distributed version control systems.


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DVC Intro

       Copyright (C) 2007 - 2012 Stephen Leake
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, with no Front-Cover Texts, and with no
       Back-Cover Texts. A copy of the license is included in the section
       entitled ``GNU Free Documentation License''.

--- The Detailed Node Listing ---

Overview

Invoking

Key bindings

Common Errors and Solutions


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1 Overview

DVC is a common interface to several extremely powerful and flexible version control systems, such as Gnu arch, monotone, bzr, and others (known as 'backends' to DVC).

DVC provides the same (or at least similar) user interface for each backend, making it easier to use multiple backends in related projects. It also automates some tasks, and provides guidance to the user as to what needs to be done.

DVC is not included with the standard Gnu emacs distribution. It is provided in source form via a bzr repository (see Installing).

If you are not already familiar with version control systems, please read Basic DVC.

One of the most important features of the DVC user interface is that it identifies what files in a project need attention of some sort; you have changed them in your working directory, or someone else has changed them in the repository, or they've been deleted or are new, etc. DVC presents a list of all such files, and makes it easy to see what needs to be done for each file.

When committing files, ediff is used to allow reviewing the changes, so an appropriate change comment can be written.

DVC replaces the command-line interface to the backends for the most common operations, but it is still necessary to use the command line at times. Creating a repository, starting a project in a repository, and managing branches require command line operations.

This manual describes the DVC user interface, and gives examples of some required command line operations, using the monotone backend.

It also describes some DVC extensions that are specific to the monotone backend.


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1.1 Basic DVC

Here we give a brief introduction to general concepts of distributed version control systems, focusing on the concepts that are needed to use DVC, and providing common terminology.

Each backend will have its own documentation, and terminology that differs from this. The terms here are taken mostly from the monotone backend.

Let's start with some definitions:

workspace
Each user has a workspace, containing a copy of the files she is working on. This is typically a directory tree. In the root directory of the tree there is typically a directory containing backend control files, used only by the backend.
database
The database stores copies of all files in the workspace (and typically more than one workspace), together with all of the change history and other meta-information. The database is never edited directly; only the backends modify it.
local database
A database on the user's machine. This database is used to control all workspaces on the user's machine.
remote database
A database on a remote machine. This may be another user's local database, or a central database set up specifically for sharing files. The user interacts with the remote database in order to retrieve other user's files, or deliver files to them.
revision
The state of the entire workspace, usually including the set of changes to the workspace that transform it from the previous revision. Most operations on the database involve revisions, and all changes to files are part of a revision.
branch
A label for distinct trees of revisions. There are two main uses for branches; parallel development on a single project, and completely separate projects. Branches of a single project are typically merged back together (this is called “propagating”), while completely separate projects are not.

A database can store any number of branches.

heads
The revisions that are the leaves of the history tree on a single branch. In monotone, there can be any number of heads on a branch (see Merging).
merge
The process of combining multiple heads of a branch into one head. This can encounter conflicts that require user resolution; see Merging.
propagate
One branch can be “propagated” to another. This is a form of merging; it merges all the changes from one branch into another, starting from their common ancestor (which is usually the previous propagate between the two branches).

This is how changes in a development branch are promoted to the main branch.

Since propagating is a form of merging, it can encounter all of the same conflicts that merging can.

*dvc-status* buffer
A main user interface buffer. It shows all files in the workspace that need attention. Single keystrokes invoke various operations. See Status Display, for more details.

The name of the buffer is not literally *dvc-status*; instead, dvc is replaced by the backend name; xmtn for monotone, bzr for bzr, etc. But in this document, we will use the name *dvc-status*.

*dvc-diff* buffer
Another main user interface buffer. It shows the files changed in a particular revision, together with the diffs of the changes. Single keystrokes invoke various operations.

Users edit files in their workspace, then use DVC to synchronize the workspace with the local database. Later, they use the command line to synchronize their local database with a remote database. This allows each user to make changes locally but still under change control, without affecting other users until they each choose to synchronize.


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1.2 Compare to CVS

Since many people are familiar with the CVS version control system, we compare that with DVC, and monotone in particular.

In CVS, each file is committed separately; in DVC, all files in a workspace are committed together. This makes sure that all changes that are related are committed together.

This means the commit log message mentions all files that have changes; it is a much longer message, but there are fewer of them, and the message can more easily describe changes that affect more than one file.

In CVS, you must always have access to the remote server. In DVC, you work with a local database, then separately sync that database with a remote server. Thus DVC is useful when not on a network; monotone can even sync via USB disk rather than a network connection.

This means there are two steps to syncing a workspace with the central server, which can be annoying. On the other hand, the sync process syncs all projects in the database at once; with monotone, it lets you know what projects have changes.

Otherwise the primary Emacs interface to CVS and DVC are very similar, although DVC has many secondary interfaces that CVS does not have.


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2 Installing

Install bzr; see http://bazaar.canonical.com/en/.

Retrieve the DCV source; see https://gna.org/projects/dvc#options for general information.

In a bash shell:

     cd ~
     bzr get http://bzr.xsteve.at/dvc/
     cd ~/dvc
     autoconf
     ./configure
     make

In your .emacs, add (load-file (expand-file-name "~/dvc/dvc-load.el"))


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3 Invoking

Before invoking DVC, you may want to ensure that the local database is synchronized with the central database, via a backend-specific command line.

You typically invoke DVC with the Emacs command dvc-status or dvc-diff. This prompts for a workspace; it should be the top level directory in your working directory tree.

You can also create shortcuts in text files to invoke dvc:

     (dvc-status (expand-file-name "~/dvc"))
     (dvc-diff nil (expand-file-name "~/dvc"))

These can be executed with <C-x C-e>, and are a handy way of keeping track of several workspaces.

dvc-status or dvc-diff run the corresponding backend command, comparing the workspace against the local database, and presenting the information in the *dvc-status* or *dvc-diff* buffer.

For monotone, there are higher-level starting points:

xmtn-status-one
Summarizes the status of one workspace.
xmtn-status-multiple
Similar to xmtn-status-one, but shows all workspaces immediately under a root directory.
xmtn-propagate-one
Supervises propagating one workspace.
xmtn-propagate-multiple
Supervises propagating several workspaces.
xmtn-sync-review
Reviews saved output of a command-line mtn automate sync, displays branches that have been transferred. This is useful for syncs that take a long time, because the command-line displays progress tickers.


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3.1 xmtn-status-one

Summarizes the status of one workspace, in a xmtn-multi-status buffer. The branch name is shown, followed by possible appropriate actions. As each action is performed, it is replaced by the next action, until there are none left.

Similarly, xmtn-status-multiple shows the status of all workspaces immediately under a root directory.

Actions are invoked with <M-d>.

The possible actions are:

need-refresh
Shown while the backend is computing, or the user is performing operations in an associated *xmtn-multi-status* buffer.
commit
Open an *xmtn-status* buffer to commit changes.
resolve conflicts
Open an *xmtn-conflicts* buffer to resolve conflicts; see Merging.
show heads
Open an *xmtn-revlist* buffer to show the current head revisions.
merge
Perform the merge, using the conflict resolutions.
update
Update the workspace to the current head revision (must be merged).
update preview
Open an *xmtn-revlist* buffer to review the revisions that will be included in the next update.
update review
Open an *xmtn-revlist* buffer to review the revisions that were included in the most recent update.
ignore local changes
Don't show commit.
refresh
Recompute the *xmtn-multi-status* display.
clean/delete
Delete conflicts and conflict resolution files, and delete the workspace from the display.


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3.2 xmtn-propagate-one

xmtn-propagate-one supervises the process of propagating from one workspace to another, in an xmtn-propagate buffer.

The display shows one source and destination branch pair, and possible appropriate actions. As each action is performed, it is replaced by the next action, until there are none left.

Similarly, xmtn-propagate-multiple supervises the propagation of all workspaces immediately under two root directories. This is useful when several related projects branch together.

In the list of actions, “from” stands for the name of the source branch, “to” the name of the destination branch.

Actions are invoked with <M-d>.

The possible actions are:

status ``from''
status ``to''
Start an xmtn-multi-status buffer for the specified workspace, to allow commit, update preview, or merge with conflict resolution.
update ``to''
Update the specified workspace to the current head revision (must be merged). This bypasses the xmtn-multi-status buffer, and therefore does not provide for update preview. It does allow for update review.
ignore local changes ``from''
ignore local changes ``to''
Don't show need commit; assume the workspace is committed. Useful when you know that any local changes won't interfere with the propagate.
resolve conflicts
Open an *xmtn-conflicts* buffer in the destination workspace to resolve propagate conflicts; see Merging.
propagate
Propagate the branch pair, using the conflict resolutions.
refresh
Recompute the display. If prefixed with <C-u>, force examining workspaces for local changes.
clean/delete
Delete conflicts and conflict resolution files, and delete the workspace from the display.


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3.3 xmtn-sync-review

xmtn-sync-review supervises the process of updating local workspaces after a command line operation that synchronizes the local and remote databases.

The command line operation should redirect stdout to ~/.dvc/sync.basic_io. Most users will want to define shell functions to invoke common syncs. For example:

         mtn --db ~/monotone-dbs/gds.db automate sync --ticker=count "ssh:user@host/gds.db?*" >> ~/.dvc/sync.basic_io

The xmtn-sync-review display shows each branch that was transferred, with a count of how many revisions were sent and received.

The user may set the variable xmtn-sync-sort to a function that indicates how to order the branches in the display.

Actions on branches are invoked with <M-d>.

The possible branch actions are:

status
Start an xmtn-multi-status buffer for the workspace assoicated with the specified branch, to allow commit, update preview, update followed by update review, or merge with conflict resolution.

The user may set the variable xmtn-sync-guess-workspace to a function that returns a workspace given a branch. Otherwise, the user is prompted for the workspace location; the location is cached for future use.

update
Start an xmtn-multi-status buffer for the workspace assoicated with the specified branch, then perform update (if appropriate). This is often convenient when you know the workspace has no local changes.
brief
Show the first line of the changelog for each revision received.
full
Show the complete changelog for each revision received.
clean
Delete the branch from the display.

Branches that are not cleaned are cached; they will reappear the next time xmtn-sync-review is run.

In addition, there are global actions:

next
Move to the next branch
prev
Move to the previous branch
save-quit
Save the displayed branches, quit.
save
Save the displayed branches.


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4 Status Display

After invoking dvc-status, you are presented with the *dvc-status* buffer.

The detailed format differs depending on the backend. This presentation is close to the bzr and mtn formats.

The buffer contains a header, such as:

     Status for c:/Projects/GDS/common/main/:
       base revision : e946839c833b15e6bf12bd1536764e1106c41924
       branch        : common.main
       branch is merged
       base revision is a head revision

The last two lines are important; either may have “not” in it.

If the branch is not merged, it must be merged before an update can be done; see Merging. However, commits can be done when the branch is not merged; this allows saving work before attempting the merge.

If the base revision is not a head revision, there are updates that need to be applied to the workspace. The updates may be reviewed first using <M m>; they may be applied using <M u>.

In the main body of the buffer, there is one line for each file in the workspace that needs attention. For example:

      * modified      hardware/gds-hardware-pmrd_wrapper.adb
        unknown       build/ip1k110_quartus/serv_req_info.txt
      E modified      hardware/test/test_hardware-one_harness.adb

Each line has three fields:

Mark
Either blank (not marked), '*' (marked), or 'E' (excluded). Most commands can apply to a group of marked files, but some cannot (they warn if a group is marked).

Excluded files are under configuration management, but are excluded from commits. This is used for files that each user modifies, such as development test drivers.

Status
A phrase indicating the status of the file; see the table below.
File name
Gives the file name of the working file, with a path relative to the root directory.

In addition, some files will have extra status information that appears on the next line, indented.

The following table defines each status phrase, and gives the set of actions that can be taken for each. The action shown is from the DVC menu; the equivalent key is also given.

Other actions (such as commit) apply to all files; they are discussed later.

`Added'
Working file has been added, but not committed.
`<r> Delete'
Remove the file from the workspace, do not commit it. Do this if you've changed your mind.

`Conflict'
A conflict was detected while merging. The same lines have been edited differently by different people.

This status does not appear with the monotone back-end.

`<<enter>> Edit the file.'
Either resolve the conflict manually, or use M-x smerge-ediff. Execute M-x dvc-resolve when finished to inform the back-end that the conflict is resolved.
`<U> Revert'
Delete the working copy, replace it with the database copy. Do this if you decide the changes are not correct.

`Deleted'
Working file has been marked for deletion, but not committed.
`<a> Add'
Undo the removal.

`Ignored'
Working file is ignored by the back-end. Files with this status are not typically shown - ignored files are ignored by DVC as well. They can be enabled by setting dvc-status-display-ignored to nil.
`<# e>'
Edit the back-end ignore file.

`Known'
Working file is known to the back-end, and unchanged. Files with this status are not typically shown. They can be enabled by setting dvc-status-display-known to nil. There are no appropriate actions.
`Missing'
A previously known file has been deleted from the workspace, but not marked for deletion.
<U> Revert Restore the file to the workspace from the database.
`<r> Delete'
Mark the file for deletion.

`Modified'
A changed file in the workspace.
`<e> ediff'
Review differences and collect a change comment.
`<U> Revert'
Delete the working copy, replace it with the database copy. Do this if you decide your changes are not correct.

`Rename-source'
Working file has been marked as renamed but not committed. No appropriate actions.
`Rename-target'
Working file has been marked as renamed but not committed. No appropriate actions.
`Unknown'
Working file is unknown.
`<a> Add'
The file is a new source file; add it to the current revision. This will change the status to 'Added'.
`<i> Ignore'
The file is an output file of some sort (ie object file, test output). Ignore it in all future DVC sessions.
`<I> Ignore extension in dir'
Ignore all files with this extension in this directory.
`<M-I> Ignore extension'
Ignore all files with this extension in all directories.
`<r> Delete'
The file is a scratch file, or was created by mistake. Remove it from the workspace.

Changes are committed all at once; the set of changes to the entire workspace is called a “revision”. <c> opens the *dvc-log-edit* buffer, where you can write a change comment. Then <C-c C-c> commits all changes.

The key <M-d> invokes a function called “Do the Right Thing”. If there is only a single choice (or an extremely common choice) in the table above, it does that action. Otherwise, it presents a short list of the actions, in the message buffer, reminding the user of the appropriate options. Note that <M-d> means meta-d (alt-d on most PC keyboards))


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5 Key bindings

Here is a summary of the most useful key bindings in the various buffers associated with DVC.


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5.1 status buffer keys

In a *dvc-status* buffer:

<M-d>
Do the right thing for the current file.
<c>
Open a *dvc-log-edit* buffer to accumulate comments for a commit.
<M m>
Show missing revisions; changes that will be applied by update.
<M M>
Merge current heads; see Merging.
<M u>
Update to the current head.
<R>
Rename a missing to an unknown file. The two files must be marked first, and they must be the only files marked. This operation is just bookkeeping; it does not affect the actual disk files.
<t>
Create an entry in the *dvc-log-edit* for the current diff.


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5.2 Ediff keys

In an Ediff control buffer (the small window with Ediff in the title bar):

<a>
Copy from buffer A to buffer B.
<b>
Copy from buffer B to buffer A.
<n>
Move to next diff.
<p>
Move to previous diff.
<q>
Quit Ediff.
<t>
Create an entry in the *dvc-log-edit* for the current diff.
<$$>
Focus on conflicts in a merge.
<?>
Show the help summary for Ediff. <?> hides it again.


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5.3 log edit keys

In the *dvc-log-edit* buffer:

<C-c C-c>
Commit. Note that this is the only way to actually commit.


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5.4 DVC log keys

In a *xmtn-log* buffer:

<n>
move to the next revision
<p>
move to the previous revision
<=>
show a diff of the changes in a single revision
<C-=>
show a diff between the revision and the workspace


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5.5 DVC diff keys

In a *dvc-diff* buffer:

<e>
show ediff for current file
<j>
jump between file list and diff hunks
<n>
move to the next diff hunk
<p>
move to the previous diff hunk


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5.6 mtn conflicts keys

In a *xmtn-conflicts* buffer:

<C>
Delete conflicts file and any resolution files.
<c>
Clear the current resolution, so you can specify a different one.
<n>
Move to the next conflict.
<N>
Move to the next unresolved conflict.
<p>
Move to the previous conflict.
<P>
Move to the previous unresolved conflict.
<q>
Quit the *xmtn-conflicts* buffer. The conflicts file and associated resolution files are saved.
<r>
Specify a resolution for the current conflict. This prompts with a choice of resolutions appropriate for the current conflict; select the appropriate resolution by number. See Merging, for information on the possible resolutions.
<M-d>
Same as <r>


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6 Previewing updates

To preview updates before applying them to your workspace, use the dvc-missing command; it's on the status buffer menu at DVC | Merge/Update | show missing.

dvc-missing can also be invoked via the Emacs command line (<M-x>); that prompts for a local tree.

Invoking dvc-missing brings up an *dvc-log* window, showing revisions that are in your local database but not yet applied to the workspace.

The revisions are listed oldest first.

You can view the changes made in a single revision, or from that revision to the current workspace.

See See Log edit keys, for key bindings.

<=> and <C-=> bring up a *dvc-diff* buffer for the revision selected. The diffs are shown in Gnu diff format; all files in one *dvc-diff* buffer. There is a list of the files at the top of the buffer. See See DVC diff keys, for key bindings.

Note that you can also review updates after they have been applied. This is often more useful, because you can edit the workspace file to fix problems caused by the update, or just to see the final state after all revisions have been applied.


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7 Merging

Monotone allows multiple people to each commit to their local database. Then when the databases are synced, there are multiple heads for the branch; one head for each developer that commited since the last sync.

These multiple heads must be merged before a local workspace can be updated to the head of the branch; there must be only one head to update to. The monotone command line allows updating to one head of an unmerged branch, but DVC does not support this.

When the changes in the different heads are to different files, or to different parts of the same file, monotone can perform the merge itself. However, when there are changes to the same parts of one file, it needs help; this is called a content conflict.

An *xmtn-conflicts* buffer shows all conflicts in a merge or propagate. You can work thru the list one a time, using <M-d> to specify conflict resolutions. The list is saved in a file, so you can come back to it later.

The conflicts that monotone knows how to resolve internally have resolutions of resolved-internal; the others have no resolutions.

The conflicts file and associated resolution files are stored in the monotone bookkeeping area. They must be deleted when you are done with them; use <C C> for that.

<M-d> prompts with a list of appropriate resolutions for the current conflict; select the appropriate resolution by number. The possible resolutions are:

right: drop
left: drop
Resolve one side of a duplicate name conflict by dropping it.
drop
Resolve an orphaned node conflict by dropping it.
right: rename
left: rename
Resolve one side of a duplicate name conflict by specifying a new name.
rename
Resolve an orphaned node conflict by specifying a new name.
right: right file
right: left file
left: right file
left: left file
Resolve one side of a duplicate name conflict by specifying a file.

The other side must be dropped or renamed.

left file
Resolve a content conflict by specifying a file. The file defaults to the current workspace file.
right: keep
left: keep
Resolve one side of a duplicate name conflict by keeping it as is.

The other side must be dropped or renamed.

right: ediff
left: ediff
Resolve one side of a duplicate name conflict by ediff. This brings up an ediff merge of the two files, and saves the result in the resolution file area.

The other side must be dropped or renamed.

ediff
Resolve a content conflict via ediff. This brings up an ediff merge of the two files, and saves the result in the resolution file area.

See See mtn conflicts keys, for a summary of key bindings.


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8 mtn command line

Sometimes, especially over NFS, the Emacs DVC interface can be painfully slow, and it is appropriate to use the mtn command line instead.

Other times, the mtn command line is just simpler.

So we list the most useful mtn commands here. See the monotone command line help or manual for more information.

status
mtn status
commit
mtn commit --message="<message>"

mtn commit --message-file=_MTN/log

rename
mtn rename <file> <new-file>
update
mtn update --move-conflicting-paths


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9 Common Errors and Solutions


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9.1 Attach blocked by unversioned path

Problem: When attempting to update a directory, this warning appears:

     $ mtn update
      ...
     mtn: warning: attach node 2147486644 blocked by unversioned path '<file path>'
     mtn: misuse: 1 workspace conflict

Explanation: "Unversioned path" means the indicated file is not in the current revision, however the file already exists on the disk. The revision you are updating to contains the file, but it can't be updated because it would overwrite the unknown file on the disk

Solution: Delete the indicated files from the disk and retry the update, or specify the --move-conflicting-paths option.


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9.2 Revision id does not match conflict file

Problem: When attempting to propagate from one branch to another, this message appears:

     $ mtn: propagating common.main -> common.work_user
       mtn: [left]  48b675060af47a02bc6f773bd63647726f96cbd5
       mtn: [right] 94ffd0b529dfb44c3ab122fe6c514b5f2e857104
       mtn: misuse: left revision id does not match conflict file

Explanation: It means you have some conflict files left over from a previous propagation or merge.

Solution: In a buffer showing the “from” workspace, run: M-x xmtn-conflicts-clean. Repeat in the “to” workspace, then propagate again.


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Appendix A GNU Free Documentation License

Version 1.2, November 2002
     Copyright © 2000,2001,2002 Free Software Foundation, Inc.
     51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA
     
     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.

    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 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.

  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.