582 lines
29 KiB
Plaintext
582 lines
29 KiB
Plaintext
Bridging mini-HOWTO
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Christopher Cole
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cole@coledd.com
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March 2001
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Revision History
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Revision 1.22 2002-05-20 Revised by: tab
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Converted to Docbook 4.1 SGML and added GFDL per Christopher Cole
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Revision 1.21 2001-03-07 Revised by: cc
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This document describes how to setup an ethernet bridge. What is an ethernet
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bridge? An ethernet bridge is a device that controls data packets within a
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subnet in an attempt to cut down the amount of traffic. A bridge is usually
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placed between two separate groups of computers that talk within themselves,
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but not so much with the computers in the other group. A good example of this
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is to consider a cluster of Macintoshes and a cluster of unix machines. Both
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of these groups of machines tend to be quite chatty amongst themselves, and
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the traffic they produce on the network causes collisions for the other
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machines who are trying to speak to one another. A bridge would be placed
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between these groups of computers. The job of the bridge is then to examine
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the destination of the data packets one at a time and decide whether or not
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to pass the packets to the other side of the ethernet segment. The result is
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a faster, quieter network with less collisions.
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-----------------------------------------------------------------------------
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Table of Contents
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1. Setup
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2. Common Problems
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3. Copyright
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3.1. GNU Free Documentation License
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3.2. PREAMBLE
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3.3. APPLICABILITY AND DEFINITIONS
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3.4. VERBATIM COPYING
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3.5. COPYING IN QUANTITY
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3.6. MODIFICATIONS
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3.7. COMBINING DOCUMENTS
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3.8. COLLECTIONS OF DOCUMENTS
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3.9. AGGREGATION WITH INDEPENDENT WORKS
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3.10. TRANSLATION
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3.11. TERMINATION
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3.12. FUTURE REVISIONS OF THIS LICENSE
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3.13. How to use this License for your documents
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1. Setup
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* Get Bridge Config: [ftp://ftp.tux.org/people/alan-cox/BRCFG.tgz]
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BRCFG.tgz
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* BRCFG may also be found at: [http://coledd.com/networking/bridge/] http:/
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/coledd.com/networking/bridge
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* Enable multiple ethernet devices on your machine by adding this line to
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your /etc/lilo.conf, and re-run lilo:
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+---------------------------------------------------------------+
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|append = "ether=0,0,eth1" |
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+---------------------------------------------------------------+
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If you have three interfaces on your bridge, use this line instead:
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+---------------------------------------------------------------+
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|append = "ether=0,0,eth1 ether=0,0,eth2" |
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+---------------------------------------------------------------+
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More interfaces can be found by adding more ether statements. By default
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a stock Linux kernel probes for a single ethercard, and once one is found
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the probe ceases. The above append statement tells the kernel to keep
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probing for more ethernet devices after the first one is found.
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Alternatively, the boot parameter can be used instead:
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+---------------------------------------------------------------+
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|linux ether=0,0,eth1 |
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+---------------------------------------------------------------+
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Or, with 3 interfaces, use:
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+---------------------------------------------------------------+
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|linux ether=0,0,eth1 ether=0,0,eth2 |
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+---------------------------------------------------------------+
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* Recompile the kernel with BRIDGING enabled.
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* A bridge should not have an IP address. It CAN, but a plain bridge
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doesn't need one. To remove the IP address from your bridge, go to /etc/
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sysconfig/network-scripts/ (for a RedHat system) and copy ifcfg-lo0 to
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ifcfg-eth0 & ifcfg-eth1. In these two new files, change the line
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containing DEVICE=lo to DEVICE=eth0 and DEVICE=eth1. Since other
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distributions may deviate from this, you may need to refer to additional
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documentation. If there are more than 2 interfaces to this bridge, be
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sure to make the corresponding configurations to those, as well.
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* Reboot so you are running the new kernel with BRIDGING in it, and also to
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make sure that an IP addresses are not bound to the network interfaces.
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* Once the system is backed up, put the ethernet cards into promiscuous
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mode, so they will look at every packet that passes by its interface:
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+---------------------------------------------------------------+
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|ifconfig eth0 promisc ; ifconfig eth1 promisc |
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+---------------------------------------------------------------+
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All interfaces which are connected to network segments to be bridged are
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to be put into promiscuous mode.
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* Turn bridging ON using the brcfg program:
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+---------------------------------------------------------------+
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|brcfg -ena |
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+---------------------------------------------------------------+
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* Verify that there is different traffic on each interface:
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+---------------------------------------------------------------+
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|tcpdump -i eth0 (in one window) |
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|tcpdump -i eth1 (in another window) |
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| |
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+---------------------------------------------------------------+
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* Run a sniffer or tcpdump on another machine to verify the bridge is
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separating the segment correctly.
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-----------------------------------------------------------------------------
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2. Common Problems
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Q: I get the message ioctl(SIOCGIFBR) failed: Package not installed . What
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does this mean?
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Q: Machines on one side cannot ping the other side!
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Q: I cannot telnet/ftp from the bridge! Why?
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Q: What do I need to set up in the way of routing?
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Q: The bridge appears to work, but why doesn't traceroute show the bridge as
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a part of the path?
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Q: Is it necessary to compile IP_FORWARD into the kernel?
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Q: Why are the physical ethernet addresses for port 1 and port 2 the same
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according to the brcfg program? Shouldn't they be different?
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Q: Bridging does not appear to be an option when performing a make config on
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the kernel. How does one enable it?
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Q: Too many hubs (4 or more) are chained one after another in series, cause
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timing problems on an ethernet. What effect does a bridge have in a
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subnet that is layered with hubs?
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Q: Can a bridge interface to both 10Mb and 100Mb ethernet segments? Will such
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a configuration slow down the rest of the traffic on the high speed side?
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Q: I get the message ioctl(SIOCGIFBR) failed: Package not installed . What
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does this mean?
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A: You don't have bridging capability in your kernel. Get a 2.0 or greater
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kernel, and recompile with the BRIDGING option enabled.
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Q: Machines on one side cannot ping the other side!
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A:
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Did you enable bridging using brcfg -ena? (brcfg should say bridging is
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ENABLED)
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Did you put the interfaces into promiscuous mode? (issue the ifconfig
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command. The PROMISC flag should be on for both interfaces.)
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If using multiple-media interface adapters, make sure that the correct one is
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enabled. You may need to use the config/setup program that came with the
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network interface card.
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Q: I cannot telnet/ftp from the bridge! Why?
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A: This is because there is no IP address bound to any of bridge interfaces.
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A bridge is to be a transparent part of a network.
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Q: What do I need to set up in the way of routing?
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A: Nothing! All routing intelligence is handled by the bridging code in the
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kernel. To see the ethernet addresses as they are learned by the bridge, use
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the brcfg program in debug mode:
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+---------------------------------------------------------------------------+
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|brcfg -deb |
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| |
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+---------------------------------------------------------------------------+
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Q: The bridge appears to work, but why doesn't traceroute show the bridge as
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a part of the path?
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A: Due to the nature of a bridge, a traceroute should NOT show the bridge as
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a part of the path. A bridge is to be a transparent component of the network.
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Q: Is it necessary to compile IP_FORWARD into the kernel?
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A: No. The bridging code in the kernel takes care of the packet transport.
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IP_FORWARD is for a gateway that has IP addresses bound to its interfaces.
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Q: Why are the physical ethernet addresses for port 1 and port 2 the same
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according to the brcfg program? Shouldn't they be different?
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A: No. Every port on a bridge intentionally is assigned the same physical
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ethernet address by the bridging code.
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Q: Bridging does not appear to be an option when performing a make config on
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the kernel. How does one enable it?
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A: During the kernel config, answer "Y" to the question, Prompt for
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development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL) [Y/n/?].
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Q: Too many hubs (4 or more) are chained one after another in series, cause
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timing problems on an ethernet. What effect does a bridge have in a subnet
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that is layered with hubs?
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A: A bridge resets the 3/4/5 hubs rule. A bridge does not deal with packets
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the way a hub does, and is therefore not a contributor to timing problems on
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a network.
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Q: Can a bridge interface to both 10Mb and 100Mb ethernet segments? Will such
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a configuration slow down the rest of the traffic on the high speed side?
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A: Yes, a bridge can tie together a 10Mb segment with a 100Mb segment. As
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long as the network card on the fast network is 100Mb capable, TCP takes care
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of the rest. While it's true that the packets from a host in the 100Mb
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network communicating to a host in the 10Mb network are moving at only 10Mb/
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s, the rest of the traffic on the fast ethernet is not slowed down.
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-----------------------------------------------------------------------------
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3. Copyright
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Copyright © 2002 Christopher Cole
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Permission is granted to copy, distribute and/or modify this document under
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the terms of the GNU Free Documentation License, Version 1.1 or any later
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version published by the Free Software Foundation; with no Invariant
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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".
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||
-----------------------------------------------------------------------------
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||
3.1. GNU Free Documentation License
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|
||
Version 1.1, March 2000
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||
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Copyright (C) 2000 Free Software Foundation, Inc. 59 Temple Place, Suite
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330, Boston, MA 02111-1307 USA Everyone is permitted to copy and
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distribute verbatim copies of this license document, but changing it is
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not allowed.
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-----------------------------------------------------------------------------
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3.2. PREAMBLE
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The purpose of this License is to make a manual, textbook, or other written
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document "free" in the sense of freedom: to assure everyone the effective
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freedom to copy and redistribute it, with or without modifying it, either
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commercially or noncommercially. Secondarily, this License preserves for the
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author and publisher a way to get credit for their work, while not being
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considered responsible for modifications made by others.
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This License is a kind of "copyleft", which means that derivative works of
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the document must themselves be free in the same sense. It complements the
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GNU General Public License, which is a copyleft license designed for free
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software.
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We have designed this License in order to use it for manuals for free
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software, because free software needs free documentation: a free program
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should come with manuals providing the same freedoms that the software does.
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But this License is not limited to software manuals; it can be used for any
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textual work, regardless of subject matter or whether it is published as a
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printed book. We recommend this License principally for works whose purpose
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is instruction or reference.
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-----------------------------------------------------------------------------
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3.3. APPLICABILITY AND DEFINITIONS
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This License applies to any manual or other work that contains a notice
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placed by the copyright holder saying it can be distributed under the terms
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of this License. The "Document", below, refers to any such manual or work.
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Any member of the public is a licensee, and is addressed as "you".
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A "Modified Version" of the Document means any work containing the Document
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or a portion of it, either copied verbatim, or with modifications and/or
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translated into another language.
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A "Secondary Section" is a named appendix or a front-matter section of the
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Document that deals exclusively with the relationship of the publishers or
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authors of the Document to the Document's overall subject (or to related
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matters) and contains nothing that could fall directly within that overall
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a Secondary Section may not explain any mathematics.) The relationship could
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be a matter of historical connection with the subject or with related
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The "Invariant Sections" are certain Secondary Sections whose titles are
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designated, as being those of Invariant Sections, in the notice that says
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that the Document is released under this License.
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The "Cover Texts" are certain short passages of text that are listed, as
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Front-Cover Texts or Back-Cover Texts, in the notice that says that the
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Document is released under this License.
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A "Transparent" copy of the Document means a machine-readable copy,
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represented in a format whose specification is available to the general
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drawing editor, and that is suitable for input to text formatters or for
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automatic translation to a variety of formats suitable for input to text
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formatters. A copy made in an otherwise Transparent file format whose markup
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has been designed to thwart or discourage subsequent modification by readers
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is not Transparent. A copy that is not "Transparent" is called "Opaque".
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Examples of suitable formats for Transparent copies include plain ASCII
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without markup, Texinfo input format, LaTeX input format, SGML or XML using a
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publicly available DTD, and standard-conforming simple HTML designed for
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formats that can be read and edited only by proprietary word processors, SGML
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or XML for which the DTD and/or processing tools are not generally available,
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purposes only.
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The "Title Page" means, for a printed book, the title page itself, plus such
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requires to appear in the title page. For works in formats which do not have
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any title page as such, "Title Page" means the text near the most prominent
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appearance of the work's title, preceding the beginning of the body of the
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text.
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-----------------------------------------------------------------------------
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3.4. VERBATIM COPYING
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You may copy and distribute the Document in any medium, either commercially
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or noncommercially, provided that this License, the copyright notices, and
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the license notice saying this License applies to the Document are reproduced
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in all copies, and that you add no other conditions whatsoever to those of
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this License. You may not use technical measures to obstruct or control the
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reading or further copying of the copies you make or distribute. However, you
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may accept compensation in exchange for copies. If you distribute a large
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enough number of copies you must also follow the conditions in section 3.
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You may also lend copies, under the same conditions stated above, and you may
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publicly display copies.
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-----------------------------------------------------------------------------
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3.5. COPYING IN QUANTITY
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If you publish printed copies of the Document numbering more than 100, and
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the Document's license notice requires Cover Texts, you must enclose the
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copies in covers that carry, clearly and legibly, all these Cover Texts:
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Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover.
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Both covers must also clearly and legibly identify you as the publisher of
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these copies. The front cover must present the full title with all words of
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the title equally prominent and visible. You may add other material on the
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covers in addition. Copying with changes limited to the covers, as long as
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they preserve the title of the Document and satisfy these conditions, can be
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treated as verbatim copying in other respects.
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If the required texts for either cover are too voluminous to fit legibly, you
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should put the first ones listed (as many as fit reasonably) on the actual
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cover, and continue the rest onto adjacent pages.
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If you publish or distribute Opaque copies of the Document numbering more
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than 100, you must either include a machine-readable Transparent copy along
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with each Opaque copy, or state in or with each Opaque copy a
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publicly-accessible computer-network location containing a complete
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Transparent copy of the Document, free of added material, which the general
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distribute an Opaque copy (directly or through your agents or retailers) of
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It is requested, but not required, that you contact the authors of the
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Document well before redistributing any large number of copies, to give them
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a chance to provide you with an updated version of the Document.
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-----------------------------------------------------------------------------
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3.6. MODIFICATIONS
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You may copy and distribute a Modified Version of the Document under the
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conditions of sections 2 and 3 above, provided that you release the Modified
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Version under precisely this License, with the Modified Version filling the
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role of the Document, thus licensing distribution and modification of the
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Modified Version to whoever possesses a copy of it. In addition, you must do
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these things in the Modified Version:
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A. Use in the Title Page (and on the covers, if any) a title distinct from
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that of the Document, and from those of previous versions (which should,
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if there were any, be listed in the History section of the Document). You
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may use the same title as a previous version if the original publisher of
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that version gives permission.
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B. List on the Title Page, as authors, one or more persons or entities
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responsible for authorship of the modifications in the Modified Version,
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together with at least five of the principal authors of the Document (all
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of its principal authors, if it has less than five).
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C. State on the Title page the name of the publisher of the Modified
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Version, as the publisher.
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D. Preserve all the copyright notices of the Document.
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E. Add an appropriate copyright notice for your modifications adjacent to
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the other copyright notices.
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F. Include, immediately after the copyright notices, a license notice giving
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the public permission to use the Modified Version under the terms of this
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License, in the form shown in the Addendum below.
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G. Preserve in that license notice the full lists of Invariant Sections and
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required Cover Texts given in the Document's license notice.
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H. Include an unaltered copy of this License.
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I. Preserve the section entitled "History", and its title, and add to it an
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item stating at least the title, year, new authors, and publisher of the
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Modified Version as given on the Title Page. If there is no section
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entitled "History" in the Document, create one stating the title, year,
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authors, and publisher of the Document as given on its Title Page, then
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add an item describing the Modified Version as stated in the previous
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sentence.
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J. Preserve the network location, if any, given in the Document for public
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access to a Transparent copy of the Document, and likewise the network
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locations given in the Document for previous versions it was based on.
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These may be placed in the "History" section. You may omit a network
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location for a work that was published at least four years before the
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Document itself, or if the original publisher of the version it refers to
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gives permission.
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K. In any section entitled "Acknowledgements" or "Dedications", preserve the
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section's title, and preserve in the section all the substance and tone
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of each of the contributor acknowledgements and/or dedications given
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therein.
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L. Preserve all the Invariant Sections of the Document, unaltered in their
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text and in their titles. Section numbers or the equivalent are not
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considered part of the section titles.
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M. Delete any section entitled "Endorsements". Such a section may not be
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included in the Modified Version.
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N. Do not retitle any existing section as "Endorsements" or to conflict in
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title with any Invariant Section.
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If the Modified Version includes new front-matter sections or appendices that
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||
qualify as Secondary Sections and contain no material copied from the
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Document, you may at your option designate some or all of these sections as
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invariant. To do this, add their titles to the list of Invariant Sections in
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the Modified Version's license notice. These titles must be distinct from any
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||
other section titles.
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||
|
||
You may add a section entitled "Endorsements", provided it contains nothing
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but endorsements of your Modified Version by various parties--for example,
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statements of peer review or that the text has been approved by an
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organization as the authoritative definition of a standard.
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||
|
||
You may add a passage of up to five words as a Front-Cover Text, and a
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||
passage of up to 25 words as a Back-Cover Text, to the end of the list of
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||
Cover Texts in the Modified Version. Only one passage of Front-Cover Text and
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one of Back-Cover Text may be added by (or through arrangements made by) any
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one entity. If the Document already includes a cover text for the same cover,
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previously added by you or by arrangement made by the same entity you are
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acting on behalf of, you may not add another; but you may replace the old
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one, on explicit permission from the previous publisher that added the old
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one.
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||
|
||
The author(s) and publisher(s) of the Document do not by this License give
|
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permission to use their names for publicity for or to assert or imply
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||
endorsement of any Modified Version.
|
||
-----------------------------------------------------------------------------
|
||
|
||
3.7. 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.
|
||
|
||
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."
|
||
-----------------------------------------------------------------------------
|
||
|
||
3.8. 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.
|
||
-----------------------------------------------------------------------------
|
||
|
||
3.9. 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, 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.
|
||
-----------------------------------------------------------------------------
|
||
|
||
3.10. 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 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.
|
||
-----------------------------------------------------------------------------
|
||
|
||
3.11. 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.
|
||
-----------------------------------------------------------------------------
|
||
|
||
3.12. 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/] 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.
|
||
-----------------------------------------------------------------------------
|
||
|
||
3.13. 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.
|