git for CVS users
=================
-So you're a CVS user. That's OK, it's a treatable condition. The job of
-this document is to put you on the road to recovery, by helping you
-convert an existing cvs repository to git, and by showing you how to use a
-git repository in a cvs-like fashion.
+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.
-First, note some ways that git differs from CVS:
+Developing against a shared repository
+--------------------------------------
- * Commits are atomic and project-wide, not per-file as in CVS.
-
- * Offline work is supported: you can make multiple commits locally,
- then submit them when you're ready.
-
- * Branching is fast and easy.
+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:
- * 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; see below
- for details.
+------------------------------------------------
+$ git clone foo.com:/pub/repo.git/ my-project
+$ cd my-project
+------------------------------------------------
-Importing a CVS archive
------------------------
+and hack away. The equivalent of `cvs update` is
-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. The magic command line is then
+------------------------------------------------
+$ git pull origin
+------------------------------------------------
--------------------------------------------
-$ git cvsimport -v -d <cvsroot> -C <destination> <module>
--------------------------------------------
+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.
-This puts a git archive of the named CVS module in the directory
-<destination>, which will be created if necessary. The -v option makes
-the conversion script very chatty.
+[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 config -l` and the gitlink:git-config[1] man
+page for details.
+================================
-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.
+You can update the shared repository with your changes by first committing
+your changes, and then using the gitlink:git-push[1] command:
-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.
+------------------------------------------------
+$ git push origin master
+------------------------------------------------
-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.
+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.
-Development Models
-------------------
+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:
-CVS users are accustomed to giving a group of developers commit access to
-a common repository. In the next section we'll explain how to do this
-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.
+------------
+$ git push origin
+$ git push foo.com:/pub/project.git/
+------------
-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.
+as long as the shared repository does not have any branches
+other than `master`.
-With a small group, developers may just pull changes from each other's
-repositories without the need for a central maintainer.
+Setting Up a Shared Repository
+------------------------------
-Emulating the CVS Development Model
------------------------------------
+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).
-Start with an ordinary git working directory containing the project, and
-remove the checked-out files, keeping just the bare .git directory:
+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:
------------------------------------------------
-$ mv project/.git /pub/repo.git
-$ rm -r project/
+$ mkdir /pub/my-repo.git
+$ cd /pub/my-repo.git
+$ git --bare init --shared
+$ git --bare fetch /home/alice/myproject master:master
------------------------------------------------
Next, give every team member read/write access to this repository. One
writable by that group:
------------------------------------------------
-$ chgrp -R $group repo.git
-$ find repo.git -mindepth 1 -type d |xargs chmod ug+rwx,g+s
-$ GIT_DIR=repo.git git repo-config core.sharedrepository true
+$ chgrp -R $group /pub/my-repo.git
------------------------------------------------
Make sure committers have a umask of at most 027, so that the directories
they create are writable and searchable by other group members.
-Suppose this repository is now set up in /pub/repo.git on the host
-foo.com. Then as an individual committer you can clone the shared
-repository:
-
-------------------------------------------------
-$ git clone foo.com:/pub/repo.git/ my-project
-$ cd my-project
-------------------------------------------------
-
-and hack away. The equivalent of `cvs update` is
-
-------------------------------------------------
-$ git pull origin
-------------------------------------------------
-
-which merges in any work that others might have done since the clone
-operation.
-
-[NOTE]
-================================
-The first `git clone` places the following in the
-`my-project/.git/remotes/origin` file, and that's why the previous step
-and the next step both work.
-------------
-URL: foo.com:/pub/project.git/ my-project
-Pull: master:origin
-------------
-================================
-
-You can update the shared repository with your changes using:
+Importing a CVS archive
+-----------------------
-------------------------------------------------
-$ git push origin master
-------------------------------------------------
+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]:
-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.
+-------------------------------------------
+$ git cvsimport -C <destination>
+-------------------------------------------
-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:
+This puts a git archive of the named CVS module in the directory
+<destination>, which will be created if necessary.
-------------
-$ git push origin
-$ git push repo.shared.xz:/pub/scm/project.git/
-------------
+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.
-as long as the shared repository does not have any branches
-other than `master`.
+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.
-[NOTE]
-============
-Because of this behavior, if the shared repository and the developer's
-repository both have branches named `origin`, then a push like the above
-attempts to update the `origin` branch in the shared repository from the
-developer's `origin` branch. The results may be unexpected, so it's
-usually best to remove any branch named `origin` from the shared
-repository.
-============
+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
-------------------------------------
link:howto/update-hook-example.txt[Controlling access to branches using
update hooks].
-CVS annotate
-------------
+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.
-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 archaeologist").
-
-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
-of 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 (otherwise you should go back and read the tutorial).
-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 a 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".
-
-NOTE: The current version 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
-
-NOTE: This option is called "--pickaxe-all" because -S
- option is internally called "pickaxe", a tool for software
- archaeologists.
+With a small group, developers may just pull changes from each other's
+repositories without the need for a central maintainer.