.2k Jun  3 23:57 toshiba_acpi.o

NoteExtensions on Modules

The module name is the bit before .o extension on a module filename. processor.o is the file, and processor is the module name. To install a loadable kernel module use: insmod processor.

The 2.4.x series kernels use the extension .o; however, the 2.6.x series kernel use the extension .ko.

The first time I rebooted I loaded them all by hand, typing insmod <modulename>. I personally load processor first, although there are mixed feelings on whether or not the order matters.

NoteOperating System Power Management (OSPM)

The first time I tried this the modules were all in separate directories and were ospm_<name>. This was probably because I was using an old patch, but it is something to be aware of. The OSPM modules are now deprecated so hopefully you won't see them.

To prevent having to load the modules each time you reboot you can do one of two things: compile them directly into the kernel (bit late for that though, eh?), or add them to your /etc/modules file. If you don't already have a copy of the file just create a new one and add each module name (remember, no dot-o) on a separate line. You can also try running update-modules which should automatically update your /etc/modules.conf configuration file.

15. Switching from APM to ACPI

Do not let apmd and acpid run at the same time unless you REALLY know what you're doing. Debian will not make sure only one is running at a time. You will have to check. APM will try to put your system into S3. On the 2.4.x (and before) series kernels this will quite probably hang your machine. S3 is not supported until at least 2.5.x. Even the patch won't provide support for S3 in the 2.4.x series kernels. I personally did an apt-get remove apmd to solve the hanging problem.

You should also be aware of another little glitch I discovered. The XFree86 server has an option for DPMS (Energy Star) features. The DPMS can states can be one of standby, suspend, off or on. Since the 2.4.x kernels cannot suspend to disk, this can cause problems. I fixed my system by doing two things:

WarningLost Touchpad and Keyboard Interrupts

Karl Hegbloom emailed me to say that "keyboard keys sticking, touchpad pointer jumping suddenly across the screen, lockups under heavy network I/O [was] caused by polling the battery state via ACPI and the proc file system." This problem caused, in part, by a delay between the initial request for information about the battery's status and the response. In that delay interrupts may be locked out and synchronization with the keyboard and touch pad may be lost. "The overnight solution is to either turn off the battery applet, or reduce its polling frequency." Karl also notes that a BIOS update was also able to solve the problem. Thanks Karl!

I did not find this to be a problem for me in the 2.4.x kernels, however, it was a problem when I upgraded to 2.6.5. I use wmacpi to monitor my battery status. By setting the polling frequency to 1 (the lowest possible number), I seem to have eliminated the touchpad lockups. In my .xinitrc file I use:

/usr/bin/wmacpi -s 1

The -s 1 represents the polling frequency (sample rate) of "once per minute." The default is 20.

16. Using ACPI

There are a few different applications/daemons you will want to install on your system: acpid (the daemon that will control your hardware states), and acpi (the interface to monitor events and states) are the base install. The acpi Debian package is only available in testing and is unstable. If you're running stable you won't be able to install it without playing around with apt and your list.sources file. You can probably also compile from source. If you do get acpi installed you can use it to monitor your system like this: acpi -V. The output will tell you about your system. Mine looks like this:

     Thermal 1: ok, 47.1 degrees C
     Thermal 2: ok, 45.1 degrees C
  AC Adapter 1: off-line <-- running off battery
  AC Adapter 1: on-line <-- running off AC power

Unfortunately, the -V "full version" doesn't work for me. Fortunately I can still look in each of the acpi files individually for information about my system. Check in the /proc/acpi directory for various things of importance. If I want to check my battery I read the following file like this: cat /proc/acpi/battery/BAT0/state. The output is as follows:

present:                 yes
capacity state:          ok
charging state:          discharging <-- running off battery
present rate:            unknown
remaining capacity:      3920 mAh <-- watch this number
present voltage:         14800 mV

present:                 yes
capacity state:          ok
charging state:          discharging
present rate:            unknown
remaining capacity:      3840 mAh <-- capacity getting smaller
present voltage:         14800 mV

present:                 yes
capacity state:          ok
charging state:          charging <-- AC adapter plugged in
present rate:            unknown
remaining capacity:      3840 mAh
present voltage:         14800 mV

If I want information about my battery in general I check it out like this: cat /proc/acpi/battery/BAT0/info

present:                 yes
design capacity:         3920 mAh
last full capacity:      3920 mAh
battery technology:      rechargeable
design voltage:          14800 mV
design capacity warning: 30 mAh
design capacity low:     20 mAh
capacity granularity 1:  10 mAh
capacity granularity 2:  3470 mAh
model number:            Bat0
serial number:              
battery type:            Lion
OEM info:                Acer

You're smart people. You can probably figure it out from here. :)

17. References and Resources

The following URLs were incredibly useful in writing this HOWTO and generally getting ACPI up and running.


HOWTO install ACPI under Linux


Linux on the road, formerly: Linux Laptop HOWTO You'll need to scroll a bit, or use the HTML version:

Hardware in Detail (part of Linux on the road)

Power Management with Linux - APM, ACPI, PMU

Battery Powered Linux Mini-HOWTO

Creating custom kernels with Debian's Kernel-Package system

Hardware-specific Install Reports and Info

Installation Reports


DSDT: Overview Includes links to patched DSDTs and HOWTOs about patching your own DSDT.

BIOS Settings for the AcerTM (Phoenix BIOS)

Software Development Groups


ACPI Special Interest Group


ACPI articles

Fan Speed Control Techniques in PCs

ACPI packages and related software

The Kernel

Remember to choose "F" for full when you download your kernel source.

Debian-ized kernel

maxx's pre-patched 2.4.20-8 kernel source package. For more information see maxx's notes.

ACPI kernel patch

You'll need to pick the version that exactly matches the kernel you're using.


the daemon


text interface


graphical interface for KDE


another KDE interface


WindowMaker DockApp (another GUI)


WindowMaker DockApp (another graphical interface). Handles two battery slots.

18. Thanks

Much thanks goes out to the following:

A. Patching Old Kernels

If you are using a 2.4.x series kernel, the kernel will need to be patched before you can add ACPI support. Although ACPI is included in the 2.6.x series kernels you should check to see if any patches have been released to fix bugs. You can find this information on the ACPI4Linux site.

A.1. Getting the Source Files

Download a fresh kernel from You need to make sure you get a full kernel. Find the "latest stable version of the Linux kernel" and click on F for FULL. Wait patiently. A bzipped kernel is about 26M. If you're feeling particularly geeky you could also wget<version>.tar.bz2.


You may or may not want the latest stable version. For more information read the Section 7.1 section of this document. If you decide to use a version of the kernel that is not published on the front page, use the /pub/linux/kernel directory on the site to find the kernel you'd like.

While you're waiting, grab a copy of the patch as well. For the 2.4.20 kernel use the 2.4.20 patch. It's dated 2002.12.12. You'll need to know that number later when we check to make sure the patch worked. If you are using a different kernel version make sure you take note of the date of your patch. Your numbers will differ slightly from the one I use later on.

Once you've got those two files (the kernel and the patch) unpack them and patch the kernel.

A.1.1. Patch

Now we're going to actually patch the kernel. I take one extra step from the instructions at ACPI4Linux. Instead of gunzipping and patching in the same line, I use two lines. This is purely a matter of preference. When you patch the kernel you want to make sure there are no error messages. (There is no "yay" line, instead look for the absence of errors.)

  • cd /usr/src/linux

  • cp acpi-20021212-2.4.20.diff.gz /usr/src/linux/. (Your patch filename will be different if you're not using the 2.4.20 kernel.)

  • gunzip acpi-20021212-2.4.20.diff.gz

  • patch -p1 < acpi-20021212-2.4.20.diff (this is the actual patching part)

Once you've finished patching your kernel, continue reading at Section 10.

B. ACPI the Non-Debian Way

There is very little difference between The Debian Way and the generic way. In fact it's probably only 10 or so lines of difference.

B.1. Compile the kernel

The "normal" way of compiling a kernel does not use make-kpkg. Instead, it uses the following steps:

  • cd /usr/src/linux which should point to the 2.4.20 kernel (unzipped) files

  • make dep

  • make clean

  • make bzImage

  • make modules (remember to unpack your modules first)

B.2. Install the new kernel

In The Debian Way, you create a deb file which contains information about where the kernel is (and makes the kernel and yada-yada). In the "normal" way, you put things where they need to be right away. You need to install your modules and then configure lilo to point to the new kernel and then run lilo. If you are not doing things The Debian Way your "install" will look like this:

  • cd /usr/src/linux

  • make modules_install

  • cp arch/i386/boot/bzImage /boot/vmlinuz.<date>

  • vi /etc/lilo.conf and copy the structure of your existing kernel. Do NOT delete the reference to your existing kernel! You need to point lilo to the "vmlinuz" file that was created when you compiled the kernel above

  • lilo (yup, just exactly like that.) Lilo will let you know if it's going to have major problems loading the new kernel.


Do NOT forget to run lilo before rebooting. Type lilo. It's that easy (and that easy to forget).

B.3. Software packages

You can still use all of the software mentioned in this HOWTO even if you're not using Debian. Unfortunately it will take a little more effort on your part to download and install everything. Fortunately it's really not that difficult. Most software packages include a README file when you gunzip them which will explain what you need to do to get things working on your system.

TipSoftware downloads

For more information about software for ACPI, please use the ACPI packages and related software.

C. GNU Free Documentation License

Version 1.1, March 2000

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You may also lend copies, under the same conditions stated above, and you may publicly display copies.


If you publish printed copies 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 publicly-accessible computer-network location containing a complete Transparent copy of the Document, free of added material, which the general network-using public has access to download anonymously at no charge using public-standard network protocols. 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.


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 less than five).

  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", and 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. In any section entitled "Acknowledgements" or "Dedications", preserve the section's title, 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 as "Endorsements" or to conflict in title with any Invariant Section.

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.


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.

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."


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.


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, does not as a whole count as a Modified Version of the Document, provided no compilation copyright is claimed for the compilation. Such a compilation is called an "aggregate", and this License does not apply to the other self-contained works thus compiled with the Document, on account of their being thus compiled, if they 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 quarter of the entire aggregate, the Document's Cover Texts may be placed on covers that surround only the Document within the aggregate. Otherwise they must appear on covers around the whole aggregate.


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 provided that you also include the original English version of this License. In case of a disagreement between the translation and the original English version of this License, the original English version will prevail.


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.


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

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.

C.12. 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 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. A copy of the license is included in the section entitled "GNU Free Documentation License".

If you have no Invariant Sections, write "with no Invariant Sections" instead of saying which ones are invariant. If you have no Front-Cover Texts, write "no Front-Cover Texts" instead of "Front-Cover Texts being LIST"; likewise for Back-Cover Texts.

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.