Simplify instructions for checking cvs2svn out of Subversion.
[cvs2svn.git] / www / cvs2git.html
1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
2 "">
3 <html xmlns="">
4 <head>
5 <style type="text/css"> /* <![CDATA[ */
6 @import "tigris-branding/css/tigris.css";
7 @import "tigris-branding/css/inst.css";
8 /* ]]> */</style>
9 <link rel="stylesheet" type="text/css" media="print"
10 href="tigris-branding/css/print.css"/>
11 <script type="text/javascript" src="tigris-branding/scripts/tigris.js"></script>
12 <title>cvs2git Documentation</title>
13 </head>
15 <body id="bodycol">
16 <div class="app">
18 <h1>cvs2git</h1>
20 <h2>Index</h2>
22 <ul>
24 <li><a href="#intro">Introduction</a></li>
26 <li><a href="#reqs">Requirements</a></li>
28 <li><a href="#status">Development status</a></li>
30 <li><a href="#docs">Documentation</a></li>
32 <li><a href="#usage">Usage</a></li>
34 </ul>
36 <hr />
38 <h2><a name="intro">Introduction</a></h2>
40 <p>cvs2svn/cvs2git is a tool that can be used to migrate CVS
41 repositories to newer version control tools, including <a
42 href="">git</a>. git is a distributed version
43 control system most famous for being used for Linux kernel
44 development. The program used to convert to git, called cvs2git, is
45 distributed as part of the cvs2svn project.</p>
47 <p><strong>If you are reading this documentation on the <a
48 href="">cvs2svn website</a>, then please be
49 aware that it describes the current trunk version of cvs2svn, which
50 may be different than the most recent released version. Please refer
51 to the documentation that was included with your version of cvs2svn.
52 </strong></p>
54 <p>Conversion to git was added in release 2.1 of cvs2svn and has
55 improved significantly since then. Please make sure you are using an
56 up-to-date version of cvs2svn--perhaps even the development trunk
57 version.</p>
60 <h2><a name="reqs">Requirements</a></h2>
62 <p>cvs2git requires the following:</p>
64 <ul>
66 <li>Direct (filesystem) access to a copy of the CVS repository that
67 you want to convert. cvs2git parses the files in the CVS
68 repository directly, so it is not enough to have remote CVS
69 access. See the <a href="faq.html#repoaccess">FAQ</a> for more
70 information and a possible workaround.</li>
72 <li>Python 2, version 2.4 or later. See <a
73 href=""></a>.
74 (cvs2git does <strong>not</strong> work with Python 3.x.)</li>
76 <li>If you use the <tt>--use-rcs</tt> option, then RCS's `co'
77 program is required. The RCS home page is
78 <a href=""
79 ></a>.
80 See the <a href="cvs2svn.html#use-rcs"><tt>--use-rcs</tt> flag</a> for more
81 details.</li>
83 <li>If you use the <tt>--use-cvs</tt> option, then the `cvs' command
84 is required. The CVS home page is
85 <a href=""></a>.
86 See the <a href="cvs2svn.html#use-cvs"><tt>--use-cvs</tt> flag</a> for more
87 details.</li>
89 <li> Git version or later (earlier versions have a bug in
90 "git fast-import" that prevent them from loading the files
91 generated by cvs2git).</li>
93 </ul>
96 <h2><a name="status">Development status</a></h2>
98 <p>Most of the work of converting a repository from CVS to a more
99 modern version control system is inferring the most likely history
100 given the incomplete information that CVS records. cvs2svn has a long
101 history of making sense of even the most convoluted CVS repositories,
102 and cvs2git uses this same machinery. Therefore, cvs2git inherits the
103 robustness and many of the <a href="features.html">features of
104 cvs2svn</a>. cvs2svn can convert just about every CVS repository we
105 have ever seen, and includes a plethora of options for customizing
106 your conversion.</p>
108 <p>The output of cvs2git is one or more dump files that can be
109 imported into git using the excellent <a
110 href="
111 fast-import.html">git fast-import</a> tool.</p>
113 <p>Although cvs2git is considerably newer than cvs2svn, and much less
114 well tested, it is believed that cvs2git can (cautiously) be used for
115 production conversions. If you use cvs2git, please let us know how it
116 worked for you!</p>
119 <h2><a name="limitations">cvs2git limitations</a></h2>
121 <p>cvs2git still has many limitations compared to cvs2svn. The main
122 cvs2svn developer has limited git experience and very limited time, so
123 <strong>help would be much appreciated!</strong> Some of these missing
124 features would be pretty easy to program, and I'd be happy to help you
125 get started.</p>
127 <ul>
129 <li>The cvs2git documentation is still not as complete as that for
130 cvs2svn. See <a href="#docs">below</a> for more references.</li>
132 <li>Differences between CVS and git branch/tag models: CVS allows a
133 branch or tag to be created from arbitrary combinations of source
134 revisions from multiple source branches. It even allows file
135 revisions that were never contemporaneous to be added to a single
136 branch/tag. Git, on the other hand, only allows the full source
137 tree, as it existed at some instant in the history, to be branched
138 or tagged as a unit. Moreover, the ancestry of a git revision
139 makes <a
140 href="">implications
141 about the contents of that revision</a>. This difference means
142 that it is fundamentally impossible to represent an arbitrary CVS
143 history in a git repository 100% faithfully. cvs2git uses the
144 following workarounds:
146 <ul>
148 <li>cvs2git tries to create a branch from a single source, but
149 if it can't figure out how to, it creates the branch using a
150 "merge" from multiple source branches. In pathological
151 situations, the number of merge sources for a branch can be
152 arbitrarily large. The resulting history implies that
153 whenever any file was added to a branch, the <em>entire</em>
154 source branch was merged into the destination branch, which is
155 clearly incorrect. (The alternative, to omit the merge, would
156 discard the information that <em>some</em> content was moved
157 from one branch to the other.)</li>
159 <li>If cvs2git cannot determine that a CVS tag can be created
160 from a single revision, then it creates a <a
161 href="">tag
162 fixup branch</a> named <tt>TAG.FIXUP</tt>, then tags this
163 branch. (This is a necessary workaround for the fact that git
164 only allows existing revisions to be tagged.) The
165 <tt>TAG.FIXUP</tt> branch is created as a merge between all of
166 the branches that contain file revisions included in the tag,
167 which involves the same tradeoff described above for branches.
168 The <tt>TAG.FIXUP</tt> branch is cleared at the end of the
169 conversion, but (due to a technical limitation of the git
170 fast-import file format) not deleted. There are some
171 situations when a tag <em>could</em> be created from a single
172 revision, but cvs2git does not realize it and creates a
173 superfluous tag fixup branch. It is possible to delete
174 superfluous tag fixup branches after the conversion by running
175 the <tt>contrib/</tt> script within the
176 resulting git repository.</li>
178 </ul>
180 </li>
182 <li>There are no checks that CVS branch and tag names are legal git
183 names. There are probably other git constraints that should also
184 be checked.</li>
186 <li>The data that should be fed to git fast-import are written to
187 two files, which have to be loaded into git fast-import manually.
188 These files might grow to very large size. It would be nice to
189 add an option to invoke git fast-import automatically and pipe the
190 output directly into git fast-import; this should also speed up
191 the conversion.</li>
193 <li>Only single projects can be converted at a time. Given the way
194 git is typically used, I don't think that this is a significant
195 limitation.</li>
197 <li>cvs2git is rather slow when started with the <tt>--use-rcs</tt>
198 or <tt>--use-cvs</tt> options. It is much faster when started
199 with the <tt>--use-external-blob-generator</tt> option, but that
200 option is still experimental.</li>
202 <li>The cvs2svn test suite does not include meaningful tests of git
203 output.</li>
205 <li>cvs2git makes no attempt to convert <tt>.cvsignore</tt> files
206 into <tt>.gitignore</tt> files.</li>
208 <li>cvs2git, like cvs2svn, does not support incremental conversion
209 (i.e., tracking a live CVS repository). However, at least one
210 person has documented a <a
211 href="">possible
212 workaround</a>.</li>
214 </ul>
217 <h2><a name="docs">Documentation</a></h2>
219 <p>There is some documentation specific to cvs2git, and much of the
220 cvs2svn documentation also applies fairly straightforwardly to
221 cvs2git. See the following sources:</p>
223 <ul>
225 <li>This document.</li>
227 <li>The output of <tt>cvs2git --help</tt>.</li>
229 <li>The cvs2git man page. If the man page is not installed on your
230 Unix-like system, you can view it by typing a command like
231 <tt>cvs2git --man | groff -man -Tascii | less</tt>.</li>
233 <li><a href="cvs2svn.html#intro">The cvs2svn documentation</a> and
234 <a href="faq.html">the cvs2svn FAQ</a>, which contain much general
235 discussion and describe many features that can also be used for
236 cvs2git.</li>
238 <li><tt>cvs2git-example.options</tt> in the cvs2svn source tree,
239 which is an example of an options file that can be used to
240 configure a cvs2git conversion. The file is extensively
241 documented.</li>
243 <li>The cvs2svn mailing lists, IRC channel, etc., as described in <a
244 href="faq.html#gettinghelp">the cvs2svn FAQ</a>.</li>
246 </ul>
249 <h2><a name="usage">Usage</a></h2>
251 <p>This section outlines the steps needed to convert a CVS repository
252 to git using cvs2git.</p>
254 <ol>
256 <li>Be sure that you have the <a href="#reqs">requirements</a>,
257 including either RCS or CVS (used to read revision contents from
258 the CVS repository).</li>
260 <li>Obtain a copy of cvs2svn/cvs2git version 2.1 or newer. It is
261 recommended that you use the most recent version available, or
262 even the development version.
264 <ul>
266 <li>To install cvs2svn from a <a
267 href="">tarball</a>,
268 simply unpack the tarball into a directory on your conversion
269 computer (cvs2git can be run directly from this
270 directory).</li>
272 <li>
274 <p>To check out the current trunk version of cvs2svn, make
275 sure that you have Subversion installed and then run:</p>
277 <pre>
278 svn co --username=guest --password="" cvs2svn-trunk
279 cd cvs2svn-trunk
280 make man # If you want to create manpages for the main programs
281 make check # ...optional
282 </pre>
284 <p>Please note that the test suite includes tests that are
285 marked "XFAIL" (expected failure); these are known and are
286 not considered serious problems.</p>
288 </li>
290 </ul>
292 </li>
294 <li>
296 Configure cvs2git for your conversion. This can be done via
297 command-line options or via an options file:
299 <ul>
301 <li>The command-line options for running cvs2git are documented
302 in the cvs2git man page and in the output of <tt>cvs2git
303 --help</tt>.</li>
305 <li>
307 <p>The more flexible <a
308 href="cvs2svn.html#cmd-vs-options">options-file method</a>
309 requires you to create an options file, then start cvs2git
310 with</p>
312 <pre>
313 cvs2git --options=OPTIONS-FILE
314 </pre>
316 <p>Use <tt>cvs2git-example.options</tt> in the cvs2svn source
317 tree as your starting point; the file contains lots of
318 documentation.</p>
320 </li>
322 </ul>
324 </li>
326 <li>
328 <p>Run cvs2git. This creates two output files in <a
329 href="">git
330 fast-import</a> format. The names of these files are specified by
331 your options file or command-line arguments. In the example,
332 these files are named <tt>cvs2svn-tmp/git-blob.dat</tt> and
333 <tt>cvs2svn-tmp/git-dump.dat</tt>.</p>
335 </li>
337 <li>
339 <p>Initialize a git repository, and load the dump files using
340 git fast-import:</p>
342 <pre>
343 git init
344 git fast-import --export-marks=cvs2svn-tmp/git-marks.dat &lt; cvs2svn-tmp/git-blob.dat
345 git fast-import --import-marks=cvs2svn-tmp/git-marks.dat &lt; cvs2svn-tmp/git-dump.dat
346 </pre>
348 <p>This can, of course, be shortened to:</p>
350 <pre>
351 git init
352 cat cvs2svn-tmp/git-blob.dat cvs2svn-tmp/git-dump.dat | git fast-import
353 </pre>
355 </li>
357 <li>If you want to get rid of unnecessary tag fixup branches, then
358 run the <tt>contrib/</tt> script from within the
359 git repository.</li>
361 </ol>
363 <p>Feedback would be much appreciated, including reports of success
364 using cvs2git. Please send comments, bug reports, and patches to
365 the <a
366 href="">cvs2svn
367 mailing lists</a>.</p>
369 </div>
370 </body>
371 </html>