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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>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>
 201
 202   <li>The cvs2svn test suite does not include meaningful tests of git
 203     output.</li>
 204
 205   <li>cvs2git makes no attempt to convert <tt>.cvsignore</tt> files
 206     into <tt>.gitignore</tt> files.</li>
 207
 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="http://www.oak.homeunix.org/~marcel/blog/2009/06/03/tracking-cvs-with-git-using-cvs2git">possible
 212     workaround</a>.</li>
 213
 214 </ul>
 215
 216
 217 <h2><a name="docs">Documentation</a></h2>
 218
 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>
 222
 223 <ul>
 224
 225   <li>This document.</li>
 226
 227   <li>The output of <tt>cvs2git --help</tt>.</li>
 228
 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>
 232
 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>
 237
 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>
 242
 243   <li>The cvs2svn mailing lists, IRC channel, etc., as described in <a
 244     href="faq.html#gettinghelp">the cvs2svn FAQ</a>.</li>
 245
 246 </ul>
 247
 248
 249 <h2><a name="usage">Usage</a></h2>
 250
 251 <p>This section outlines the steps needed to convert a CVS repository
 252 to git using cvs2git.</p>
 253
 254 <ol>
 255
 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>
 259
 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.
 263
 264     <ul>
 265
 266       <li>To install cvs2svn from a <a
 267         href="http://cvs2svn.tigris.org/servlets/ProjectDocumentList">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>
 271
 272       <li>
 273
 274         <p>To check out the current trunk version of cvs2svn, make
 275           sure that you have Subversion installed and then run:</p>
 276
 277 <pre>
 278 svn co --username=guest --password="" http://cvs2svn.tigris.org/svn/cvs2svn/trunk 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>
 283
 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>
 287
 288       </li>
 289
 290     </ul>
 291
 292   </li>
 293
 294   <li>
 295
 296     Configure cvs2git for your conversion.  This can be done via
 297     command-line options or via an options file:
 298
 299     <ul>
 300
 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>
 304
 305       <li>
 306
 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>
 311
 312 <pre>
 313 cvs2git --options=OPTIONS-FILE
 314 </pre>
 315
 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>
 319
 320       </li>
 321
 322     </ul>
 323
 324   </li>
 325
 326   <li>
 327
 328     <p>Run cvs2git.  This creates two output files in <a
 329     href="http://www.kernel.org/pub/software/scm/git/docs/git-fast-import.html">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>
 334
 335   </li>
 336
 337   <li>
 338
 339     <p>Initialize a git repository, and load the dump files using
 340       git fast-import:</p>
 341
 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>
 347
 348     <p>This can, of course, be shortened to:</p>
 349
 350 <pre>
 351 git init
 352 cat cvs2svn-tmp/git-blob.dat cvs2svn-tmp/git-dump.dat | git fast-import
 353 </pre>
 354
 355   </li>
 356
 357   <li>If you want to get rid of unnecessary tag fixup branches, then
 358     run the <tt>contrib/git-move-refs.py</tt> script from within the
 359     git repository.</li>
 360
 361 </ol>
 362
 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="http://cvs2svn.tigris.org/servlets/ProjectMailingListList">cvs2svn
 367   mailing lists</a>.</p>
 368
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