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  12 <title>cvs2git Documentation</title>
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  17
  18 <h1>cvs2git</h1>
  19
  20 <h2>Index</h2>
  21
  22 <ul>
  23
  24   <li><a href="#intro">Introduction</a></li>
  25
  26   <li><a href="#reqs">Requirements</a></li>
  27
  28   <li><a href="#status">Development status</a></li>
  29
  30   <li><a href="#docs">Documentation</a></li>
  31
  32   <li><a href="#usage">Usage</a></li>
  33
  34 </ul>
  35
  36 <hr />
  37
  38 <h2><a name="intro">Introduction</a></h2>
  39
  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="http://git.or.cz/">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>
  46
  47 <p><strong>If you are reading this documentation on the <a
  48 href="http://cvs2svn.tigris.org">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>
  53
  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>
  58
  59
  60 <h2><a name="reqs">Requirements</a></h2>
  61
  62 <p>cvs2git requires the following:</p>
  63
  64 <ul>
  65
  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>
  71
  72   <li>Python 2, version 2.4 or later.  See <a
  73     href="http://www.python.org/">http://www.python.org/</a>.
  74     (cvs2git does <strong>not</strong> work with Python 3.x.)</li>
  75
  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="http://www.cs.purdue.edu/homes/trinkle/RCS/"
  79             >http://www.cs.purdue.edu/homes/trinkle/RCS/</a>.
  80     See the <a href="cvs2svn.html#use-rcs"><tt>--use-rcs</tt> flag</a> for more
  81     details.</li>
  82
  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="http://ccvs.cvshome.org/">http://ccvs.cvshome.org/</a>.
  86     See the <a href="cvs2svn.html#use-cvs"><tt>--use-cvs</tt> flag</a> for more
  87     details.</li>
  88
  89   <li> Git version 1.5.4.4 or later (earlier versions have a bug in
  90     "git fast-import" that prevent them from loading the files
  91     generated by cvs2git).</li>
  92
  93 </ul>
  94
  95
  96 <h2><a name="status">Development status</a></h2>
  97
  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>
 107
 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="http://www.kernel.org/pub/software/scm/git/docs/git
 111 fast-import.html">git fast-import</a> tool.</p>
 112
 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>
 117
 118
 119 <h2><a name="limitations">cvs2git limitations</a></h2>
 120
 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>
 126
 127 <ul>
 128
 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>
 131
 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="http://softwareswirl.blogspot.com/2009/08/git-mercurial-and-bazaarsimplicity.html">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:
 145
 146     <ul>
 147
 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>
 158
 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="http://www.kernel.org/pub/software/scm/git/docs/git-fast-import.html">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/git-move-refs.py</tt> script within the
 176         resulting git repository.</li>
 177
 178     </ul>
 179
 180   </li>
 181
 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>
 185
 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>
 192
 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>
 196
 197   <li>The cvs2svn test suite does not include meaningful tests of git
 198     output.</li>
 199
 200   <li>cvs2git makes no attempt to convert <tt>.cvsignore</tt> files
 201     into <tt>.gitignore</tt> files.</li>
 202
 203   <li>cvs2git, like cvs2svn, does not support incremental conversion
 204     (i.e., tracking a live CVS repository).  However, at least one
 205     person has documented a <a
 206     href="http://www.oak.homeunix.org/~marcel/blog/2009/06/03/tracking-cvs-with-git-using-cvs2git">possible
 207     workaround</a>.</li>
 208
 209 </ul>
 210
 211
 212 <h2><a name="docs">Documentation</a></h2>
 213
 214 <p>There is some documentation specific to cvs2git, and much of the
 215 cvs2svn documentation also applies fairly straightforwardly to
 216 cvs2git.  See the following sources:</p>
 217
 218 <ul>
 219
 220   <li>This document.</li>
 221
 222   <li>The output of <tt>cvs2git --help</tt>.</li>
 223
 224   <li>The cvs2git man page.  If the man page is not installed on your
 225     Unix-like system, you can view it by typing a command like
 226     <tt>cvs2git --man | groff -man -Tascii | less</tt>.</li>
 227
 228   <li><a href="cvs2svn.html#intro">The cvs2svn documentation</a> and
 229     <a href="faq.html">the cvs2svn FAQ</a>, which contain much general
 230     discussion and describe many features that can also be used for
 231     cvs2git.</li>
 232
 233   <li><tt>cvs2git-example.options</tt> in the cvs2svn source tree,
 234     which is an example of an options file that can be used to
 235     configure a cvs2git conversion.  The file is extensively
 236     documented.</li>
 237
 238   <li>The cvs2svn mailing lists, IRC channel, etc., as described in <a
 239     href="faq.html#gettinghelp">the cvs2svn FAQ</a>.</li>
 240
 241 </ul>
 242
 243
 244 <h2><a name="usage">Usage</a></h2>
 245
 246 <p>This section outlines the steps needed to convert a CVS repository
 247 to git using cvs2git.</p>
 248
 249 <ol>
 250
 251   <li>Be sure that you have the <a href="#reqs">requirements</a>,
 252     including either RCS or CVS (used to read revision contents from
 253     the CVS repository).</li>
 254
 255   <li>Obtain a copy of cvs2svn/cvs2git version 2.1 or newer.  It is
 256     recommended that you use the most recent version available, or
 257     even the development version.
 258
 259     <ul>
 260
 261       <li>To install cvs2svn from a <a
 262         href="http://cvs2svn.tigris.org/servlets/ProjectDocumentList">tarball</a>,
 263         simply unpack the tarball into a directory on your conversion
 264         computer (cvs2git can be run directly from this
 265         directory).</li>
 266
 267       <li>
 268
 269         <p>To check out the current trunk version of cvs2svn, make
 270           sure that you have Subversion installed and then run:</p>
 271
 272 <pre>
 273 svn co --username=guest --password="" http://cvs2svn.tigris.org/svn/cvs2svn/trunk cvs2svn-trunk
 274 cd cvs2svn-trunk
 275 make man # If you want to create manpages for the main programs
 276 make check # ...optional
 277 </pre>
 278
 279         <p>Please note that the test suite includes tests that are
 280           marked "XFAIL" (expected failure); these are known and are
 281           not considered serious problems.</p>
 282
 283       </li>
 284
 285     </ul>
 286
 287   </li>
 288
 289   <li>
 290
 291     Configure cvs2git and run the conversion.  This can be done via
 292     command-line options or via an options file:
 293
 294     <ul>
 295
 296       <li>
 297
 298         <p>The command-line options for running cvs2git are documented
 299         in the cvs2git man page and in the output of <tt>cvs2git
 300         --help</tt>.  For example:</p>
 301
 302 <pre>
 303 cvs2git \
 304     --blobfile=cvs2svn-tmp/git-blob.dat \
 305     --dumpfile=cvs2svn-tmp/git-dump.dat \
 306     --username=cvs2git \
 307     /path/to/cvs/repo
 308 </pre>
 309
 310       </li>
 311
 312       <li>
 313
 314         <p>The more flexible <a
 315           href="cvs2svn.html#cmd-vs-options">options-file method</a>
 316           requires you to create an options file, then start cvs2git
 317           with</p>
 318
 319 <pre>
 320 cvs2git --options=OPTIONS-FILE
 321 </pre>
 322
 323         <p>Use <tt>cvs2git-example.options</tt> in the cvs2svn source
 324           tree as your starting point; the file contains lots of
 325           documentation.</p>
 326
 327       </li>
 328
 329     </ul>
 330
 331     <p>This creates two output files in <a
 332     href="http://www.kernel.org/pub/software/scm/git/docs/git-fast-import.html">git
 333     fast-import</a> format.  The names of these files are specified by
 334     your options file or command-line arguments.  In the example,
 335     these files are named <tt>cvs2svn-tmp/git-blob.dat</tt> and
 336     <tt>cvs2svn-tmp/git-dump.dat</tt>.</p>
 337
 338   </li>
 339
 340   <li>
 341
 342     <p>Initialize a git repository:</p>
 343
 344 <pre>
 345 mkdir myproject.git
 346 cd myproject.git
 347 git init --bare
 348 </pre>
 349
 350   </li>
 351
 352   <li>
 353
 354     <p>Load the dump files into the new git repository using <tt>git
 355       fast-import</tt>:</p>
 356
 357 <pre>
 358 git fast-import --export-marks=../cvs2svn-tmp/git-marks.dat &lt; ../cvs2svn-tmp/git-blob.dat
 359 git fast-import --import-marks=../cvs2svn-tmp/git-marks.dat &lt; ../cvs2svn-tmp/git-dump.dat
 360 </pre>
 361
 362     <p>On Linux/Unix this can be shortened to:</p>
 363
 364 <pre>
 365 cat ../cvs2svn-tmp/git-blob.dat ../cvs2svn-tmp/git-dump.dat | git fast-import
 366 </pre>
 367
 368   </li>
 369
 370   <li>
 371
 372     <p>(Optional) View the results of the conversion, for example:</p>
 373
 374 <pre>
 375 gitk --all
 376 </pre>
 377
 378   </li>
 379
 380   <li>(Recommended) To get rid of unnecessary tag fixup branches, run
 381     the <tt>contrib/git-move-refs.py</tt> script from within the git
 382     repository.</li>
 383
 384   <li>
 385
 386     <p>The result of this procedure is a <em>bare</em> git repository
 387       (one that does not have a checked-out version of the source
 388       tree).  This is the type of repository that you would put on
 389       your server.  To work on your project, make a non-bare clone
 390       (one that includes a checked-out source tree):</p>
 391
 392 <pre>
 393 cd $HOME
 394 git clone /path/to/myproject.git
 395 cd myproject
 396 </pre>
 397
 398     <p>Now you are ready to start editing files and committing to
 399       git!</p>
 400
 401   </li>
 402
 403 </ol>
 404
 405 <p>Feedback would be much appreciated, including reports of success
 406   using cvs2git.  Please send comments, bug reports, and patches to
 407   the <a
 408   href="http://cvs2svn.tigris.org/servlets/ProjectMailingListList">cvs2svn
 409   mailing lists</a>.</p>
 410
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