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-Git for CVS users
+git for CVS users
=================
-Ok, so you're a CVS user. That's ok, it's a treatable condition, and the
-first step to recovery is admitting you have a problem. The fact that
-you are reading this file means that you may be well on that path
-already.
-
-The thing about CVS is that it absolutely sucks as a source control
-manager, and you'll thus be happy with almost anything else. Git,
-however, may be a bit _too_ different (read: "good") for your taste, and
-does a lot of things differently.
-
-One particular suckage of CVS is very hard to work around: CVS is
-basically a tool for tracking _file_ history, while git is a tool for
-tracking _project_ history. This sometimes causes problems if you are
-used to doing very strange things in CVS, in particular if you're doing
-things like making branches of just a subset of the project. Git can't
-track that, since git never tracks things on the level of an individual
-file, only on the whole project level.
-
-The good news is that most people don't do that, and in fact most sane
-people think it's a bug in CVS that makes it tag (and check in changes)
-one file at a time. So most projects you'll ever see will use CVS
-_as_if_ it was sane. In which case you'll find it very easy indeed to
-move over to Git.
-
-First off: this is not a git tutorial. See Documentation/tutorial.txt
-for how git actually works. This is more of a random collection of
-gotcha's and notes on converting from CVS to git.
-
-Second: CVS has the notion of a "repository" as opposed to the thing
-that you're actually working in (your working directory, or your
-"checked out tree"). Git does not have that notion at all, and all git
-working directories _are_ the repositories. However, you can easily
-emulate the CVS model by having one special "global repository", which
-people can synchronize with. See details later, but in the meantime
-just keep in mind that with git, every checked out working tree will
-have a full revision control history of its own.
+Git differs from CVS in that every working tree contains a repository with
+a full copy of the project history, and no repository is inherently more
+important than any other. However, you can emulate the CVS model by
+designating a single shared repository which people can synchronize with;
+this document explains how to do that.
+Some basic familiarity with git is required. This
+link:tutorial.html[tutorial introduction to git] should be sufficient.
-Importing a CVS archive
------------------------
+Developing against a shared repository
+--------------------------------------
-Ok, you have an old project, and you want to at least give git a chance
-to see how it performs. The first thing you want to do (after you've
-gone through the git tutorial, and generally familiarized yourself with
-how to commit stuff etc in git) is to create a git'ified version of your
-CVS archive.
+Suppose a shared repository is set up in /pub/repo.git on the host
+foo.com. Then as an individual committer you can clone the shared
+repository over ssh with:
-Happily, that's very easy indeed. Git will do it for you, although git
-will need the help of a program called "cvsps":
+------------------------------------------------
+$ git clone foo.com:/pub/repo.git/ my-project
+$ cd my-project
+------------------------------------------------
- http://www.cobite.com/cvsps/
+and hack away. The equivalent of `cvs update` is
-which is not actually related to git at all, but which makes CVS usage
-look almost sane (ie you almost certainly want to have it even if you
-decide to stay with CVS). However, git will want at _least_ version 2.1
-of cvsps (available at the address above), and in fact will currently
-refuse to work with anything else.
+------------------------------------------------
+$ git pull origin
+------------------------------------------------
-Once you've gotten (and installed) cvsps, you may or may not want to get
-any more familiar with it, but make sure it is in your path. After that,
-the magic command line is
+which merges in any work that others might have done since the clone
+operation. If there are uncommitted changes in your working tree, commit
+them first before running git pull.
- git cvsimport <cvsroot> <module>
+[NOTE]
+================================
+The `pull` command knows where to get updates from because of certain
+configuration variables that were set by the first `git clone`
+command; see `git repo-config -l` and the gitlink:git-repo-config[1] man
+page for details.
+================================
-which will do exactly what you'd think it does: it will create a git
-archive of the named CVS module. The new archive will be created in a
-subdirectory named <module>.
+You can update the shared repository with your changes by first committing
+your changes, and then using the gitlink:git-push[1] command:
-It can take some time to actually do the conversion for a large archive
-since it involves checking out from CVS every revision of every file,
-and the conversion script can be reasonably chatty, but on some not very
-scientific tests it averaged about eight revisions per second, so a
-medium-sized project should not take more than a couple of minutes. For
-larger projects or remote repositories, the process may take longer.
+------------------------------------------------
+$ git push origin master
+------------------------------------------------
+to "push" those commits to the shared repository. If someone else has
+updated the repository more recently, `git push`, like `cvs commit`, will
+complain, in which case you must pull any changes before attempting the
+push again.
-Emulating CVS behaviour
------------------------
+In the `git push` command above we specify the name of the remote branch
+to update (`master`). If we leave that out, `git push` tries to update
+any branches in the remote repository that have the same name as a branch
+in the local repository. So the last `push` can be done with either of:
+------------
+$ git push origin
+$ git push foo.com:/pub/project.git/
+------------
-FIXME! Talk about setting up several repositories, and pulling and
-pushing between them. Talk about merging, and branches. Some of this
-needs to be in the tutorial too.
+as long as the shared repository does not have any branches
+other than `master`.
+Setting Up a Shared Repository
+------------------------------
+We assume you have already created a git repository for your project,
+possibly created from scratch or from a tarball (see the
+link:tutorial.html[tutorial]), or imported from an already existing CVS
+repository (see the next section).
-CVS annotate
-------------
+Assume your existing repo is at /home/alice/myproject. Create a new "bare"
+repository (a repository without a working tree) and fetch your project into
+it:
+
+------------------------------------------------
+$ mkdir /pub/my-repo.git
+$ cd /pub/my-repo.git
+$ git --bare init-db --shared
+$ git --bare fetch /home/alice/myproject master:master
+------------------------------------------------
+
+Next, give every team member read/write access to this repository. One
+easy way to do this is to give all the team members ssh access to the
+machine where the repository is hosted. If you don't want to give them a
+full shell on the machine, there is a restricted shell which only allows
+users to do git pushes and pulls; see gitlink:git-shell[1].
+
+Put all the committers in the same group, and make the repository
+writable by that group:
+
+------------------------------------------------
+$ chgrp -R $group /pub/my-repo.git
+------------------------------------------------
+
+Make sure committers have a umask of at most 027, so that the directories
+they create are writable and searchable by other group members.
+
+Importing a CVS archive
+-----------------------
-So, something has gone wrong, and you don't know whom to blame, and
-you're an ex-CVS user and used to do "cvs annotate" to see who caused
-the breakage. You're looking for the "git annotate", and it's just
-claiming not to find such a script. You're annoyed.
-
-Yes, that's right. Core git doesn't do "annotate", although it's
-technically possible, and there are at least two specialized scripts out
-there that can be used to get equivalent information (see the git
-mailing list archives for details).
-
-Git has a couple of alternatives, though, that you may find sufficient
-or even superior depending on your use. One is called "git-whatchanged"
-(for obvious reasons) and the other one is called "pickaxe" ("a tool for
-the software archeologist").
-
-The "git-whatchanged" script is a truly trivial script that can give you
-a good overview of what has changed in a file or a directory (or an
-arbitrary list of files or directories). The "pickaxe" support is an
-additional layer that can be used to further specify exactly what you're
-looking for, if you already know the specific area that changed.
-
-Let's step back a bit and think about the reason why you would
-want to do "cvs annotate a-file.c" to begin with.
-
-You would use "cvs annotate" on a file when you have trouble
-with a function (or even a single "if" statement in a function)
-that happens to be defined in the file, which does not do what
-you want it to do. And you would want to find out why it was
-written that way, because you are about to modify it to suit
-your needs, and at the same time you do not want to break its
-current callers. For that, you are trying to find out why the
-original author did things that way in the original context.
-
-Many times, it may be enough to see the commit log messages of
-commits that touch the file in question, possibly along with the
-patches themselves, like this:
-
- $ git-whatchanged -p a-file.c
-
-This will show log messages and patches for each commit that
-touches a-file.
-
-This, however, may not be very useful when this file has many
-modifications that are not related to the piece of code you are
-interested in. You would see many log messages and patches that
-do not have anything to do with the piece of code you are
-interested in. As an example, assuming that you have this piece
-code that you are interested in in the HEAD version:
-
- if (frotz) {
- nitfol();
- }
-
-you would use git-rev-list and git-diff-tree like this:
-
- $ git-rev-list HEAD |
- git-diff-tree --stdin -v -p -S'if (frotz) {
- nitfol();
- }'
-
-We have already talked about the "--stdin" form of git-diff-tree
-command that reads the list of commits and compares each commit
-with its parents. The git-whatchanged command internally runs
-the equivalent of the above command, and can be used like this:
-
- $ git-whatchanged -p -S'if (frotz) {
- nitfol();
- }'
-
-When the -S option is used, git-diff-tree command outputs
-differences between two commits only if one tree has the
-specified string in a file and the corresponding file in the
-other tree does not. The above example looks for a commit that
-has the "if" statement in it in a file, but its parent commit
-does not have it in the same shape in the corresponding file (or
-the other way around, where the parent has it and the commit
-does not), and the differences between them are shown, along
-with the commit message (thanks to the -v flag). It does not
-show anything for commits that do not touch this "if" statement.
-
-Also, in the original context, the same statement might have
-appeared at first in a different file and later the file was
-renamed to "a-file.c". CVS annotate would not help you to go
-back across such a rename, but GIT would still help you in such
-a situation. For that, you can give the -C flag to
-git-diff-tree, like this:
-
- $ git-whatchanged -p -C -S'if (frotz) {
- nitfol();
- }'
-
-When the -C flag is used, file renames and copies are followed.
-So if the "if" statement in question happens to be in "a-file.c"
-in the current HEAD commit, even if the file was originally
-called "o-file.c" and then renamed in an earlier commit, or if
-the file was created by copying an existing "o-file.c" in an
-earlier commit, you will not lose track. If the "if" statement
-did not change across such rename or copy, then the commit that
-does rename or copy would not show in the output, and if the
-"if" statement was modified while the file was still called
-"o-file.c", it would find the commit that changed the statement
-when it was in "o-file.c".
-
-[ BTW, the current versions of "git-diff-tree -C" is not eager
- enough to find copies, and it will miss the fact that a-file.c
- was created by copying o-file.c unless o-file.c was somehow
- changed in the same commit.]
-
-You can use the --pickaxe-all flag in addition to the -S flag.
-This causes the differences from all the files contained in
-those two commits, not just the differences between the files
-that contain this changed "if" statement:
-
- $ git-whatchanged -p -C -S'if (frotz) {
- nitfol();
- }' --pickaxe-all
-
-[ Side note. This option is called "--pickaxe-all" because -S
- option is internally called "pickaxe", a tool for software
- archaeologists.]
+First, install version 2.1 or higher of cvsps from
+link:http://www.cobite.com/cvsps/[http://www.cobite.com/cvsps/] and make
+sure it is in your path. Then cd to a checked out CVS working directory
+of the project you are interested in and run gitlink:git-cvsimport[1]:
+
+-------------------------------------------
+$ git cvsimport -C <destination>
+-------------------------------------------
+
+This puts a git archive of the named CVS module in the directory
+<destination>, which will be created if necessary.
+
+The import checks out from CVS every revision of every file. Reportedly
+cvsimport can average some twenty revisions per second, so for a
+medium-sized project this should not take more than a couple of minutes.
+Larger projects or remote repositories may take longer.
+
+The main trunk is stored in the git branch named `origin`, and additional
+CVS branches are stored in git branches with the same names. The most
+recent version of the main trunk is also left checked out on the `master`
+branch, so you can start adding your own changes right away.
+
+The import is incremental, so if you call it again next month it will
+fetch any CVS updates that have been made in the meantime. For this to
+work, you must not modify the imported branches; instead, create new
+branches for your own changes, and merge in the imported branches as
+necessary.
+
+Advanced Shared Repository Management
+-------------------------------------
+
+Git allows you to specify scripts called "hooks" to be run at certain
+points. You can use these, for example, to send all commits to the shared
+repository to a mailing list. See link:hooks.html[Hooks used by git].
+
+You can enforce finer grained permissions using update hooks. See
+link:howto/update-hook-example.txt[Controlling access to branches using
+update hooks].
+
+Providing CVS Access to a git Repository
+----------------------------------------
+
+It is also possible to provide true CVS access to a git repository, so
+that developers can still use CVS; see gitlink:git-cvsserver[1] for
+details.
+
+Alternative Development Models
+------------------------------
+
+CVS users are accustomed to giving a group of developers commit access to
+a common repository. As we've seen, this is also possible with git.
+However, the distributed nature of git allows other development models,
+and you may want to first consider whether one of them might be a better
+fit for your project.
+
+For example, you can choose a single person to maintain the project's
+primary public repository. Other developers then clone this repository
+and each work in their own clone. When they have a series of changes that
+they're happy with, they ask the maintainer to pull from the branch
+containing the changes. The maintainer reviews their changes and pulls
+them into the primary repository, which other developers pull from as
+necessary to stay coordinated. The Linux kernel and other projects use
+variants of this model.
+
+With a small group, developers may just pull changes from each other's
+repositories without the need for a central maintainer.