| <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Git User's Manual</title><meta name="generator" content="DocBook XSL Stylesheets V1.69.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" lang="en"><div class="titlepage"><div><div><h1 class="title"><a name="id189263"></a>Git User's Manual</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="preface"><a href="#id264751">Preface</a></span></dt><dt><span class="chapter"><a href="#id233181">1. Git Quick Start</a></span></dt><dd><dl><dt><span class="section"><a href="#id233192">Creating a new repository</a></span></dt><dt><span class="section"><a href="#id233223">Managing branches</a></span></dt><dt><span class="section"><a href="#id233456">Exploring history</a></span></dt><dt><span class="section"><a href="#id233500">Making changes</a></span></dt><dt><span class="section"><a href="#id232938">Merging</a></span></dt><dt><span class="section"><a href="#id232955">Sharing your changes</a></span></dt><dt><span class="section"><a href="#id233039">Repository maintenance</a></span></dt></dl></dd><dt><span class="chapter"><a href="#id232541">2. Repositories and Branches</a></span></dt><dd><dl><dt><span class="section"><a href="#id232547">How to get a git repository</a></span></dt><dt><span class="section"><a href="#id232603">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#id273448">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#id273497">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#id273537">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#id273565">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#id232302">Manipulating branches</a></span></dt><dt><span class="section"><a href="#id273789">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-with-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#id274034">Fetching branches from other repositories</a></span></dt></dl></dd><dt><span class="chapter"><a href="#id274109">3. Exploring git history</a></span></dt><dd><dl><dt><span class="section"><a href="#id274131">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#id274250">Naming commits</a></span></dt><dt><span class="section"><a href="#id274501">Creating tags</a></span></dt><dt><span class="section"><a href="#id274536">Browsing revisions</a></span></dt><dt><span class="section"><a href="#id274610">Generating diffs</a></span></dt><dt><span class="section"><a href="#id274653">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#id274679">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#id274685">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#id274738">Find first tagged version including a given fix</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#id274901">4. Developing with git</a></span></dt><dd><dl><dt><span class="section"><a href="#id274907">Telling git your name</a></span></dt><dt><span class="section"><a href="#id274939">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">how to make a commit</a></span></dt><dt><span class="section"><a href="#id275166">creating good commit messages</a></span></dt><dt><span class="section"><a href="#id275182">how to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dt><span class="section"><a href="#undoing-a-merge">undoing a merge</a></span></dt><dt><span class="section"><a href="#id275418">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#id275447">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#id275500">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#id275558">Fixing a mistake by editing history</a></span></dt><dt><span class="section"><a href="#id275628">Checking out an old version of a file</a></span></dt></dl></dd><dt><span class="section"><a href="#id275687">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#id275724">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#id275730">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#id275805">Recovering lost changes</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#id275955">5. Sharing development with others</a></span></dt><dd><dl><dt><span class="section"><a href="#getting-updates-with-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#id276086">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#id276136">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via http</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a git repository via the git protocol</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#id276548">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#id276567">Allow web browsing of a repository</a></span></dt><dt><span class="section"><a href="#id276579">Examples</a></span></dt></dl></dd><dt><span class="chapter"><a href="#cleaning-up-history">6. Rewriting history and maintaining patch series</a></span></dt><dd><dl><dt><span class="section"><a href="#id276611">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#id276686">Keeping a patch series up to date using git-rebase</a></span></dt><dt><span class="section"><a href="#id276817">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#id276878">Other tools</a></span></dt><dt><span class="section"><a href="#id276891">Problems with rewriting history</a></span></dt></dl></dd><dt><span class="chapter"><a href="#id276962">7. Advanced branch management</a></span></dt><dd><dl><dt><span class="section"><a href="#id276968">Fetching individual branches</a></span></dt><dt><span class="section"><a href="#fast-forwards">Understanding git history: fast-forwards</a></span></dt><dt><span class="section"><a href="#id277088">Forcing git fetch to do non-fast-forward updates</a></span></dt><dt><span class="section"><a href="#id277115">Configuring remote branches</a></span></dt></dl></dd><dt><span class="chapter"><a href="#id277239">8. Git internals</a></span></dt><dd><dl><dt><span class="section"><a href="#id277250">The Object Database</a></span></dt><dt><span class="section"><a href="#id277365">Blob Object</a></span></dt><dt><span class="section"><a href="#id277409">Tree Object</a></span></dt><dt><span class="section"><a href="#id277486">Commit Object</a></span></dt><dt><span class="section"><a href="#id277533">Trust</a></span></dt><dt><span class="section"><a href="#id277583">Tag Object</a></span></dt><dt><span class="section"><a href="#id277630">The "index" aka "Current Directory Cache"</a></span></dt><dt><span class="section"><a href="#id277705">The Workflow</a></span></dt><dd><dl><dt><span class="section"><a href="#id277724">working directory -> index</a></span></dt><dt><span class="section"><a href="#id277813">index -> object database</a></span></dt><dt><span class="section"><a href="#id277841">object database -> index</a></span></dt><dt><span class="section"><a href="#id277872">index -> working directory</a></span></dt><dt><span class="section"><a href="#id277936">Tying it all together</a></span></dt></dl></dd><dt><span class="section"><a href="#id278030">Examining the data</a></span></dt><dt><span class="section"><a href="#id278108">Merging multiple trees</a></span></dt><dt><span class="section"><a href="#id278195">Merging multiple trees, continued</a></span></dt><dt><span class="section"><a href="#id278455">How git stores objects efficiently: pack files</a></span></dt><dt><span class="section"><a href="#dangling-objects">Dangling objects</a></span></dt></dl></dd><dt><span class="chapter"><a href="#id278715">9. Glossary of git terms</a></span></dt><dt><span class="chapter"><a href="#id279930">10. Notes and todo list for this manual</a></span></dt></dl></div><div class="preface" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id264751"></a>Preface</h2></div></div></div><p>This manual is designed to be readable by someone with basic unix |
| command-line skills, but no previous knowledge of git.</p><p>Chapter 1 gives a brief overview of git commands, without any |
| explanation; you may prefer to skip to chapter 2 on a first reading.</p><p>Chapters 2 and 3 explain how to fetch and study a project using |
| git—the tools you'd need to build and test a particular version of a |
| software project, to search for regressions, and so on.</p><p>Chapter 4 explains how to do development with git, and chapter 5 how |
| to share that development with others.</p><p>Further chapters cover more specialized topics.</p><p>Comprehensive reference documentation is available through the man |
| pages. For a command such as "git clone", just use</p><div class="literallayout"><p>$ man git-clone</p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id233181"></a>Chapter 1. Git Quick Start</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id233192">Creating a new repository</a></span></dt><dt><span class="section"><a href="#id233223">Managing branches</a></span></dt><dt><span class="section"><a href="#id233456">Exploring history</a></span></dt><dt><span class="section"><a href="#id233500">Making changes</a></span></dt><dt><span class="section"><a href="#id232938">Merging</a></span></dt><dt><span class="section"><a href="#id232955">Sharing your changes</a></span></dt><dt><span class="section"><a href="#id233039">Repository maintenance</a></span></dt></dl></div><p>This is a quick summary of the major commands; the following chapters |
| will explain how these work in more detail.</p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id233192"></a>Creating a new repository</h2></div></div></div><p>From a tarball:</p><div class="literallayout"><p>$ tar xzf project.tar.gz<br> |
| $ cd project<br> |
| $ git init<br> |
| Initialized empty Git repository in .git/<br> |
| $ git add .<br> |
| $ git commit</p></div><p>From a remote repository:</p><div class="literallayout"><p>$ git clone git://example.com/pub/project.git<br> |
| $ cd project</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id233223"></a>Managing branches</h2></div></div></div><div class="literallayout"><p>$ git branch # list all branches in this repo<br> |
| $ git checkout test # switch working directory to branch "test"<br> |
| $ git branch new # create branch "new" starting at current HEAD<br> |
| $ git branch -d new # delete branch "new"</p></div><p>Instead of basing new branch on current HEAD (the default), use:</p><div class="literallayout"><p>$ git branch new test # branch named "test"<br> |
| $ git branch new v2.6.15 # tag named v2.6.15<br> |
| $ git branch new HEAD^ # commit before the most recent<br> |
| $ git branch new HEAD^^ # commit before that<br> |
| $ git branch new test~10 # ten commits before tip of branch "test"</p></div><p>Create and switch to a new branch at the same time:</p><div class="literallayout"><p>$ git checkout -b new v2.6.15</p></div><p>Update and examine branches from the repository you cloned from:</p><div class="literallayout"><p>$ git fetch # update<br> |
| $ git branch -r # list<br> |
| origin/master<br> |
| origin/next<br> |
| ...<br> |
| $ git branch checkout -b masterwork origin/master</p></div><p>Fetch a branch from a different repository, and give it a new |
| name in your repository:</p><div class="literallayout"><p>$ git fetch git://example.com/project.git theirbranch:mybranch<br> |
| $ git fetch git://example.com/project.git v2.6.15:mybranch</p></div><p>Keep a list of repositories you work with regularly:</p><div class="literallayout"><p>$ git remote add example git://example.com/project.git<br> |
| $ git remote # list remote repositories<br> |
| example<br> |
| origin<br> |
| $ git remote show example # get details<br> |
| * remote example<br> |
| URL: git://example.com/project.git<br> |
| Tracked remote branches<br> |
| master next ...<br> |
| $ git fetch example # update branches from example<br> |
| $ git branch -r # list all remote branches</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id233456"></a>Exploring history</h2></div></div></div><div class="literallayout"><p>$ gitk # visualize and browse history<br> |
| $ git log # list all commits<br> |
| $ git log src/ # ...modifying src/<br> |
| $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15<br> |
| $ git log master..test # ...in branch test, not in branch master<br> |
| $ git log test..master # ...in branch master, but not in test<br> |
| $ git log test...master # ...in one branch, not in both<br> |
| $ git log -S'foo()' # ...where difference contain "foo()"<br> |
| $ git log --since="2 weeks ago"<br> |
| $ git log -p # show patches as well<br> |
| $ git show # most recent commit<br> |
| $ git diff v2.6.15..v2.6.16 # diff between two tagged versions<br> |
| $ git diff v2.6.15..HEAD # diff with current head<br> |
| $ git grep "foo()" # search working directory for "foo()"<br> |
| $ git grep v2.6.15 "foo()" # search old tree for "foo()"<br> |
| $ git show v2.6.15:a.txt # look at old version of a.txt</p></div><p>Search for regressions:</p><div class="literallayout"><p>$ git bisect start<br> |
| $ git bisect bad # current version is bad<br> |
| $ git bisect good v2.6.13-rc2 # last known good revision<br> |
| Bisecting: 675 revisions left to test after this<br> |
| # test here, then:<br> |
| $ git bisect good # if this revision is good, or<br> |
| $ git bisect bad # if this revision is bad.<br> |
| # repeat until done.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id233500"></a>Making changes</h2></div></div></div><p>Make sure git knows who to blame:</p><div class="literallayout"><p>$ cat >~/.gitconfig <<\EOF<br> |
| [user]<br> |
| name = Your Name Comes Here<br> |
| email = you@yourdomain.example.com<br> |
| EOF</p></div><p>Select file contents to include in the next commit, then make the |
| commit:</p><div class="literallayout"><p>$ git add a.txt # updated file<br> |
| $ git add b.txt # new file<br> |
| $ git rm c.txt # old file<br> |
| $ git commit</p></div><p>Or, prepare and create the commit in one step:</p><div class="literallayout"><p>$ git commit d.txt # use latest content only of d.txt<br> |
| $ git commit -a # use latest content of all tracked files</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id232938"></a>Merging</h2></div></div></div><div class="literallayout"><p>$ git merge test # merge branch "test" into the current branch<br> |
| $ git pull git://example.com/project.git master<br> |
| # fetch and merge in remote branch<br> |
| $ git pull . test # equivalent to git merge test</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id232955"></a>Sharing your changes</h2></div></div></div><p>Importing or exporting patches:</p><div class="literallayout"><p>$ git format-patch origin..HEAD # format a patch for each commit<br> |
| # in HEAD but not in origin<br> |
| $ git-am mbox # import patches from the mailbox "mbox"</p></div><p>Fetch a branch in a different git repository, then merge into the |
| current branch:</p><div class="literallayout"><p>$ git pull git://example.com/project.git theirbranch</p></div><p>Store the fetched branch into a local branch before merging into the |
| current branch:</p><div class="literallayout"><p>$ git pull git://example.com/project.git theirbranch:mybranch</p></div><p>After creating commits on a local branch, update the remote |
| branch with your commits:</p><div class="literallayout"><p>$ git push ssh://example.com/project.git mybranch:theirbranch</p></div><p>When remote and local branch are both named "test":</p><div class="literallayout"><p>$ git push ssh://example.com/project.git test</p></div><p>Shortcut version for a frequently used remote repository:</p><div class="literallayout"><p>$ git remote add example ssh://example.com/project.git<br> |
| $ git push example test</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id233039"></a>Repository maintenance</h2></div></div></div><p>Check for corruption:</p><div class="literallayout"><p>$ git fsck</p></div><p>Recompress, remove unused cruft:</p><div class="literallayout"><p>$ git gc</p></div></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id232541"></a>Chapter 2. Repositories and Branches</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id232547">How to get a git repository</a></span></dt><dt><span class="section"><a href="#id232603">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#id273448">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#id273497">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#id273537">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#id273565">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#id232302">Manipulating branches</a></span></dt><dt><span class="section"><a href="#id273789">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-with-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#id274034">Fetching branches from other repositories</a></span></dt></dl></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id232547"></a>How to get a git repository</h2></div></div></div><p>It will be useful to have a git repository to experiment with as you |
| read this manual.</p><p>The best way to get one is by using the <a href="git-clone.html" target="_top">git-clone(1)</a> command |
| to download a copy of an existing repository for a project that you |
| are interested in. If you don't already have a project in mind, here |
| are some interesting examples:</p><div class="literallayout"><p> # git itself (approx. 10MB download):<br> |
| $ git clone git://git.kernel.org/pub/scm/git/git.git<br> |
| # the linux kernel (approx. 150MB download):<br> |
| $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git</p></div><p>The initial clone may be time-consuming for a large project, but you |
| will only need to clone once.</p><p>The clone command creates a new directory named after the project |
| ("git" or "linux-2.6" in the examples above). After you cd into this |
| directory, you will see that it contains a copy of the project files, |
| together with a special top-level directory named ".git", which |
| contains all the information about the history of the project.</p><p>In most of the following, examples will be taken from one of the two |
| repositories above.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id232603"></a>How to check out a different version of a project</h2></div></div></div><p>Git is best thought of as a tool for storing the history of a |
| collection of files. It stores the history as a compressed |
| collection of interrelated snapshots (versions) of the project's |
| contents.</p><p>A single git repository may contain multiple branches. Each branch |
| is a bookmark referencing a particular point in the project history. |
| The <a href="git-branch.html" target="_top">git-branch(1)</a> command shows you the list of branches:</p><div class="literallayout"><p>$ git branch<br> |
| * master</p></div><p>A freshly cloned repository contains a single branch, named "master", |
| and the working directory contains the version of the project |
| referred to by the master branch.</p><p>Most projects also use tags. Tags, like branches, are references |
| into the project's history, and can be listed using the |
| <a href="git-tag.html" target="_top">git-tag(1)</a> command:</p><div class="literallayout"><p>$ git tag -l<br> |
| v2.6.11<br> |
| v2.6.11-tree<br> |
| v2.6.12<br> |
| v2.6.12-rc2<br> |
| v2.6.12-rc3<br> |
| v2.6.12-rc4<br> |
| v2.6.12-rc5<br> |
| v2.6.12-rc6<br> |
| v2.6.13<br> |
| ...</p></div><p>Tags are expected to always point at the same version of a project, |
| while branches are expected to advance as development progresses.</p><p>Create a new branch pointing to one of these versions and check it |
| out using <a href="git-checkout.html" target="_top">git-checkout(1)</a>:</p><div class="literallayout"><p>$ git checkout -b new v2.6.13</p></div><p>The working directory then reflects the contents that the project had |
| when it was tagged v2.6.13, and <a href="git-branch.html" target="_top">git-branch(1)</a> shows two |
| branches, with an asterisk marking the currently checked-out branch:</p><div class="literallayout"><p>$ git branch<br> |
| master<br> |
| * new</p></div><p>If you decide that you'd rather see version 2.6.17, you can modify |
| the current branch to point at v2.6.17 instead, with</p><div class="literallayout"><p>$ git reset --hard v2.6.17</p></div><p>Note that if the current branch was your only reference to a |
| particular point in history, then resetting that branch may leave you |
| with no way to find the history it used to point to; so use this |
| command carefully.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id273448"></a>Understanding History: Commits</h2></div></div></div><p>Every change in the history of a project is represented by a commit. |
| The <a href="git-show.html" target="_top">git-show(1)</a> command shows the most recent commit on the |
| current branch:</p><div class="literallayout"><p>$ git show<br> |
| commit 2b5f6dcce5bf94b9b119e9ed8d537098ec61c3d2<br> |
| Author: Jamal Hadi Salim <hadi@cyberus.ca><br> |
| Date: Sat Dec 2 22:22:25 2006 -0800<br> |
| <br> |
| [XFRM]: Fix aevent structuring to be more complete.<br> |
| <br> |
| aevents can not uniquely identify an SA. We break the ABI with this<br> |
| patch, but consensus is that since it is not yet utilized by any<br> |
| (known) application then it is fine (better do it now than later).<br> |
| <br> |
| Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca><br> |
| Signed-off-by: David S. Miller <davem@davemloft.net><br> |
| <br> |
| diff --git a/Documentation/networking/xfrm_sync.txt b/Documentation/networking/xfrm_sync.txt<br> |
| index 8be626f..d7aac9d 100644<br> |
| --- a/Documentation/networking/xfrm_sync.txt<br> |
| +++ b/Documentation/networking/xfrm_sync.txt<br> |
| @@ -47,10 +47,13 @@ aevent_id structure looks like:<br> |
| <br> |
| struct xfrm_aevent_id {<br> |
| struct xfrm_usersa_id sa_id;<br> |
| + xfrm_address_t saddr;<br> |
| __u32 flags;<br> |
| + __u32 reqid;<br> |
| };<br> |
| ...</p></div><p>As you can see, a commit shows who made the latest change, what they |
| did, and why.</p><p>Every commit has a 40-hexdigit id, sometimes called the "object name" |
| or the "SHA1 id", shown on the first line of the "git show" output. |
| You can usually refer to a commit by a shorter name, such as a tag or a |
| branch name, but this longer name can also be useful. Most |
| importantly, it is a globally unique name for this commit: so if you |
| tell somebody else the object name (for example in email), then you are |
| guaranteed that name will refer to the same commit in their repository |
| that it does in yours (assuming their repository has that commit at |
| all).</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id273497"></a>Understanding history: commits, parents, and reachability</h3></div></div></div><p>Every commit (except the very first commit in a project) also has a |
| parent commit which shows what happened before this commit. |
| Following the chain of parents will eventually take you back to the |
| beginning of the project.</p><p>However, the commits do not form a simple list; git allows lines of |
| development to diverge and then reconverge, and the point where two |
| lines of development reconverge is called a "merge". The commit |
| representing a merge can therefore have more than one parent, with |
| each parent representing the most recent commit on one of the lines |
| of development leading to that point.</p><p>The best way to see how this works is using the <a href="gitk.html" target="_top">gitk(1)</a> |
| command; running gitk now on a git repository and looking for merge |
| commits will help understand how the git organizes history.</p><p>In the following, we say that commit X is "reachable" from commit Y |
| if commit X is an ancestor of commit Y. Equivalently, you could say |
| that Y is a descendent of X, or that there is a chain of parents |
| leading from commit Y to commit X.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id273537"></a>Understanding history: History diagrams</h3></div></div></div><p>We will sometimes represent git history using diagrams like the one |
| below. Commits are shown as "o", and the links between them with |
| lines drawn with - / and \. Time goes left to right:</p><pre class="literallayout"> o--o--o <-- Branch A |
| / |
| o--o--o <-- master |
| o--o--o <-- Branch B</pre><p>If we need to talk about a particular commit, the character "o" may |
| be replaced with another letter or number.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id273565"></a>Understanding history: What is a branch?</h3></div></div></div><p>Though we've been using the word "branch" to mean a kind of reference |
| to a particular commit, the word branch is also commonly used to |
| refer to the line of commits leading up to that point. In the |
| example above, git may think of the branch named "A" as just a |
| pointer to one particular commit, but we may refer informally to the |
| line of three commits leading up to that point as all being part of |
| "branch A".</p><p>If we need to make it clear that we're just talking about the most |
| recent commit on the branch, we may refer to that commit as the |
| "head" of the branch.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id232302"></a>Manipulating branches</h2></div></div></div><p>Creating, deleting, and modifying branches is quick and easy; here's |
| a summary of the commands:</p><div class="variablelist"><dl><dt><span class="term"> |
| git branch |
| </span></dt><dd> |
| list all branches |
| </dd><dt><span class="term"> |
| git branch <branch> |
| </span></dt><dd> |
| create a new branch named <branch>, referencing the same |
| point in history as the current branch |
| </dd><dt><span class="term"> |
| git branch <branch> <start-point> |
| </span></dt><dd> |
| create a new branch named <branch>, referencing |
| <start-point>, which may be specified any way you like, |
| including using a branch name or a tag name |
| </dd><dt><span class="term"> |
| git branch -d <branch> |
| </span></dt><dd> |
| delete the branch <branch>; if the branch you are deleting |
| points to a commit which is not reachable from this branch, |
| this command will fail with a warning. |
| </dd><dt><span class="term"> |
| git branch -D <branch> |
| </span></dt><dd> |
| even if the branch points to a commit not reachable |
| from the current branch, you may know that that commit |
| is still reachable from some other branch or tag. In that |
| case it is safe to use this command to force git to delete |
| the branch. |
| </dd><dt><span class="term"> |
| git checkout <branch> |
| </span></dt><dd> |
| make the current branch <branch>, updating the working |
| directory to reflect the version referenced by <branch> |
| </dd><dt><span class="term"> |
| git checkout -b <new> <start-point> |
| </span></dt><dd> |
| create a new branch <new> referencing <start-point>, and |
| check it out. |
| </dd></dl></div><p>It is also useful to know that the special symbol "HEAD" can always |
| be used to refer to the current branch.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id273789"></a>Examining branches from a remote repository</h2></div></div></div><p>The "master" branch that was created at the time you cloned is a copy |
| of the HEAD in the repository that you cloned from. That repository |
| may also have had other branches, though, and your local repository |
| keeps branches which track each of those remote branches, which you |
| can view using the "-r" option to <a href="git-branch.html" target="_top">git-branch(1)</a>:</p><div class="literallayout"><p>$ git branch -r<br> |
| origin/HEAD<br> |
| origin/html<br> |
| origin/maint<br> |
| origin/man<br> |
| origin/master<br> |
| origin/next<br> |
| origin/pu<br> |
| origin/todo</p></div><p>You cannot check out these remote-tracking branches, but you can |
| examine them on a branch of your own, just as you would a tag:</p><div class="literallayout"><p>$ git checkout -b my-todo-copy origin/todo</p></div><p>Note that the name "origin" is just the name that git uses by default |
| to refer to the repository that you cloned from.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-git-stores-references"></a>Naming branches, tags, and other references</h2></div></div></div><p>Branches, remote-tracking branches, and tags are all references to |
| commits. All references are named with a slash-separated path name |
| starting with "refs"; the names we've been using so far are actually |
| shorthand:</p><div class="itemizedlist"><ul type="disc"><li> |
| The branch "test" is short for "refs/heads/test". |
| </li><li> |
| The tag "v2.6.18" is short for "refs/tags/v2.6.18". |
| </li><li> |
| "origin/master" is short for "refs/remotes/origin/master". |
| </li></ul></div><p>The full name is occasionally useful if, for example, there ever |
| exists a tag and a branch with the same name.</p><p>As another useful shortcut, if the repository "origin" posesses only |
| a single branch, you can refer to that branch as just "origin".</p><p>More generally, if you have defined a remote repository named |
| "example", you can refer to the branch in that repository as |
| "example". And for a repository with multiple branches, this will |
| refer to the branch designated as the "HEAD" branch.</p><p>For the complete list of paths which git checks for references, and |
| the order it uses to decide which to choose when there are multiple |
| references with the same shorthand name, see the "SPECIFYING |
| REVISIONS" section of <a href="git-rev-parse.html" target="_top">git-rev-parse(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="Updating-a-repository-with-git-fetch"></a>Updating a repository with git fetch</h2></div></div></div><p>Eventually the developer cloned from will do additional work in her |
| repository, creating new commits and advancing the branches to point |
| at the new commits.</p><p>The command "git fetch", with no arguments, will update all of the |
| remote-tracking branches to the latest version found in her |
| repository. It will not touch any of your own branches—not even the |
| "master" branch that was created for you on clone.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274034"></a>Fetching branches from other repositories</h2></div></div></div><p>You can also track branches from repositories other than the one you |
| cloned from, using <a href="git-remote.html" target="_top">git-remote(1)</a>:</p><div class="literallayout"><p>$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git<br> |
| $ git fetch<br> |
| * refs/remotes/linux-nfs/master: storing branch 'master' ...<br> |
| commit: bf81b46</p></div><p>New remote-tracking branches will be stored under the shorthand name |
| that you gave "git remote add", in this case linux-nfs:</p><div class="literallayout"><p>$ git branch -r<br> |
| linux-nfs/master<br> |
| origin/master</p></div><p>If you run "git fetch <remote>" later, the tracking branches for the |
| named <remote> will be updated.</p><p>If you examine the file .git/config, you will see that git has added |
| a new stanza:</p><div class="literallayout"><p>$ cat .git/config<br> |
| ...<br> |
| [remote "linux-nfs"]<br> |
| url = git://linux-nfs.org/~bfields/git.git<br> |
| fetch = +refs/heads/*:refs/remotes/linux-nfs-read/*<br> |
| ...</p></div><p>This is what causes git to track the remote's branches; you may modify |
| or delete these configuration options by editing .git/config with a |
| text editor. (See the "CONFIGURATION FILE" section of |
| <a href="git-config.html" target="_top">git-config(1)</a> for details.)</p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id274109"></a>Chapter 3. Exploring git history</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id274131">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#id274250">Naming commits</a></span></dt><dt><span class="section"><a href="#id274501">Creating tags</a></span></dt><dt><span class="section"><a href="#id274536">Browsing revisions</a></span></dt><dt><span class="section"><a href="#id274610">Generating diffs</a></span></dt><dt><span class="section"><a href="#id274653">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#id274679">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#id274685">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#id274738">Find first tagged version including a given fix</a></span></dt></dl></dd></dl></div><p>Git is best thought of as a tool for storing the history of a |
| collection of files. It does this by storing compressed snapshots of |
| the contents of a file heirarchy, together with "commits" which show |
| the relationships between these snapshots.</p><p>Git provides extremely flexible and fast tools for exploring the |
| history of a project.</p><p>We start with one specialized tool that is useful for finding the |
| commit that introduced a bug into a project.</p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274131"></a>How to use bisect to find a regression</h2></div></div></div><p>Suppose version 2.6.18 of your project worked, but the version at |
| "master" crashes. Sometimes the best way to find the cause of such a |
| regression is to perform a brute-force search through the project's |
| history to find the particular commit that caused the problem. The |
| <a href="git-bisect.html" target="_top">git-bisect(1)</a> command can help you do this:</p><div class="literallayout"><p>$ git bisect start<br> |
| $ git bisect good v2.6.18<br> |
| $ git bisect bad master<br> |
| Bisecting: 3537 revisions left to test after this<br> |
| [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]</p></div><p>If you run "git branch" at this point, you'll see that git has |
| temporarily moved you to a new branch named "bisect". This branch |
| points to a commit (with commit id 65934…) that is reachable from |
| v2.6.19 but not from v2.6.18. Compile and test it, and see whether |
| it crashes. Assume it does crash. Then:</p><div class="literallayout"><p>$ git bisect bad<br> |
| Bisecting: 1769 revisions left to test after this<br> |
| [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings</p></div><p>checks out an older version. Continue like this, telling git at each |
| stage whether the version it gives you is good or bad, and notice |
| that the number of revisions left to test is cut approximately in |
| half each time.</p><p>After about 13 tests (in this case), it will output the commit id of |
| the guilty commit. You can then examine the commit with |
| <a href="git-show.html" target="_top">git-show(1)</a>, find out who wrote it, and mail them your bug |
| report with the commit id. Finally, run</p><div class="literallayout"><p>$ git bisect reset</p></div><p>to return you to the branch you were on before and delete the |
| temporary "bisect" branch.</p><p>Note that the version which git-bisect checks out for you at each |
| point is just a suggestion, and you're free to try a different |
| version if you think it would be a good idea. For example, |
| occasionally you may land on a commit that broke something unrelated; |
| run</p><div class="literallayout"><p>$ git bisect-visualize</p></div><p>which will run gitk and label the commit it chose with a marker that |
| says "bisect". Chose a safe-looking commit nearby, note its commit |
| id, and check it out with:</p><div class="literallayout"><p>$ git reset --hard fb47ddb2db...</p></div><p>then test, run "bisect good" or "bisect bad" as appropriate, and |
| continue.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274250"></a>Naming commits</h2></div></div></div><p>We have seen several ways of naming commits already:</p><div class="itemizedlist"><ul type="disc"><li> |
| 40-hexdigit object name |
| </li><li> |
| branch name: refers to the commit at the head of the given |
| branch |
| </li><li> |
| tag name: refers to the commit pointed to by the given tag |
| (we've seen branches and tags are special cases of |
| <a href="#how-git-stores-references" title="Naming branches, tags, and other references">references</a>). |
| </li><li> |
| HEAD: refers to the head of the current branch |
| </li></ul></div><p>There are many more; see the "SPECIFYING REVISIONS" section of the |
| <a href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> man page for the complete list of ways to |
| name revisions. Some examples:</p><div class="literallayout"><p>$ git show fb47ddb2 # the first few characters of the object name<br> |
| # are usually enough to specify it uniquely<br> |
| $ git show HEAD^ # the parent of the HEAD commit<br> |
| $ git show HEAD^^ # the grandparent<br> |
| $ git show HEAD~4 # the great-great-grandparent</p></div><p>Recall that merge commits may have more than one parent; by default, |
| ^ and ~ follow the first parent listed in the commit, but you can |
| also choose:</p><div class="literallayout"><p>$ git show HEAD^1 # show the first parent of HEAD<br> |
| $ git show HEAD^2 # show the second parent of HEAD</p></div><p>In addition to HEAD, there are several other special names for |
| commits:</p><p>Merges (to be discussed later), as well as operations such as |
| git-reset, which change the currently checked-out commit, generally |
| set ORIG_HEAD to the value HEAD had before the current operation.</p><p>The git-fetch operation always stores the head of the last fetched |
| branch in FETCH_HEAD. For example, if you run git fetch without |
| specifying a local branch as the target of the operation</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git theirbranch</p></div><p>the fetched commits will still be available from FETCH_HEAD.</p><p>When we discuss merges we'll also see the special name MERGE_HEAD, |
| which refers to the other branch that we're merging in to the current |
| branch.</p><p>The <a href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> command is a low-level command that is |
| occasionally useful for translating some name for a commit to the object |
| name for that commit:</p><div class="literallayout"><p>$ git rev-parse origin<br> |
| e05db0fd4f31dde7005f075a84f96b360d05984b</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274501"></a>Creating tags</h2></div></div></div><p>We can also create a tag to refer to a particular commit; after |
| running</p><div class="literallayout"><p>$ git-tag stable-1 1b2e1d63ff</p></div><p>You can use stable-1 to refer to the commit 1b2e1d63ff.</p><p>This creates a "lightweight" tag. If the tag is a tag you wish to |
| share with others, and possibly sign cryptographically, then you |
| should create a tag object instead; see the <a href="git-tag.html" target="_top">git-tag(1)</a> man |
| page for details.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274536"></a>Browsing revisions</h2></div></div></div><p>The <a href="git-log.html" target="_top">git-log(1)</a> command can show lists of commits. On its |
| own, it shows all commits reachable from the parent commit; but you |
| can also make more specific requests:</p><div class="literallayout"><p>$ git log v2.5.. # commits since (not reachable from) v2.5<br> |
| $ git log test..master # commits reachable from master but not test<br> |
| $ git log master..test # ...reachable from test but not master<br> |
| $ git log master...test # ...reachable from either test or master,<br> |
| # but not both<br> |
| $ git log --since="2 weeks ago" # commits from the last 2 weeks<br> |
| $ git log Makefile # commits which modify Makefile<br> |
| $ git log fs/ # ... which modify any file under fs/<br> |
| $ git log -S'foo()' # commits which add or remove any file data<br> |
| # matching the string 'foo()'</p></div><p>And of course you can combine all of these; the following finds |
| commits since v2.5 which touch the Makefile or any file under fs:</p><div class="literallayout"><p>$ git log v2.5.. Makefile fs/</p></div><p>You can also ask git log to show patches:</p><div class="literallayout"><p>$ git log -p</p></div><p>See the "—pretty" option in the <a href="git-log.html" target="_top">git-log(1)</a> man page for more |
| display options.</p><p>Note that git log starts with the most recent commit and works |
| backwards through the parents; however, since git history can contain |
| multiple independent lines of development, the particular order that |
| commits are listed in may be somewhat arbitrary.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274610"></a>Generating diffs</h2></div></div></div><p>You can generate diffs between any two versions using |
| <a href="git-diff.html" target="_top">git-diff(1)</a>:</p><div class="literallayout"><p>$ git diff master..test</p></div><p>Sometimes what you want instead is a set of patches:</p><div class="literallayout"><p>$ git format-patch master..test</p></div><p>will generate a file with a patch for each commit reachable from test |
| but not from master. Note that if master also has commits which are |
| not reachable from test, then the combined result of these patches |
| will not be the same as the diff produced by the git-diff example.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274653"></a>Viewing old file versions</h2></div></div></div><p>You can always view an old version of a file by just checking out the |
| correct revision first. But sometimes it is more convenient to be |
| able to view an old version of a single file without checking |
| anything out; this command does that:</p><div class="literallayout"><p>$ git show v2.5:fs/locks.c</p></div><p>Before the colon may be anything that names a commit, and after it |
| may be any path to a file tracked by git.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274679"></a>Examples</h2></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id274685"></a>Check whether two branches point at the same history</h3></div></div></div><p>Suppose you want to check whether two branches point at the same point |
| in history.</p><div class="literallayout"><p>$ git diff origin..master</p></div><p>will tell you whether the contents of the project are the same at the |
| two branches; in theory, however, it's possible that the same project |
| contents could have been arrived at by two different historical |
| routes. You could compare the object names:</p><div class="literallayout"><p>$ git rev-list origin<br> |
| e05db0fd4f31dde7005f075a84f96b360d05984b<br> |
| $ git rev-list master<br> |
| e05db0fd4f31dde7005f075a84f96b360d05984b</p></div><p>Or you could recall that the … operator selects all commits |
| contained reachable from either one reference or the other but not |
| both: so</p><div class="literallayout"><p>$ git log origin...master</p></div><p>will return no commits when the two branches are equal.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id274738"></a>Find first tagged version including a given fix</h3></div></div></div><p>Suppose you know that the commit e05db0fd fixed a certain problem. |
| You'd like to find the earliest tagged release that contains that |
| fix.</p><p>Of course, there may be more than one answer—if the history branched |
| after commit e05db0fd, then there could be multiple "earliest" tagged |
| releases.</p><p>You could just visually inspect the commits since e05db0fd:</p><div class="literallayout"><p>$ gitk e05db0fd..</p></div><p>Or you can use <a href="git-name-rev.html" target="_top">git-name-rev(1)</a>, which will give the commit a |
| name based on any tag it finds pointing to one of the commit's |
| descendants:</p><div class="literallayout"><p>$ git name-rev e05db0fd<br> |
| e05db0fd tags/v1.5.0-rc1^0~23</p></div><p>The <a href="git-describe.html" target="_top">git-describe(1)</a> command does the opposite, naming the |
| revision using a tag on which the given commit is based:</p><div class="literallayout"><p>$ git describe e05db0fd<br> |
| v1.5.0-rc0-ge05db0f</p></div><p>but that may sometimes help you guess which tags might come after the |
| given commit.</p><p>If you just want to verify whether a given tagged version contains a |
| given commit, you could use <a href="git-merge-base.html" target="_top">git-merge-base(1)</a>:</p><div class="literallayout"><p>$ git merge-base e05db0fd v1.5.0-rc1<br> |
| e05db0fd4f31dde7005f075a84f96b360d05984b</p></div><p>The merge-base command finds a common ancestor of the given commits, |
| and always returns one or the other in the case where one is a |
| descendant of the other; so the above output shows that e05db0fd |
| actually is an ancestor of v1.5.0-rc1.</p><p>Alternatively, note that</p><div class="literallayout"><p>$ git log v1.5.0-rc1..e05db0fd</p></div><p>will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, |
| because it outputs only commits that are not reachable from v1.5.0-rc1.</p><p>As yet another alternative, the <a href="git-show-branch.html" target="_top">git-show-branch(1)</a> command lists |
| the commits reachable from its arguments with a display on the left-hand |
| side that indicates which arguments that commit is reachable from. So, |
| you can run something like</p><div class="literallayout"><p>$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2<br> |
| ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if<br> |
| available<br> |
| ! [v1.5.0-rc0] GIT v1.5.0 preview<br> |
| ! [v1.5.0-rc1] GIT v1.5.0-rc1<br> |
| ! [v1.5.0-rc2] GIT v1.5.0-rc2<br> |
| ...</p></div><p>then search for a line that looks like</p><div class="literallayout"><p>+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if<br> |
| available</p></div><p>Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and |
| from v1.5.0-rc2, but not from v1.5.0-rc0.</p></div></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id274901"></a>Chapter 4. Developing with git</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id274907">Telling git your name</a></span></dt><dt><span class="section"><a href="#id274939">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">how to make a commit</a></span></dt><dt><span class="section"><a href="#id275166">creating good commit messages</a></span></dt><dt><span class="section"><a href="#id275182">how to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dt><span class="section"><a href="#undoing-a-merge">undoing a merge</a></span></dt><dt><span class="section"><a href="#id275418">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#id275447">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#id275500">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#id275558">Fixing a mistake by editing history</a></span></dt><dt><span class="section"><a href="#id275628">Checking out an old version of a file</a></span></dt></dl></dd><dt><span class="section"><a href="#id275687">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#id275724">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#id275730">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#id275805">Recovering lost changes</a></span></dt></dl></dd></dl></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274907"></a>Telling git your name</h2></div></div></div><p>Before creating any commits, you should introduce yourself to git. The |
| easiest way to do so is:</p><div class="literallayout"><p>$ cat >~/.gitconfig <<\EOF<br> |
| [user]<br> |
| name = Your Name Comes Here<br> |
| email = you@yourdomain.example.com<br> |
| EOF</p></div><p>(See the "CONFIGURATION FILE" section of <a href="git-config.html" target="_top">git-config(1)</a> for |
| details on the configuration file.)</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id274939"></a>Creating a new repository</h2></div></div></div><p>Creating a new repository from scratch is very easy:</p><div class="literallayout"><p>$ mkdir project<br> |
| $ cd project<br> |
| $ git init</p></div><p>If you have some initial content (say, a tarball):</p><div class="literallayout"><p>$ tar -xzvf project.tar.gz<br> |
| $ cd project<br> |
| $ git init<br> |
| $ git add . # include everything below ./ in the first commit:<br> |
| $ git commit</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-make-a-commit"></a>how to make a commit</h2></div></div></div><p>Creating a new commit takes three steps:</p><div class="orderedlist"><ol type="1"><li> |
| Making some changes to the working directory using your |
| favorite editor. |
| </li><li> |
| Telling git about your changes. |
| </li><li> |
| Creating the commit using the content you told git about |
| in step 2. |
| </li></ol></div><p>In practice, you can interleave and repeat steps 1 and 2 as many |
| times as you want: in order to keep track of what you want committed |
| at step 3, git maintains a snapshot of the tree's contents in a |
| special staging area called "the index."</p><p>At the beginning, the content of the index will be identical to |
| that of the HEAD. The command "git diff —cached", which shows |
| the difference between the HEAD and the index, should therefore |
| produce no output at that point.</p><p>Modifying the index is easy:</p><p>To update the index with the new contents of a modified file, use</p><div class="literallayout"><p>$ git add path/to/file</p></div><p>To add the contents of a new file to the index, use</p><div class="literallayout"><p>$ git add path/to/file</p></div><p>To remove a file from the index and from the working tree,</p><div class="literallayout"><p>$ git rm path/to/file</p></div><p>After each step you can verify that</p><div class="literallayout"><p>$ git diff --cached</p></div><p>always shows the difference between the HEAD and the index file—this |
| is what you'd commit if you created the commit now—and that</p><div class="literallayout"><p>$ git diff</p></div><p>shows the difference between the working tree and the index file.</p><p>Note that "git add" always adds just the current contents of a file |
| to the index; further changes to the same file will be ignored unless |
| you run git-add on the file again.</p><p>When you're ready, just run</p><div class="literallayout"><p>$ git commit</p></div><p>and git will prompt you for a commit message and then create the new |
| commit. Check to make sure it looks like what you expected with</p><div class="literallayout"><p>$ git show</p></div><p>As a special shortcut,</p><div class="literallayout"><p>$ git commit -a</p></div><p>will update the index with any files that you've modified or removed |
| and create a commit, all in one step.</p><p>A number of commands are useful for keeping track of what you're |
| about to commit:</p><div class="literallayout"><p>$ git diff --cached # difference between HEAD and the index; what<br> |
| # would be commited if you ran "commit" now.<br> |
| $ git diff # difference between the index file and your<br> |
| # working directory; changes that would not<br> |
| # be included if you ran "commit" now.<br> |
| $ git status # a brief per-file summary of the above.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id275166"></a>creating good commit messages</h2></div></div></div><p>Though not required, it's a good idea to begin the commit message |
| with a single short (less than 50 character) line summarizing the |
| change, followed by a blank line and then a more thorough |
| description. Tools that turn commits into email, for example, use |
| the first line on the Subject line and the rest of the commit in the |
| body.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id275182"></a>how to merge</h2></div></div></div><p>You can rejoin two diverging branches of development using |
| <a href="git-merge.html" target="_top">git-merge(1)</a>:</p><div class="literallayout"><p>$ git merge branchname</p></div><p>merges the development in the branch "branchname" into the current |
| branch. If there are conflicts—for example, if the same file is |
| modified in two different ways in the remote branch and the local |
| branch—then you are warned; the output may look something like this:</p><div class="literallayout"><p>$ git pull . next<br> |
| Trying really trivial in-index merge...<br> |
| fatal: Merge requires file-level merging<br> |
| Nope.<br> |
| Merging HEAD with 77976da35a11db4580b80ae27e8d65caf5208086<br> |
| Merging:<br> |
| 15e2162 world<br> |
| 77976da goodbye<br> |
| found 1 common ancestor(s):<br> |
| d122ed4 initial<br> |
| Auto-merging file.txt<br> |
| CONFLICT (content): Merge conflict in file.txt<br> |
| Automatic merge failed; fix conflicts and then commit the result.</p></div><p>Conflict markers are left in the problematic files, and after |
| you resolve the conflicts manually, you can update the index |
| with the contents and run git commit, as you normally would when |
| creating a new file.</p><p>If you examine the resulting commit using gitk, you will see that it |
| has two parents, one pointing to the top of the current branch, and |
| one to the top of the other branch.</p><p>In more detail:</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="resolving-a-merge"></a>Resolving a merge</h2></div></div></div><p>When a merge isn't resolved automatically, git leaves the index and |
| the working tree in a special state that gives you all the |
| information you need to help resolve the merge.</p><p>Files with conflicts are marked specially in the index, so until you |
| resolve the problem and update the index, git commit will fail:</p><div class="literallayout"><p>$ git commit<br> |
| file.txt: needs merge</p></div><p>Also, git status will list those files as "unmerged".</p><p>All of the changes that git was able to merge automatically are |
| already added to the index file, so <a href="git-diff.html" target="_top">git-diff(1)</a> shows only |
| the conflicts. Also, it uses a somewhat unusual syntax:</p><div class="literallayout"><p>$ git diff<br> |
| diff --cc file.txt<br> |
| index 802992c,2b60207..0000000<br> |
| --- a/file.txt<br> |
| +++ b/file.txt<br> |
| @@@ -1,1 -1,1 +1,5 @@@<br> |
| ++<<<<<<< HEAD:file.txt<br> |
| +Hello world<br> |
| ++=======<br> |
| + Goodbye<br> |
| ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</p></div><p>Recall that the commit which will be commited after we resolve this |
| conflict will have two parents instead of the usual one: one parent |
| will be HEAD, the tip of the current branch; the other will be the |
| tip of the other branch, which is stored temporarily in MERGE_HEAD.</p><p>The diff above shows the differences between the working-tree version |
| of file.txt and two previous versions: one version from HEAD, and one |
| from MERGE_HEAD. So instead of preceding each line by a single "+" |
| or "-", it now uses two columns: the first column is used for |
| differences between the first parent and the working directory copy, |
| and the second for differences between the second parent and the |
| working directory copy. Thus after resolving the conflict in the |
| obvious way, the diff will look like:</p><div class="literallayout"><p>$ git diff<br> |
| diff --cc file.txt<br> |
| index 802992c,2b60207..0000000<br> |
| --- a/file.txt<br> |
| +++ b/file.txt<br> |
| @@@ -1,1 -1,1 +1,1 @@@<br> |
| - Hello world<br> |
| -Goodbye<br> |
| ++Goodbye world</p></div><p>This shows that our resolved version deleted "Hello world" from the |
| first parent, deleted "Goodbye" from the second parent, and added |
| "Goodbye world", which was previously absent from both.</p><p>The <a href="git-log.html" target="_top">git-log(1)</a> command also provides special help for merges:</p><div class="literallayout"><p>$ git log --merge</p></div><p>This will list all commits which exist only on HEAD or on MERGE_HEAD, |
| and which touch an unmerged file.</p><p>We can now add the resolved version to the index and commit:</p><div class="literallayout"><p>$ git add file.txt<br> |
| $ git commit</p></div><p>Note that the commit message will already be filled in for you with |
| some information about the merge. Normally you can just use this |
| default message unchanged, but you may add additional commentary of |
| your own if desired.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="undoing-a-merge"></a>undoing a merge</h2></div></div></div><p>If you get stuck and decide to just give up and throw the whole mess |
| away, you can always return to the pre-merge state with</p><div class="literallayout"><p>$ git reset --hard HEAD</p></div><p>Or, if you've already commited the merge that you want to throw away,</p><div class="literallayout"><p>$ git reset --hard HEAD^</p></div><p>However, this last command can be dangerous in some cases—never |
| throw away a commit you have already committed if that commit may |
| itself have been merged into another branch, as doing so may confuse |
| further merges.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id275418"></a>Fast-forward merges</h2></div></div></div><p>There is one special case not mentioned above, which is treated |
| differently. Normally, a merge results in a merge commit, with two |
| parents, one pointing at each of the two lines of development that |
| were merged.</p><p>However, if one of the two lines of development is completely |
| contained within the other—so every commit present in the one is |
| already contained in the other—then git just performs a |
| <a href="#fast-forwards" title="Understanding git history: fast-forwards">fast forward</a>; the head of the current branch is |
| moved forward to point at the head of the merged-in branch, without |
| any new commits being created.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id275447"></a>Fixing mistakes</h2></div></div></div><p>If you've messed up the working tree, but haven't yet committed your |
| mistake, you can return the entire working tree to the last committed |
| state with</p><div class="literallayout"><p>$ git reset --hard HEAD</p></div><p>If you make a commit that you later wish you hadn't, there are two |
| fundamentally different ways to fix the problem:</p><div class="orderedlist"><ol type="1"><li> |
| You can create a new commit that undoes whatever was done |
| by the previous commit. This is the correct thing if your |
| mistake has already been made public. |
| </li><li> |
| You can go back and modify the old commit. You should |
| never do this if you have already made the history public; |
| git does not normally expect the "history" of a project to |
| change, and cannot correctly perform repeated merges from |
| a branch that has had its history changed. |
| </li></ol></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id275500"></a>Fixing a mistake with a new commit</h3></div></div></div><p>Creating a new commit that reverts an earlier change is very easy; |
| just pass the <a href="git-revert.html" target="_top">git-revert(1)</a> command a reference to the bad |
| commit; for example, to revert the most recent commit:</p><div class="literallayout"><p>$ git revert HEAD</p></div><p>This will create a new commit which undoes the change in HEAD. You |
| will be given a chance to edit the commit message for the new commit.</p><p>You can also revert an earlier change, for example, the next-to-last:</p><div class="literallayout"><p>$ git revert HEAD^</p></div><p>In this case git will attempt to undo the old change while leaving |
| intact any changes made since then. If more recent changes overlap |
| with the changes to be reverted, then you will be asked to fix |
| conflicts manually, just as in the case of <a href="#resolving-a-merge" title="Resolving a merge">resolving a merge</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id275558"></a>Fixing a mistake by editing history</h3></div></div></div><p>If the problematic commit is the most recent commit, and you have not |
| yet made that commit public, then you may just |
| <a href="#undoing-a-merge" title="undoing a merge">destroy it using git-reset</a>.</p><p>Alternatively, you |
| can edit the working directory and update the index to fix your |
| mistake, just as if you were going to <a href="#how-to-make-a-commit" title="how to make a commit">create a new commit</a>, then run</p><div class="literallayout"><p>$ git commit --amend</p></div><p>which will replace the old commit by a new commit incorporating your |
| changes, giving you a chance to edit the old commit message first.</p><p>Again, you should never do this to a commit that may already have |
| been merged into another branch; use <a href="git-revert.html" target="_top">git-revert(1)</a> instead in |
| that case.</p><p>It is also possible to edit commits further back in the history, but |
| this is an advanced topic to be left for |
| <a href="#cleaning-up-history" title="Chapter 6. Rewriting history and maintaining patch series">another chapter</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id275628"></a>Checking out an old version of a file</h3></div></div></div><p>In the process of undoing a previous bad change, you may find it |
| useful to check out an older version of a particular file using |
| <a href="git-checkout.html" target="_top">git-checkout(1)</a>. We've used git checkout before to switch |
| branches, but it has quite different behavior if it is given a path |
| name: the command</p><div class="literallayout"><p>$ git checkout HEAD^ path/to/file</p></div><p>replaces path/to/file by the contents it had in the commit HEAD^, and |
| also updates the index to match. It does not change branches.</p><p>If you just want to look at an old version of the file, without |
| modifying the working directory, you can do that with |
| <a href="git-show.html" target="_top">git-show(1)</a>:</p><div class="literallayout"><p>$ git show HEAD^ path/to/file</p></div><p>which will display the given version of the file.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id275687"></a>Ensuring good performance</h2></div></div></div><p>On large repositories, git depends on compression to keep the history |
| information from taking up to much space on disk or in memory.</p><p>This compression is not performed automatically. Therefore you |
| should occasionally run <a href="git-gc.html" target="_top">git-gc(1)</a>:</p><div class="literallayout"><p>$ git gc</p></div><p>to recompress the archive. This can be very time-consuming, so |
| you may prefer to run git-gc when you are not doing other work.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id275724"></a>Ensuring reliability</h2></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id275730"></a>Checking the repository for corruption</h3></div></div></div><p>The <a href="git-fsck.html" target="_top">git-fsck(1)</a> command runs a number of self-consistency checks |
| on the repository, and reports on any problems. This may take some |
| time. The most common warning by far is about "dangling" objects:</p><div class="literallayout"><p>$ git fsck<br> |
| dangling commit 7281251ddd2a61e38657c827739c57015671a6b3<br> |
| dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63<br> |
| dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5<br> |
| dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb<br> |
| dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f<br> |
| dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e<br> |
| dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085<br> |
| dangling tree b24c2473f1fd3d91352a624795be026d64c8841f<br> |
| ...</p></div><p>Dangling objects are objects that are harmless, but also unnecessary; |
| you can remove them at any time with <a href="git-prune.html" target="_top">git-prune(1)</a> or the —prune |
| option to <a href="git-gc.html" target="_top">git-gc(1)</a>:</p><div class="literallayout"><p>$ git gc --prune</p></div><p>This may be time-consuming. Unlike most other git operations (including |
| git-gc when run without any options), it is not safe to prune while |
| other git operations are in progress in the same repository.</p><p>For more about dangling objects, see <a href="#dangling-objects" title="Dangling objects">the section called “Dangling objects”</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id275805"></a>Recovering lost changes</h3></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id275811"></a>Reflogs</h4></div></div></div><p>Say you modify a branch with <a href="git-reset.html" target="_top">git-reset(1)</a> —hard, and then |
| realize that the branch was the only reference you had to that point in |
| history.</p><p>Fortunately, git also keeps a log, called a "reflog", of all the |
| previous values of each branch. So in this case you can still find the |
| old history using, for example,</p><div class="literallayout"><p>$ git log master@{1}</p></div><p>This lists the commits reachable from the previous version of the head. |
| This syntax can be used to with any git command that accepts a commit, |
| not just with git log. Some other examples:</p><div class="literallayout"><p>$ git show master@{2} # See where the branch pointed 2,<br> |
| $ git show master@{3} # 3, ... changes ago.<br> |
| $ gitk master@{yesterday} # See where it pointed yesterday,<br> |
| $ gitk master@{"1 week ago"} # ... or last week</p></div><p>The reflogs are kept by default for 30 days, after which they may be |
| pruned. See <a href="git-reflog.html" target="_top">git-reflog(1)</a> and <a href="git-gc.html" target="_top">git-gc(1)</a> to learn |
| how to control this pruning, and see the "SPECIFYING REVISIONS" |
| section of <a href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> for details.</p><p>Note that the reflog history is very different from normal git history. |
| While normal history is shared by every repository that works on the |
| same project, the reflog history is not shared: it tells you only about |
| how the branches in your local repository have changed over time.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id275889"></a>Examining dangling objects</h4></div></div></div><p>In some situations the reflog may not be able to save you. For |
| example, suppose you delete a branch, then realize you need the history |
| it contained. The reflog is also deleted; however, if you have not |
| yet pruned the repository, then you may still be able to find |
| the lost commits; run git-fsck and watch for output that mentions |
| "dangling commits":</p><div class="literallayout"><p>$ git fsck<br> |
| dangling commit 7281251ddd2a61e38657c827739c57015671a6b3<br> |
| dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63<br> |
| dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5<br> |
| ...</p></div><p>You can examine |
| one of those dangling commits with, for example,</p><div class="literallayout"><p>$ gitk 7281251ddd --not --all</p></div><p>which does what it sounds like: it says that you want to see the commit |
| history that is described by the dangling commit(s), but not the |
| history that is described by all your existing branches and tags. Thus |
| you get exactly the history reachable from that commit that is lost. |
| (And notice that it might not be just one commit: we only report the |
| "tip of the line" as being dangling, but there might be a whole deep |
| and complex commit history that was dropped.)</p><p>If you decide you want the history back, you can always create a new |
| reference pointing to it, for example, a new branch:</p><div class="literallayout"><p>$ git branch recovered-branch 7281251ddd</p></div></div></div></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id275955"></a>Chapter 5. Sharing development with others</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#getting-updates-with-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#id276086">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#id276136">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via http</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a git repository via the git protocol</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#id276548">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#id276567">Allow web browsing of a repository</a></span></dt><dt><span class="section"><a href="#id276579">Examples</a></span></dt></dl></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="getting-updates-with-git-pull"></a>Getting updates with git pull</h2></div></div></div><p>After you clone a repository and make a few changes of your own, you |
| may wish to check the original repository for updates and merge them |
| into your own work.</p><p>We have already seen <a href="#Updating-a-repository-with-git-fetch" title="Updating a repository with git fetch">how to keep remote tracking branches up to date</a> with <a href="git-fetch.html" target="_top">git-fetch(1)</a>, |
| and how to merge two branches. So you can merge in changes from the |
| original repository's master branch with:</p><div class="literallayout"><p>$ git fetch<br> |
| $ git merge origin/master</p></div><p>However, the <a href="git-pull.html" target="_top">git-pull(1)</a> command provides a way to do this in |
| one step:</p><div class="literallayout"><p>$ git pull origin master</p></div><p>In fact, "origin" is normally the default repository to pull from, |
| and the default branch is normally the HEAD of the remote repository, |
| so often you can accomplish the above with just</p><div class="literallayout"><p>$ git pull</p></div><p>See the descriptions of the branch.<name>.remote and |
| branch.<name>.merge options in <a href="git-config.html" target="_top">git-config(1)</a> to learn |
| how to control these defaults depending on the current branch.</p><p>In addition to saving you keystrokes, "git pull" also helps you by |
| producing a default commit message documenting the branch and |
| repository that you pulled from.</p><p>(But note that no such commit will be created in the case of a |
| <a href="#fast-forwards" title="Understanding git history: fast-forwards">fast forward</a>; instead, your branch will just be |
| updated to point to the latest commit from the upstream branch.)</p><p>The git-pull command can also be given "." as the "remote" repository, |
| in which case it just merges in a branch from the current repository; so |
| the commands</p><div class="literallayout"><p>$ git pull . branch<br> |
| $ git merge branch</p></div><p>are roughly equivalent. The former is actually very commonly used.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276086"></a>Submitting patches to a project</h2></div></div></div><p>If you just have a few changes, the simplest way to submit them may |
| just be to send them as patches in email:</p><p>First, use <a href="git-format-patch.html" target="_top">git-format-patch(1)</a>; for example:</p><div class="literallayout"><p>$ git format-patch origin</p></div><p>will produce a numbered series of files in the current directory, one |
| for each patch in the current branch but not in origin/HEAD.</p><p>You can then import these into your mail client and send them by |
| hand. However, if you have a lot to send at once, you may prefer to |
| use the <a href="git-send-email.html" target="_top">git-send-email(1)</a> script to automate the process. |
| Consult the mailing list for your project first to determine how they |
| prefer such patches be handled.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276136"></a>Importing patches to a project</h2></div></div></div><p>Git also provides a tool called <a href="git-am.html" target="_top">git-am(1)</a> (am stands for |
| "apply mailbox"), for importing such an emailed series of patches. |
| Just save all of the patch-containing messages, in order, into a |
| single mailbox file, say "patches.mbox", then run</p><div class="literallayout"><p>$ git am -3 patches.mbox</p></div><p>Git will apply each patch in order; if any conflicts are found, it |
| will stop, and you can fix the conflicts as described in |
| "<a href="#resolving-a-merge" title="Resolving a merge">Resolving a merge</a>". (The "-3" option tells |
| git to perform a merge; if you would prefer it just to abort and |
| leave your tree and index untouched, you may omit that option.)</p><p>Once the index is updated with the results of the conflict |
| resolution, instead of creating a new commit, just run</p><div class="literallayout"><p>$ git am --resolved</p></div><p>and git will create the commit for you and continue applying the |
| remaining patches from the mailbox.</p><p>The final result will be a series of commits, one for each patch in |
| the original mailbox, with authorship and commit log message each |
| taken from the message containing each patch.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="setting-up-a-public-repository"></a>Setting up a public repository</h2></div></div></div><p>Another way to submit changes to a project is to simply tell the |
| maintainer of that project to pull from your repository, exactly as |
| you did in the section "<a href="#getting-updates-with-git-pull" title="Getting updates with git pull">Getting updates with git pull</a>".</p><p>If you and maintainer both have accounts on the same machine, then |
| then you can just pull changes from each other's repositories |
| directly; note that all of the commands (<a href="git-clone.html" target="_top">git-clone(1)</a>, |
| git-fetch[1], git-pull[1], etc.) that accept a URL as an argument |
| will also accept a local file patch; so, for example, you can |
| use</p><div class="literallayout"><p>$ git clone /path/to/repository<br> |
| $ git pull /path/to/other/repository</p></div><p>If this sort of setup is inconvenient or impossible, another (more |
| common) option is to set up a public repository on a public server. |
| This also allows you to cleanly separate private work in progress |
| from publicly visible work.</p><p>You will continue to do your day-to-day work in your personal |
| repository, but periodically "push" changes from your personal |
| repository into your public repository, allowing other developers to |
| pull from that repository. So the flow of changes, in a situation |
| where there is one other developer with a public repository, looks |
| like this:</p><pre class="literallayout"> you push |
| your personal repo ------------------> your public repo |
| ^ | |
| | | |
| | you pull | they pull |
| | | |
| | | |
| | they push V |
| their public repo <------------------- their repo</pre><p>Now, assume your personal repository is in the directory ~/proj. We |
| first create a new clone of the repository:</p><div class="literallayout"><p>$ git clone --bare proj-clone.git</p></div><p>The resulting directory proj-clone.git will contains a "bare" git |
| repository—it is just the contents of the ".git" directory, without |
| a checked-out copy of a working directory.</p><p>Next, copy proj-clone.git to the server where you plan to host the |
| public repository. You can use scp, rsync, or whatever is most |
| convenient.</p><p>If somebody else maintains the public server, they may already have |
| set up a git service for you, and you may skip to the section |
| "<a href="#pushing-changes-to-a-public-repository" title="Pushing changes to a public repository">Pushing changes to a public repository</a>", below.</p><p>Otherwise, the following sections explain how to export your newly |
| created public repository:</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="exporting-via-http"></a>Exporting a git repository via http</h2></div></div></div><p>The git protocol gives better performance and reliability, but on a |
| host with a web server set up, http exports may be simpler to set up.</p><p>All you need to do is place the newly created bare git repository in |
| a directory that is exported by the web server, and make some |
| adjustments to give web clients some extra information they need:</p><div class="literallayout"><p>$ mv proj.git /home/you/public_html/proj.git<br> |
| $ cd proj.git<br> |
| $ git update-server-info<br> |
| $ chmod a+x hooks/post-update</p></div><p>(For an explanation of the last two lines, see |
| <a href="git-update-server-info.html" target="_top">git-update-server-info(1)</a>, and the documentation |
| <a href="hooks.txt" target="_top">Hooks used by git</a>.)</p><p>Advertise the url of proj.git. Anybody else should then be able to |
| clone or pull from that url, for example with a commandline like:</p><div class="literallayout"><p>$ git clone http://yourserver.com/~you/proj.git</p></div><p>(See also |
| <a href="howto/setup-git-server-over-http.txt" target="_top">setup-git-server-over-http</a> |
| for a slightly more sophisticated setup using WebDAV which also |
| allows pushing over http.)</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="exporting-via-git"></a>Exporting a git repository via the git protocol</h2></div></div></div><p>This is the preferred method.</p><p>For now, we refer you to the <a href="git-daemon.html" target="_top">git-daemon(1)</a> man page for |
| instructions. (See especially the examples section.)</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="pushing-changes-to-a-public-repository"></a>Pushing changes to a public repository</h2></div></div></div><p>Note that the two techniques outline above (exporting via |
| <a href="#exporting-via-http" title="Exporting a git repository via http">http</a> or <a href="#exporting-via-git" title="Exporting a git repository via the git protocol">git</a>) allow other |
| maintainers to fetch your latest changes, but they do not allow write |
| access, which you will need to update the public repository with the |
| latest changes created in your private repository.</p><p>The simplest way to do this is using <a href="git-push.html" target="_top">git-push(1)</a> and ssh; to |
| update the remote branch named "master" with the latest state of your |
| branch named "master", run</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git master:master</p></div><p>or just</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git master</p></div><p>As with git-fetch, git-push will complain if this does not result in |
| a <a href="#fast-forwards" title="Understanding git history: fast-forwards">fast forward</a>. Normally this is a sign of |
| something wrong. However, if you are sure you know what you're |
| doing, you may force git-push to perform the update anyway by |
| proceeding the branch name by a plus sign:</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git +master</p></div><p>As with git-fetch, you may also set up configuration options to |
| save typing; so, for example, after</p><div class="literallayout"><p>$ cat >.git/config <<EOF<br> |
| [remote "public-repo"]<br> |
| url = ssh://yourserver.com/~you/proj.git<br> |
| EOF</p></div><p>you should be able to perform the above push with just</p><div class="literallayout"><p>$ git push public-repo master</p></div><p>See the explanations of the remote.<name>.url, branch.<name>.remote, |
| and remote.<name>.push options in <a href="git-config.html" target="_top">git-config(1)</a> for |
| details.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276548"></a>Setting up a shared repository</h2></div></div></div><p>Another way to collaborate is by using a model similar to that |
| commonly used in CVS, where several developers with special rights |
| all push to and pull from a single shared repository. See |
| <a href="cvs-migration.txt" target="_top">git for CVS users</a> for instructions on how to |
| set this up.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276567"></a>Allow web browsing of a repository</h2></div></div></div><p>The gitweb cgi script provides users an easy way to browse your |
| project's files and history without having to install git; see the file |
| gitweb/README in the git source tree for instructions on setting it up.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276579"></a>Examples</h2></div></div></div><p>TODO: topic branches, typical roles as in everyday.txt, ?</p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="cleaning-up-history"></a>Chapter 6. Rewriting history and maintaining patch series</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id276611">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#id276686">Keeping a patch series up to date using git-rebase</a></span></dt><dt><span class="section"><a href="#id276817">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#id276878">Other tools</a></span></dt><dt><span class="section"><a href="#id276891">Problems with rewriting history</a></span></dt></dl></div><p>Normally commits are only added to a project, never taken away or |
| replaced. Git is designed with this assumption, and violating it will |
| cause git's merge machinery (for example) to do the wrong thing.</p><p>However, there is a situation in which it can be useful to violate this |
| assumption.</p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276611"></a>Creating the perfect patch series</h2></div></div></div><p>Suppose you are a contributor to a large project, and you want to add a |
| complicated feature, and to present it to the other developers in a way |
| that makes it easy for them to read your changes, verify that they are |
| correct, and understand why you made each change.</p><p>If you present all of your changes as a single patch (or commit), they |
| may find that it is too much to digest all at once.</p><p>If you present them with the entire history of your work, complete with |
| mistakes, corrections, and dead ends, they may be overwhelmed.</p><p>So the ideal is usually to produce a series of patches such that:</p><div class="orderedlist"><ol type="1"><li> |
| Each patch can be applied in order. |
| </li><li> |
| Each patch includes a single logical change, together with a |
| message explaining the change. |
| </li><li> |
| No patch introduces a regression: after applying any initial |
| part of the series, the resulting project still compiles and |
| works, and has no bugs that it didn't have before. |
| </li><li> |
| The complete series produces the same end result as your own |
| (probably much messier!) development process did. |
| </li></ol></div><p>We will introduce some tools that can help you do this, explain how to |
| use them, and then explain some of the problems that can arise because |
| you are rewriting history.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276686"></a>Keeping a patch series up to date using git-rebase</h2></div></div></div><p>Suppose that you create a branch "mywork" on a remote-tracking branch |
| "origin", and create some commits on top of it:</p><div class="literallayout"><p>$ git checkout -b mywork origin<br> |
| $ vi file.txt<br> |
| $ git commit<br> |
| $ vi otherfile.txt<br> |
| $ git commit<br> |
| ...</p></div><p>You have performed no merges into mywork, so it is just a simple linear |
| sequence of patches on top of "origin":</p><pre class="literallayout">o--o--o <-- origin |
| o--o--o <-- mywork</pre><p>Some more interesting work has been done in the upstream project, and |
| "origin" has advanced:</p><pre class="literallayout">o--o--O--o--o--o <-- origin |
| a--b--c <-- mywork</pre><p>At this point, you could use "pull" to merge your changes back in; |
| the result would create a new merge commit, like this:</p><pre class="literallayout">o--o--O--o--o--o <-- origin |
| \ a--b--c--m <-- mywork</pre><p>However, if you prefer to keep the history in mywork a simple series of |
| commits without any merges, you may instead choose to use |
| <a href="git-rebase.html" target="_top">git-rebase(1)</a>:</p><div class="literallayout"><p>$ git checkout mywork<br> |
| $ git rebase origin</p></div><p>This will remove each of your commits from mywork, temporarily saving |
| them as patches (in a directory named ".dotest"), update mywork to |
| point at the latest version of origin, then apply each of the saved |
| patches to the new mywork. The result will look like:</p><pre class="literallayout">o--o--O--o--o--o <-- origin |
| a'--b'--c' <-- mywork</pre><p>In the process, it may discover conflicts. In that case it will stop |
| and allow you to fix the conflicts; after fixing conflicts, use "git |
| add" to update the index with those contents, and then, instead of |
| running git-commit, just run</p><div class="literallayout"><p>$ git rebase --continue</p></div><p>and git will continue applying the rest of the patches.</p><p>At any point you may use the —abort option to abort this process and |
| return mywork to the state it had before you started the rebase:</p><div class="literallayout"><p>$ git rebase --abort</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276817"></a>Reordering or selecting from a patch series</h2></div></div></div><p>Given one existing commit, the <a href="git-cherry-pick.html" target="_top">git-cherry-pick(1)</a> command |
| allows you to apply the change introduced by that commit and create a |
| new commit that records it. So, for example, if "mywork" points to a |
| series of patches on top of "origin", you might do something like:</p><div class="literallayout"><p>$ git checkout -b mywork-new origin<br> |
| $ gitk origin..mywork &</p></div><p>And browse through the list of patches in the mywork branch using gitk, |
| applying them (possibly in a different order) to mywork-new using |
| cherry-pick, and possibly modifying them as you go using commit |
| —amend.</p><p>Another technique is to use git-format-patch to create a series of |
| patches, then reset the state to before the patches:</p><div class="literallayout"><p>$ git format-patch origin<br> |
| $ git reset --hard origin</p></div><p>Then modify, reorder, or eliminate patches as preferred before applying |
| them again with <a href="git-am.html" target="_top">git-am(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276878"></a>Other tools</h2></div></div></div><p>There are numerous other tools, such as stgit, which exist for the |
| purpose of maintaining a patch series. These are outside of the scope of |
| this manual.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276891"></a>Problems with rewriting history</h2></div></div></div><p>The primary problem with rewriting the history of a branch has to do |
| with merging. Suppose somebody fetches your branch and merges it into |
| their branch, with a result something like this:</p><pre class="literallayout">o--o--O--o--o--o <-- origin |
| \ t--t--t--m <-- their branch:</pre><p>Then suppose you modify the last three commits:</p><pre class="literallayout"> o--o--o <-- new head of origin |
| / |
| o--o--O--o--o--o <-- old head of origin</pre><p>If we examined all this history together in one repository, it will |
| look like:</p><pre class="literallayout"> o--o--o <-- new head of origin |
| / |
| o--o--O--o--o--o <-- old head of origin |
| \ t--t--t--m <-- their branch:</pre><p>Git has no way of knowing that the new head is an updated version of |
| the old head; it treats this situation exactly the same as it would if |
| two developers had independently done the work on the old and new heads |
| in parallel. At this point, if someone attempts to merge the new head |
| in to their branch, git will attempt to merge together the two (old and |
| new) lines of development, instead of trying to replace the old by the |
| new. The results are likely to be unexpected.</p><p>You may still choose to publish branches whose history is rewritten, |
| and it may be useful for others to be able to fetch those branches in |
| order to examine or test them, but they should not attempt to pull such |
| branches into their own work.</p><p>For true distributed development that supports proper merging, |
| published branches should never be rewritten.</p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id276962"></a>Chapter 7. Advanced branch management</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id276968">Fetching individual branches</a></span></dt><dt><span class="section"><a href="#fast-forwards">Understanding git history: fast-forwards</a></span></dt><dt><span class="section"><a href="#id277088">Forcing git fetch to do non-fast-forward updates</a></span></dt><dt><span class="section"><a href="#id277115">Configuring remote branches</a></span></dt></dl></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id276968"></a>Fetching individual branches</h2></div></div></div><p>Instead of using <a href="git-remote.html" target="_top">git-remote(1)</a>, you can also choose just |
| to update one branch at a time, and to store it locally under an |
| arbitrary name:</p><div class="literallayout"><p>$ git fetch origin todo:my-todo-work</p></div><p>The first argument, "origin", just tells git to fetch from the |
| repository you originally cloned from. The second argument tells git |
| to fetch the branch named "todo" from the remote repository, and to |
| store it locally under the name refs/heads/my-todo-work.</p><p>You can also fetch branches from other repositories; so</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git master:example-master</p></div><p>will create a new branch named "example-master" and store in it the |
| branch named "master" from the repository at the given URL. If you |
| already have a branch named example-master, it will attempt to |
| "fast-forward" to the commit given by example.com's master branch. So |
| next we explain what a fast-forward is:</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fast-forwards"></a>Understanding git history: fast-forwards</h2></div></div></div><p>In the previous example, when updating an existing branch, "git |
| fetch" checks to make sure that the most recent commit on the remote |
| branch is a descendant of the most recent commit on your copy of the |
| branch before updating your copy of the branch to point at the new |
| commit. Git calls this process a "fast forward".</p><p>A fast forward looks something like this:</p><pre class="literallayout">o--o--o--o <-- old head of the branch |
| o--o--o <-- new head of the branch</pre><p>In some cases it is possible that the new head will <span class="strong"><strong>not</strong></span> actually be |
| a descendant of the old head. For example, the developer may have |
| realized she made a serious mistake, and decided to backtrack, |
| resulting in a situation like:</p><pre class="literallayout">o--o--o--o--a--b <-- old head of the branch |
| o--o--o <-- new head of the branch</pre><p>In this case, "git fetch" will fail, and print out a warning.</p><p>In that case, you can still force git to update to the new head, as |
| described in the following section. However, note that in the |
| situation above this may mean losing the commits labeled "a" and "b", |
| unless you've already created a reference of your own pointing to |
| them.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277088"></a>Forcing git fetch to do non-fast-forward updates</h2></div></div></div><p>If git fetch fails because the new head of a branch is not a |
| descendant of the old head, you may force the update with:</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git +master:refs/remotes/example/master</p></div><p>Note the addition of the "+" sign. Be aware that commits that the |
| old version of example/master pointed at may be lost, as we saw in |
| the previous section.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277115"></a>Configuring remote branches</h2></div></div></div><p>We saw above that "origin" is just a shortcut to refer to the |
| repository that you originally cloned from. This information is |
| stored in git configuration variables, which you can see using |
| <a href="git-config.html" target="_top">git-config(1)</a>:</p><div class="literallayout"><p>$ git config -l<br> |
| core.repositoryformatversion=0<br> |
| core.filemode=true<br> |
| core.logallrefupdates=true<br> |
| remote.origin.url=git://git.kernel.org/pub/scm/git/git.git<br> |
| remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*<br> |
| branch.master.remote=origin<br> |
| branch.master.merge=refs/heads/master</p></div><p>If there are other repositories that you also use frequently, you can |
| create similar configuration options to save typing; for example, |
| after</p><div class="literallayout"><p>$ git config remote.example.url git://example.com/proj.git</p></div><p>then the following two commands will do the same thing:</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git master:refs/remotes/example/master<br> |
| $ git fetch example master:refs/remotes/example/master</p></div><p>Even better, if you add one more option:</p><div class="literallayout"><p>$ git config remote.example.fetch master:refs/remotes/example/master</p></div><p>then the following commands will all do the same thing:</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git master:ref/remotes/example/master<br> |
| $ git fetch example master:ref/remotes/example/master<br> |
| $ git fetch example example/master<br> |
| $ git fetch example</p></div><p>You can also add a "+" to force the update each time:</p><div class="literallayout"><p>$ git config remote.example.fetch +master:ref/remotes/example/master</p></div><p>Don't do this unless you're sure you won't mind "git fetch" possibly |
| throwing away commits on mybranch.</p><p>Also note that all of the above configuration can be performed by |
| directly editing the file .git/config instead of using |
| <a href="git-config.html" target="_top">git-config(1)</a>.</p><p>See <a href="git-config.html" target="_top">git-config(1)</a> for more details on the configuration |
| options mentioned above.</p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id277239"></a>Chapter 8. Git internals</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id277250">The Object Database</a></span></dt><dt><span class="section"><a href="#id277365">Blob Object</a></span></dt><dt><span class="section"><a href="#id277409">Tree Object</a></span></dt><dt><span class="section"><a href="#id277486">Commit Object</a></span></dt><dt><span class="section"><a href="#id277533">Trust</a></span></dt><dt><span class="section"><a href="#id277583">Tag Object</a></span></dt><dt><span class="section"><a href="#id277630">The "index" aka "Current Directory Cache"</a></span></dt><dt><span class="section"><a href="#id277705">The Workflow</a></span></dt><dd><dl><dt><span class="section"><a href="#id277724">working directory -> index</a></span></dt><dt><span class="section"><a href="#id277813">index -> object database</a></span></dt><dt><span class="section"><a href="#id277841">object database -> index</a></span></dt><dt><span class="section"><a href="#id277872">index -> working directory</a></span></dt><dt><span class="section"><a href="#id277936">Tying it all together</a></span></dt></dl></dd><dt><span class="section"><a href="#id278030">Examining the data</a></span></dt><dt><span class="section"><a href="#id278108">Merging multiple trees</a></span></dt><dt><span class="section"><a href="#id278195">Merging multiple trees, continued</a></span></dt><dt><span class="section"><a href="#id278455">How git stores objects efficiently: pack files</a></span></dt><dt><span class="section"><a href="#dangling-objects">Dangling objects</a></span></dt></dl></div><p>There are two object abstractions: the "object database", and the |
| "current directory cache" aka "index".</p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277250"></a>The Object Database</h2></div></div></div><p>The object database is literally just a content-addressable collection |
| of objects. All objects are named by their content, which is |
| approximated by the SHA1 hash of the object itself. Objects may refer |
| to other objects (by referencing their SHA1 hash), and so you can |
| build up a hierarchy of objects.</p><p>All objects have a statically determined "type" aka "tag", which is |
| determined at object creation time, and which identifies the format of |
| the object (i.e. how it is used, and how it can refer to other |
| objects). There are currently four different object types: "blob", |
| "tree", "commit" and "tag".</p><p>A "blob" object cannot refer to any other object, and is, like the type |
| implies, a pure storage object containing some user data. It is used to |
| actually store the file data, i.e. a blob object is associated with some |
| particular version of some file.</p><p>A "tree" object is an object that ties one or more "blob" objects into a |
| directory structure. In addition, a tree object can refer to other tree |
| objects, thus creating a directory hierarchy.</p><p>A "commit" object ties such directory hierarchies together into |
| a DAG of revisions - each "commit" is associated with exactly one tree |
| (the directory hierarchy at the time of the commit). In addition, a |
| "commit" refers to one or more "parent" commit objects that describe the |
| history of how we arrived at that directory hierarchy.</p><p>As a special case, a commit object with no parents is called the "root" |
| object, and is the point of an initial project commit. Each project |
| must have at least one root, and while you can tie several different |
| root objects together into one project by creating a commit object which |
| has two or more separate roots as its ultimate parents, that's probably |
| just going to confuse people. So aim for the notion of "one root object |
| per project", even if git itself does not enforce that.</p><p>A "tag" object symbolically identifies and can be used to sign other |
| objects. It contains the identifier and type of another object, a |
| symbolic name (of course!) and, optionally, a signature.</p><p>Regardless of object type, all objects share the following |
| characteristics: they are all deflated with zlib, and have a header |
| that not only specifies their type, but also provides size information |
| about the data in the object. It's worth noting that the SHA1 hash |
| that is used to name the object is the hash of the original data |
| plus this header, so <code class="literal">sha1sum</code> <span class="emphasis"><em>file</em></span> does not match the object name |
| for <span class="emphasis"><em>file</em></span>. |
| (Historical note: in the dawn of the age of git the hash |
| was the sha1 of the <span class="emphasis"><em>compressed</em></span> object.)</p><p>As a result, the general consistency of an object can always be tested |
| independently of the contents or the type of the object: all objects can |
| be validated by verifying that (a) their hashes match the content of the |
| file and (b) the object successfully inflates to a stream of bytes that |
| forms a sequence of <ascii type without space> + <space> + <ascii decimal |
| size> + <byte\0> + <binary object data>.</p><p>The structured objects can further have their structure and |
| connectivity to other objects verified. This is generally done with |
| the <code class="literal">git-fsck</code> program, which generates a full dependency graph |
| of all objects, and verifies their internal consistency (in addition |
| to just verifying their superficial consistency through the hash).</p><p>The object types in some more detail:</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277365"></a>Blob Object</h2></div></div></div><p>A "blob" object is nothing but a binary blob of data, and doesn't |
| refer to anything else. There is no signature or any other |
| verification of the data, so while the object is consistent (it <span class="emphasis"><em>is</em></span> |
| indexed by its sha1 hash, so the data itself is certainly correct), it |
| has absolutely no other attributes. No name associations, no |
| permissions. It is purely a blob of data (i.e. normally "file |
| contents").</p><p>In particular, since the blob is entirely defined by its data, if two |
| files in a directory tree (or in multiple different versions of the |
| repository) have the same contents, they will share the same blob |
| object. The object is totally independent of its location in the |
| directory tree, and renaming a file does not change the object that |
| file is associated with in any way.</p><p>A blob is typically created when <a href="git-update-index.html" target="_top">git-update-index(1)</a> |
| is run, and its data can be accessed by <a href="git-cat-file.html" target="_top">git-cat-file(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277409"></a>Tree Object</h2></div></div></div><p>The next hierarchical object type is the "tree" object. A tree object |
| is a list of mode/name/blob data, sorted by name. Alternatively, the |
| mode data may specify a directory mode, in which case instead of |
| naming a blob, that name is associated with another TREE object.</p><p>Like the "blob" object, a tree object is uniquely determined by the |
| set contents, and so two separate but identical trees will always |
| share the exact same object. This is true at all levels, i.e. it's |
| true for a "leaf" tree (which does not refer to any other trees, only |
| blobs) as well as for a whole subdirectory.</p><p>For that reason a "tree" object is just a pure data abstraction: it |
| has no history, no signatures, no verification of validity, except |
| that since the contents are again protected by the hash itself, we can |
| trust that the tree is immutable and its contents never change.</p><p>So you can trust the contents of a tree to be valid, the same way you |
| can trust the contents of a blob, but you don't know where those |
| contents <span class="emphasis"><em>came</em></span> from.</p><p>Side note on trees: since a "tree" object is a sorted list of |
| "filename+content", you can create a diff between two trees without |
| actually having to unpack two trees. Just ignore all common parts, |
| and your diff will look right. In other words, you can effectively |
| (and efficiently) tell the difference between any two random trees by |
| O(n) where "n" is the size of the difference, rather than the size of |
| the tree.</p><p>Side note 2 on trees: since the name of a "blob" depends entirely and |
| exclusively on its contents (i.e. there are no names or permissions |
| involved), you can see trivial renames or permission changes by |
| noticing that the blob stayed the same. However, renames with data |
| changes need a smarter "diff" implementation.</p><p>A tree is created with <a href="git-write-tree.html" target="_top">git-write-tree(1)</a> and |
| its data can be accessed by <a href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>. |
| Two trees can be compared with <a href="git-diff-tree.html" target="_top">git-diff-tree(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277486"></a>Commit Object</h2></div></div></div><p>The "commit" object is an object that introduces the notion of |
| history into the picture. In contrast to the other objects, it |
| doesn't just describe the physical state of a tree, it describes how |
| we got there, and why.</p><p>A "commit" is defined by the tree-object that it results in, the |
| parent commits (zero, one or more) that led up to that point, and a |
| comment on what happened. Again, a commit is not trusted per se: |
| the contents are well-defined and "safe" due to the cryptographically |
| strong signatures at all levels, but there is no reason to believe |
| that the tree is "good" or that the merge information makes sense. |
| The parents do not have to actually have any relationship with the |
| result, for example.</p><p>Note on commits: unlike real SCM's, commits do not contain |
| rename information or file mode change information. All of that is |
| implicit in the trees involved (the result tree, and the result trees |
| of the parents), and describing that makes no sense in this idiotic |
| file manager.</p><p>A commit is created with <a href="git-commit-tree.html" target="_top">git-commit-tree(1)</a> and |
| its data can be accessed by <a href="git-cat-file.html" target="_top">git-cat-file(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277533"></a>Trust</h2></div></div></div><p>An aside on the notion of "trust". Trust is really outside the scope |
| of "git", but it's worth noting a few things. First off, since |
| everything is hashed with SHA1, you <span class="emphasis"><em>can</em></span> trust that an object is |
| intact and has not been messed with by external sources. So the name |
| of an object uniquely identifies a known state - just not a state that |
| you may want to trust.</p><p>Furthermore, since the SHA1 signature of a commit refers to the |
| SHA1 signatures of the tree it is associated with and the signatures |
| of the parent, a single named commit specifies uniquely a whole set |
| of history, with full contents. You can't later fake any step of the |
| way once you have the name of a commit.</p><p>So to introduce some real trust in the system, the only thing you need |
| to do is to digitally sign just <span class="emphasis"><em>one</em></span> special note, which includes the |
| name of a top-level commit. Your digital signature shows others |
| that you trust that commit, and the immutability of the history of |
| commits tells others that they can trust the whole history.</p><p>In other words, you can easily validate a whole archive by just |
| sending out a single email that tells the people the name (SHA1 hash) |
| of the top commit, and digitally sign that email using something |
| like GPG/PGP.</p><p>To assist in this, git also provides the tag object…</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277583"></a>Tag Object</h2></div></div></div><p>Git provides the "tag" object to simplify creating, managing and |
| exchanging symbolic and signed tokens. The "tag" object at its |
| simplest simply symbolically identifies another object by containing |
| the sha1, type and symbolic name.</p><p>However it can optionally contain additional signature information |
| (which git doesn't care about as long as there's less than 8k of |
| it). This can then be verified externally to git.</p><p>Note that despite the tag features, "git" itself only handles content |
| integrity; the trust framework (and signature provision and |
| verification) has to come from outside.</p><p>A tag is created with <a href="git-mktag.html" target="_top">git-mktag(1)</a>, |
| its data can be accessed by <a href="git-cat-file.html" target="_top">git-cat-file(1)</a>, |
| and the signature can be verified by |
| <a href="git-verify-tag.html" target="_top">git-verify-tag(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277630"></a>The "index" aka "Current Directory Cache"</h2></div></div></div><p>The index is a simple binary file, which contains an efficient |
| representation of a virtual directory content at some random time. It |
| does so by a simple array that associates a set of names, dates, |
| permissions and content (aka "blob") objects together. The cache is |
| always kept ordered by name, and names are unique (with a few very |
| specific rules) at any point in time, but the cache has no long-term |
| meaning, and can be partially updated at any time.</p><p>In particular, the index certainly does not need to be consistent with |
| the current directory contents (in fact, most operations will depend on |
| different ways to make the index <span class="emphasis"><em>not</em></span> be consistent with the directory |
| hierarchy), but it has three very important attributes:</p><p><span class="emphasis"><em>(a) it can re-generate the full state it caches (not just the |
| directory structure: it contains pointers to the "blob" objects so |
| that it can regenerate the data too)</em></span></p><p>As a special case, there is a clear and unambiguous one-way mapping |
| from a current directory cache to a "tree object", which can be |
| efficiently created from just the current directory cache without |
| actually looking at any other data. So a directory cache at any one |
| time uniquely specifies one and only one "tree" object (but has |
| additional data to make it easy to match up that tree object with what |
| has happened in the directory)</p><p><span class="emphasis"><em>(b) it has efficient methods for finding inconsistencies between that |
| cached state ("tree object waiting to be instantiated") and the |
| current state.</em></span></p><p><span class="emphasis"><em>(c) it can additionally efficiently represent information about merge |
| conflicts between different tree objects, allowing each pathname to be |
| associated with sufficient information about the trees involved that |
| you can create a three-way merge between them.</em></span></p><p>Those are the ONLY three things that the directory cache does. It's a |
| cache, and the normal operation is to re-generate it completely from a |
| known tree object, or update/compare it with a live tree that is being |
| developed. If you blow the directory cache away entirely, you generally |
| haven't lost any information as long as you have the name of the tree |
| that it described.</p><p>At the same time, the index is at the same time also the |
| staging area for creating new trees, and creating a new tree always |
| involves a controlled modification of the index file. In particular, |
| the index file can have the representation of an intermediate tree that |
| has not yet been instantiated. So the index can be thought of as a |
| write-back cache, which can contain dirty information that has not yet |
| been written back to the backing store.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id277705"></a>The Workflow</h2></div></div></div><p>Generally, all "git" operations work on the index file. Some operations |
| work <span class="strong"><strong>purely</strong></span> on the index file (showing the current state of the |
| index), but most operations move data to and from the index file. Either |
| from the database or from the working directory. Thus there are four |
| main combinations:</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id277724"></a>working directory -> index</h3></div></div></div><p>You update the index with information from the working directory with |
| the <a href="git-update-index.html" target="_top">git-update-index(1)</a> command. You |
| generally update the index information by just specifying the filename |
| you want to update, like so:</p><div class="literallayout"><p>$ git-update-index filename</p></div><p>but to avoid common mistakes with filename globbing etc, the command |
| will not normally add totally new entries or remove old entries, |
| i.e. it will normally just update existing cache entries.</p><p>To tell git that yes, you really do realize that certain files no |
| longer exist, or that new files should be added, you |
| should use the <code class="literal">—remove</code> and <code class="literal">—add</code> flags respectively.</p><p>NOTE! A <code class="literal">—remove</code> flag does <span class="emphasis"><em>not</em></span> mean that subsequent filenames will |
| necessarily be removed: if the files still exist in your directory |
| structure, the index will be updated with their new status, not |
| removed. The only thing <code class="literal">—remove</code> means is that update-cache will be |
| considering a removed file to be a valid thing, and if the file really |
| does not exist any more, it will update the index accordingly.</p><p>As a special case, you can also do <code class="literal">git-update-index —refresh</code>, which |
| will refresh the "stat" information of each index to match the current |
| stat information. It will <span class="emphasis"><em>not</em></span> update the object status itself, and |
| it will only update the fields that are used to quickly test whether |
| an object still matches its old backing store object.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id277813"></a>index -> object database</h3></div></div></div><p>You write your current index file to a "tree" object with the program</p><div class="literallayout"><p>$ git-write-tree</p></div><p>that doesn't come with any options - it will just write out the |
| current index into the set of tree objects that describe that state, |
| and it will return the name of the resulting top-level tree. You can |
| use that tree to re-generate the index at any time by going in the |
| other direction:</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id277841"></a>object database -> index</h3></div></div></div><p>You read a "tree" file from the object database, and use that to |
| populate (and overwrite - don't do this if your index contains any |
| unsaved state that you might want to restore later!) your current |
| index. Normal operation is just</p><div class="literallayout"><p>$ git-read-tree <sha1 of tree></p></div><p>and your index file will now be equivalent to the tree that you saved |
| earlier. However, that is only your <span class="emphasis"><em>index</em></span> file: your working |
| directory contents have not been modified.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id277872"></a>index -> working directory</h3></div></div></div><p>You update your working directory from the index by "checking out" |
| files. This is not a very common operation, since normally you'd just |
| keep your files updated, and rather than write to your working |
| directory, you'd tell the index files about the changes in your |
| working directory (i.e. <code class="literal">git-update-index</code>).</p><p>However, if you decide to jump to a new version, or check out somebody |
| else's version, or just restore a previous tree, you'd populate your |
| index file with read-tree, and then you need to check out the result |
| with</p><div class="literallayout"><p>$ git-checkout-index filename</p></div><p>or, if you want to check out all of the index, use <code class="literal">-a</code>.</p><p>NOTE! git-checkout-index normally refuses to overwrite old files, so |
| if you have an old version of the tree already checked out, you will |
| need to use the "-f" flag (<span class="emphasis"><em>before</em></span> the "-a" flag or the filename) to |
| <span class="emphasis"><em>force</em></span> the checkout.</p><p>Finally, there are a few odds and ends which are not purely moving |
| from one representation to the other:</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id277936"></a>Tying it all together</h3></div></div></div><p>To commit a tree you have instantiated with "git-write-tree", you'd |
| create a "commit" object that refers to that tree and the history |
| behind it - most notably the "parent" commits that preceded it in |
| history.</p><p>Normally a "commit" has one parent: the previous state of the tree |
| before a certain change was made. However, sometimes it can have two |
| or more parent commits, in which case we call it a "merge", due to the |
| fact that such a commit brings together ("merges") two or more |
| previous states represented by other commits.</p><p>In other words, while a "tree" represents a particular directory state |
| of a working directory, a "commit" represents that state in "time", |
| and explains how we got there.</p><p>You create a commit object by giving it the tree that describes the |
| state at the time of the commit, and a list of parents:</p><div class="literallayout"><p>$ git-commit-tree <tree> -p <parent> [-p <parent2> ..]</p></div><p>and then giving the reason for the commit on stdin (either through |
| redirection from a pipe or file, or by just typing it at the tty).</p><p>git-commit-tree will return the name of the object that represents |
| that commit, and you should save it away for later use. Normally, |
| you'd commit a new <code class="literal">HEAD</code> state, and while git doesn't care where you |
| save the note about that state, in practice we tend to just write the |
| result to the file pointed at by <code class="literal">.git/HEAD</code>, so that we can always see |
| what the last committed state was.</p><p>Here is an ASCII art by Jon Loeliger that illustrates how |
| various pieces fit together.</p><div class="literallayout"><p><br> |
| commit-tree<br> |
| commit obj<br> |
| +----+<br> |
| | |<br> |
| | |<br> |
| V V<br> |
| +-----------+<br> |
| | Object DB |<br> |
| | Backing |<br> |
| | Store |<br> |
| +-----------+<br> |
| ^<br> |
| write-tree | |<br> |
| tree obj | |<br> |
| | | read-tree<br> |
| | | tree obj<br> |
| V<br> |
| +-----------+<br> |
| | Index |<br> |
| | "cache" |<br> |
| +-----------+<br> |
| update-index ^<br> |
| blob obj | |<br> |
| | |<br> |
| checkout-index -u | | checkout-index<br> |
| stat | | blob obj<br> |
| V<br> |
| +-----------+<br> |
| | Working |<br> |
| | Directory |<br> |
| +-----------+<br> |
| </p></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id278030"></a>Examining the data</h2></div></div></div><p>You can examine the data represented in the object database and the |
| index with various helper tools. For every object, you can use |
| <a href="git-cat-file.html" target="_top">git-cat-file(1)</a> to examine details about the |
| object:</p><div class="literallayout"><p>$ git-cat-file -t <objectname></p></div><p>shows the type of the object, and once you have the type (which is |
| usually implicit in where you find the object), you can use</p><div class="literallayout"><p>$ git-cat-file blob|tree|commit|tag <objectname></p></div><p>to show its contents. NOTE! Trees have binary content, and as a result |
| there is a special helper for showing that content, called |
| <code class="literal">git-ls-tree</code>, which turns the binary content into a more easily |
| readable form.</p><p>It's especially instructive to look at "commit" objects, since those |
| tend to be small and fairly self-explanatory. In particular, if you |
| follow the convention of having the top commit name in <code class="literal">.git/HEAD</code>, |
| you can do</p><div class="literallayout"><p>$ git-cat-file commit HEAD</p></div><p>to see what the top commit was.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id278108"></a>Merging multiple trees</h2></div></div></div><p>Git helps you do a three-way merge, which you can expand to n-way by |
| repeating the merge procedure arbitrary times until you finally |
| "commit" the state. The normal situation is that you'd only do one |
| three-way merge (two parents), and commit it, but if you like to, you |
| can do multiple parents in one go.</p><p>To do a three-way merge, you need the two sets of "commit" objects |
| that you want to merge, use those to find the closest common parent (a |
| third "commit" object), and then use those commit objects to find the |
| state of the directory ("tree" object) at these points.</p><p>To get the "base" for the merge, you first look up the common parent |
| of two commits with</p><div class="literallayout"><p>$ git-merge-base <commit1> <commit2></p></div><p>which will return you the commit they are both based on. You should |
| now look up the "tree" objects of those commits, which you can easily |
| do with (for example)</p><div class="literallayout"><p>$ git-cat-file commit <commitname> | head -1</p></div><p>since the tree object information is always the first line in a commit |
| object.</p><p>Once you know the three trees you are going to merge (the one "original" |
| tree, aka the common case, and the two "result" trees, aka the branches |
| you want to merge), you do a "merge" read into the index. This will |
| complain if it has to throw away your old index contents, so you should |
| make sure that you've committed those - in fact you would normally |
| always do a merge against your last commit (which should thus match what |
| you have in your current index anyway).</p><p>To do the merge, do</p><div class="literallayout"><p>$ git-read-tree -m -u <origtree> <yourtree> <targettree></p></div><p>which will do all trivial merge operations for you directly in the |
| index file, and you can just write the result out with |
| <code class="literal">git-write-tree</code>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id278195"></a>Merging multiple trees, continued</h2></div></div></div><p>Sadly, many merges aren't trivial. If there are files that have |
| been added.moved or removed, or if both branches have modified the |
| same file, you will be left with an index tree that contains "merge |
| entries" in it. Such an index tree can <span class="emphasis"><em>NOT</em></span> be written out to a tree |
| object, and you will have to resolve any such merge clashes using |
| other tools before you can write out the result.</p><p>You can examine such index state with <code class="literal">git-ls-files —unmerged</code> |
| command. An example:</p><div class="literallayout"><p>$ git-read-tree -m $orig HEAD $target<br> |
| $ git-ls-files --unmerged<br> |
| 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c<br> |
| 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c<br> |
| 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c</p></div><p>Each line of the <code class="literal">git-ls-files —unmerged</code> output begins with |
| the blob mode bits, blob SHA1, <span class="emphasis"><em>stage number</em></span>, and the |
| filename. The <span class="emphasis"><em>stage number</em></span> is git's way to say which tree it |
| came from: stage 1 corresponds to <code class="literal">$orig</code> tree, stage 2 <code class="literal">HEAD</code> |
| tree, and stage3 <code class="literal">$target</code> tree.</p><p>Earlier we said that trivial merges are done inside |
| <code class="literal">git-read-tree -m</code>. For example, if the file did not change |
| from <code class="literal">$orig</code> to <code class="literal">HEAD</code> nor <code class="literal">$target</code>, or if the file changed |
| from <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> the same way, |
| obviously the final outcome is what is in <code class="literal">HEAD</code>. What the |
| above example shows is that file <code class="literal">hello.c</code> was changed from |
| <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> in a different way. |
| You could resolve this by running your favorite 3-way merge |
| program, e.g. <code class="literal">diff3</code> or <code class="literal">merge</code>, on the blob objects from |
| these three stages yourself, like this:</p><div class="literallayout"><p>$ git-cat-file blob 263414f... >hello.c~1<br> |
| $ git-cat-file blob 06fa6a2... >hello.c~2<br> |
| $ git-cat-file blob cc44c73... >hello.c~3<br> |
| $ merge hello.c~2 hello.c~1 hello.c~3</p></div><p>This would leave the merge result in <code class="literal">hello.c~2</code> file, along |
| with conflict markers if there are conflicts. After verifying |
| the merge result makes sense, you can tell git what the final |
| merge result for this file is by:</p><div class="literallayout"><p>$ mv -f hello.c~2 hello.c<br> |
| $ git-update-index hello.c</p></div><p>When a path is in unmerged state, running <code class="literal">git-update-index</code> for |
| that path tells git to mark the path resolved.</p><p>The above is the description of a git merge at the lowest level, |
| to help you understand what conceptually happens under the hood. |
| In practice, nobody, not even git itself, uses three <code class="literal">git-cat-file</code> |
| for this. There is <code class="literal">git-merge-index</code> program that extracts the |
| stages to temporary files and calls a "merge" script on it:</p><div class="literallayout"><p>$ git-merge-index git-merge-one-file hello.c</p></div><p>and that is what higher level <code class="literal">git merge -s resolve</code> is implemented with.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id278455"></a>How git stores objects efficiently: pack files</h2></div></div></div><p>We've seen how git stores each object in a file named after the |
| object's SHA1 hash.</p><p>Unfortunately this system becomes inefficient once a project has a |
| lot of objects. Try this on an old project:</p><div class="literallayout"><p>$ git count-objects<br> |
| 6930 objects, 47620 kilobytes</p></div><p>The first number is the number of objects which are kept in |
| individual files. The second is the amount of space taken up by |
| those "loose" objects.</p><p>You can save space and make git faster by moving these loose objects in |
| to a "pack file", which stores a group of objects in an efficient |
| compressed format; the details of how pack files are formatted can be |
| found in <a href="technical/pack-format.txt" target="_top">technical/pack-format.txt</a>.</p><p>To put the loose objects into a pack, just run git repack:</p><div class="literallayout"><p>$ git repack<br> |
| Generating pack...<br> |
| Done counting 6020 objects.<br> |
| Deltifying 6020 objects.<br> |
| 100% (6020/6020) done<br> |
| Writing 6020 objects.<br> |
| 100% (6020/6020) done<br> |
| Total 6020, written 6020 (delta 4070), reused 0 (delta 0)<br> |
| Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.</p></div><p>You can then run</p><div class="literallayout"><p>$ git prune</p></div><p>to remove any of the "loose" objects that are now contained in the |
| pack. This will also remove any unreferenced objects (which may be |
| created when, for example, you use "git reset" to remove a commit). |
| You can verify that the loose objects are gone by looking at the |
| .git/objects directory or by running</p><div class="literallayout"><p>$ git count-objects<br> |
| 0 objects, 0 kilobytes</p></div><p>Although the object files are gone, any commands that refer to those |
| objects will work exactly as they did before.</p><p>The <a href="git-gc.html" target="_top">git-gc(1)</a> command performs packing, pruning, and more for |
| you, so is normally the only high-level command you need.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dangling-objects"></a>Dangling objects</h2></div></div></div><p>The <a href="git-fsck.html" target="_top">git-fsck(1)</a> command will sometimes complain about dangling |
| objects. They are not a problem.</p><p>The most common cause of dangling objects is that you've rebased a |
| branch, or you have pulled from somebody else who rebased a branch—see |
| <a href="#cleaning-up-history" title="Chapter 6. Rewriting history and maintaining patch series">Chapter 6, <i>Rewriting history and maintaining patch series</i></a>. In that case, the old head of the original |
| branch still exists, as does obviously everything it pointed to. The |
| branch pointer itself just doesn't, since you replaced it with another |
| one.</p><p>There are also other situations too that cause dangling objects. For |
| example, a "dangling blob" may arise because you did a "git add" of a |
| file, but then, before you actually committed it and made it part of the |
| bigger picture, you changed something else in that file and committed |
| that <span class="strong"><strong>updated</strong></span> thing - the old state that you added originally ends up |
| not being pointed to by any commit or tree, so it's now a dangling blob |
| object.</p><p>Similarly, when the "recursive" merge strategy runs, and finds that |
| there are criss-cross merges and thus more than one merge base (which is |
| fairly unusual, but it does happen), it will generate one temporary |
| midway tree (or possibly even more, if you had lots of criss-crossing |
| merges and more than two merge bases) as a temporary internal merge |
| base, and again, those are real objects, but the end result will not end |
| up pointing to them, so they end up "dangling" in your repository.</p><p>Generally, dangling objects aren't anything to worry about. They can |
| even be very useful: if you screw something up, the dangling objects can |
| be how you recover your old tree (say, you did a rebase, and realized |
| that you really didn't want to - you can look at what dangling objects |
| you have, and decide to reset your head to some old dangling state).</p><p>For commits, the most useful thing to do with dangling objects tends to |
| be to do a simple</p><div class="literallayout"><p>$ gitk <dangling-commit-sha-goes-here> --not --all</p></div><p>For blobs and trees, you can't do the same, but you can examine them. |
| You can just do</p><div class="literallayout"><p>$ git show <dangling-blob/tree-sha-goes-here></p></div><p>to show what the contents of the blob were (or, for a tree, basically |
| what the "ls" for that directory was), and that may give you some idea |
| of what the operation was that left that dangling object.</p><p>Usually, dangling blobs and trees aren't very interesting. They're |
| almost always the result of either being a half-way mergebase (the blob |
| will often even have the conflict markers from a merge in it, if you |
| have had conflicting merges that you fixed up by hand), or simply |
| because you interrupted a "git fetch" with ^C or something like that, |
| leaving _some_ of the new objects in the object database, but just |
| dangling and useless.</p><p>Anyway, once you are sure that you're not interested in any dangling |
| state, you can just prune all unreachable objects:</p><div class="literallayout"><p>$ git prune</p></div><p>and they'll be gone. But you should only run "git prune" on a quiescent |
| repository - it's kind of like doing a filesystem fsck recovery: you |
| don't want to do that while the filesystem is mounted.</p><p>(The same is true of "git-fsck" itself, btw - but since |
| git-fsck never actually <span class="strong"><strong>changes</strong></span> the repository, it just reports |
| on what it found, git-fsck itself is never "dangerous" to run. |
| Running it while somebody is actually changing the repository can cause |
| confusing and scary messages, but it won't actually do anything bad. In |
| contrast, running "git prune" while somebody is actively changing the |
| repository is a <span class="strong"><strong>BAD</strong></span> idea).</p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id278715"></a>Chapter 9. Glossary of git terms</h2></div></div></div><div class="variablelist"><dl><dt><span class="term"> |
| alternate object database |
| </span></dt><dd> |
| Via the alternates mechanism, a repository can inherit part of its |
| object database from another object database, which is called |
| "alternate". |
| </dd><dt><span class="term"> |
| bare repository |
| </span></dt><dd> |
| A bare repository is normally an appropriately named |
| directory with a <code class="literal">.git</code> suffix that does not have a |
| locally checked-out copy of any of the files under revision |
| control. That is, all of the <code class="literal">git</code> administrative and |
| control files that would normally be present in the |
| hidden <code class="literal">.git</code> sub-directory are directly present in |
| the <code class="literal">repository.git</code> directory instead, and no other files |
| are present and checked out. Usually publishers of public |
| repositories make bare repositories available. |
| </dd><dt><span class="term"> |
| blob object |
| </span></dt><dd> |
| Untyped object, e.g. the contents of a file. |
| </dd><dt><span class="term"> |
| branch |
| </span></dt><dd> |
| A non-cyclical graph of revisions, i.e. the complete history of |
| a particular revision, which is called the branch head. The |
| branch heads are stored in <code class="literal">$GIT_DIR/refs/heads/</code>. |
| </dd><dt><span class="term"> |
| cache |
| </span></dt><dd> |
| Obsolete for: index. |
| </dd><dt><span class="term"> |
| chain |
| </span></dt><dd> |
| A list of objects, where each object in the list contains a |
| reference to its successor (for example, the successor of a commit |
| could be one of its parents). |
| </dd><dt><span class="term"> |
| changeset |
| </span></dt><dd> |
| BitKeeper/cvsps speak for "commit". Since git does not store |
| changes, but states, it really does not make sense to use |
| the term "changesets" with git. |
| </dd><dt><span class="term"> |
| checkout |
| </span></dt><dd> |
| The action of updating the working tree to a revision which was |
| stored in the object database. |
| </dd><dt><span class="term"> |
| cherry-picking |
| </span></dt><dd> |
| In SCM jargon, "cherry pick" means to choose a subset of |
| changes out of a series of changes (typically commits) |
| and record them as a new series of changes on top of |
| different codebase. In GIT, this is performed by |
| "git cherry-pick" command to extract the change |
| introduced by an existing commit and to record it based |
| on the tip of the current branch as a new commit. |
| </dd><dt><span class="term"> |
| clean |
| </span></dt><dd> |
| A working tree is clean, if it corresponds to the revision |
| referenced by the current head. Also see "dirty". |
| </dd><dt><span class="term"> |
| commit |
| </span></dt><dd> |
| As a verb: The action of storing the current state of the index in the |
| object database. The result is a revision. |
| As a noun: Short hand for commit object. |
| </dd><dt><span class="term"> |
| commit object |
| </span></dt><dd> |
| An object which contains the information about a particular |
| revision, such as parents, committer, author, date and the |
| tree object which corresponds to the top directory of the |
| stored revision. |
| </dd><dt><span class="term"> |
| core git |
| </span></dt><dd> |
| Fundamental data structures and utilities of git. Exposes only |
| limited source code management tools. |
| </dd><dt><span class="term"> |
| DAG |
| </span></dt><dd> |
| Directed acyclic graph. The commit objects form a directed acyclic |
| graph, because they have parents (directed), and the graph of commit |
| objects is acyclic (there is no chain which begins and ends with the |
| same object). |
| </dd><dt><span class="term"> |
| dircache |
| </span></dt><dd> |
| You are <span class="strong"><strong>waaaaay</strong></span> behind. |
| </dd><dt><span class="term"> |
| dirty |
| </span></dt><dd> |
| A working tree is said to be dirty if it contains modifications |
| which have not been committed to the current branch. |
| </dd><dt><span class="term"> |
| directory |
| </span></dt><dd> |
| The list you get with "ls" :-) |
| </dd><dt><span class="term"> |
| ent |
| </span></dt><dd> |
| Favorite synonym to "tree-ish" by some total geeks. See |
| <code class="literal">http://en.wikipedia.org/wiki/Ent_(Middle-earth)</code> for an in-depth |
| explanation. Avoid this term, not to confuse people. |
| </dd><dt><span class="term"> |
| fast forward |
| </span></dt><dd> |
| A fast-forward is a special type of merge where you have |
| a revision and you are "merging" another branch's changes |
| that happen to be a descendant of what you have. |
| In such these cases, you do not make a new merge commit but |
| instead just update to his revision. This will happen |
| frequently on a tracking branch of a remote repository. |
| </dd><dt><span class="term"> |
| fetch |
| </span></dt><dd> |
| Fetching a branch means to get the branch's head ref from a |
| remote repository, to find out which objects are missing from |
| the local object database, and to get them, too. |
| </dd><dt><span class="term"> |
| file system |
| </span></dt><dd> |
| Linus Torvalds originally designed git to be a user space file |
| system, i.e. the infrastructure to hold files and directories. |
| That ensured the efficiency and speed of git. |
| </dd><dt><span class="term"> |
| git archive |
| </span></dt><dd> |
| Synonym for repository (for arch people). |
| </dd><dt><span class="term"> |
| grafts |
| </span></dt><dd> |
| Grafts enables two otherwise different lines of development to be |
| joined together by recording fake ancestry information for commits. |
| This way you can make git pretend the set of parents a commit |
| has is different from what was recorded when the commit was created. |
| Configured via the <code class="literal">.git/info/grafts</code> file. |
| </dd><dt><span class="term"> |
| hash |
| </span></dt><dd> |
| In git's context, synonym to object name. |
| </dd><dt><span class="term"> |
| head |
| </span></dt><dd> |
| The top of a branch. It contains a ref to the corresponding |
| commit object. |
| </dd><dt><span class="term"> |
| head ref |
| </span></dt><dd> |
| A ref pointing to a head. Often, this is abbreviated to "head". |
| Head refs are stored in <code class="literal">$GIT_DIR/refs/heads/</code>. |
| </dd><dt><span class="term"> |
| hook |
| </span></dt><dd> |
| During the normal execution of several git commands, |
| call-outs are made to optional scripts that allow |
| a developer to add functionality or checking. |
| Typically, the hooks allow for a command to be pre-verified |
| and potentially aborted, and allow for a post-notification |
| after the operation is done. |
| The hook scripts are found in the <code class="literal">$GIT_DIR/hooks/</code> directory, |
| and are enabled by simply making them executable. |
| </dd><dt><span class="term"> |
| index |
| </span></dt><dd> |
| A collection of files with stat information, whose contents are |
| stored as objects. The index is a stored version of your working |
| tree. Truth be told, it can also contain a second, and even a third |
| version of a working tree, which are used when merging. |
| </dd><dt><span class="term"> |
| index entry |
| </span></dt><dd> |
| The information regarding a particular file, stored in the index. |
| An index entry can be unmerged, if a merge was started, but not |
| yet finished (i.e. if the index contains multiple versions of |
| that file). |
| </dd><dt><span class="term"> |
| master |
| </span></dt><dd> |
| The default development branch. Whenever you create a git |
| repository, a branch named "master" is created, and becomes |
| the active branch. In most cases, this contains the local |
| development, though that is purely conventional and not required. |
| </dd><dt><span class="term"> |
| merge |
| </span></dt><dd> |
| To merge branches means to try to accumulate the changes since a |
| common ancestor and apply them to the first branch. An automatic |
| merge uses heuristics to accomplish that. Evidently, an automatic |
| merge can fail. |
| </dd><dt><span class="term"> |
| object |
| </span></dt><dd> |
| The unit of storage in git. It is uniquely identified by |
| the SHA1 of its contents. Consequently, an object can not |
| be changed. |
| </dd><dt><span class="term"> |
| object database |
| </span></dt><dd> |
| Stores a set of "objects", and an individual object is identified |
| by its object name. The objects usually live in <code class="literal">$GIT_DIR/objects/</code>. |
| </dd><dt><span class="term"> |
| object identifier |
| </span></dt><dd> |
| Synonym for object name. |
| </dd><dt><span class="term"> |
| object name |
| </span></dt><dd> |
| The unique identifier of an object. The hash of the object's contents |
| using the Secure Hash Algorithm 1 and usually represented by the 40 |
| character hexadecimal encoding of the hash of the object (possibly |
| followed by a white space). |
| </dd><dt><span class="term"> |
| object type |
| </span></dt><dd> |
| One of the identifiers "commit","tree","tag" and "blob" describing |
| the type of an object. |
| </dd><dt><span class="term"> |
| octopus |
| </span></dt><dd> |
| To merge more than two branches. Also denotes an intelligent |
| predator. |
| </dd><dt><span class="term"> |
| origin |
| </span></dt><dd> |
| The default upstream repository. Most projects have at |
| least one upstream project which they track. By default |
| <span class="emphasis"><em>origin</em></span> is used for that purpose. New upstream updates |
| will be fetched into remote tracking branches named |
| origin/name-of-upstream-branch, which you can see using |
| "git branch -r". |
| </dd><dt><span class="term"> |
| pack |
| </span></dt><dd> |
| A set of objects which have been compressed into one file (to save |
| space or to transmit them efficiently). |
| </dd><dt><span class="term"> |
| pack index |
| </span></dt><dd> |
| The list of identifiers, and other information, of the objects in a |
| pack, to assist in efficiently accessing the contents of a pack. |
| </dd><dt><span class="term"> |
| parent |
| </span></dt><dd> |
| A commit object contains a (possibly empty) list of the logical |
| predecessor(s) in the line of development, i.e. its parents. |
| </dd><dt><span class="term"> |
| pickaxe |
| </span></dt><dd> |
| The term pickaxe refers to an option to the diffcore routines |
| that help select changes that add or delete a given text string. |
| With the —pickaxe-all option, it can be used to view the |
| full changeset that introduced or removed, say, a particular |
| line of text. See <a href="git-diff.html" target="_top">git-diff(1)</a>. |
| </dd><dt><span class="term"> |
| plumbing |
| </span></dt><dd> |
| Cute name for core git. |
| </dd><dt><span class="term"> |
| porcelain |
| </span></dt><dd> |
| Cute name for programs and program suites depending on core git, |
| presenting a high level access to core git. Porcelains expose |
| more of a SCM interface than the plumbing. |
| </dd><dt><span class="term"> |
| pull |
| </span></dt><dd> |
| Pulling a branch means to fetch it and merge it. |
| </dd><dt><span class="term"> |
| push |
| </span></dt><dd> |
| Pushing a branch means to get the branch's head ref from a remote |
| repository, find out if it is an ancestor to the branch's local |
| head ref is a direct, and in that case, putting all objects, which |
| are reachable from the local head ref, and which are missing from |
| the remote repository, into the remote object database, and updating |
| the remote head ref. If the remote head is not an ancestor to the |
| local head, the push fails. |
| </dd><dt><span class="term"> |
| reachable |
| </span></dt><dd> |
| All of the ancestors of a given commit are said to be reachable from |
| that commit. More generally, one object is reachable from another if |
| we can reach the one from the other by a chain that follows tags to |
| whatever they tag, commits to their parents or trees, and trees to the |
| trees or blobs that they contain. |
| </dd><dt><span class="term"> |
| rebase |
| </span></dt><dd> |
| To clean a branch by starting from the head of the main line of |
| development ("master"), and reapply the (possibly cherry-picked) |
| changes from that branch. |
| </dd><dt><span class="term"> |
| ref |
| </span></dt><dd> |
| A 40-byte hex representation of a SHA1 or a name that denotes |
| a particular object. These may be stored in <code class="literal">$GIT_DIR/refs/</code>. |
| </dd><dt><span class="term"> |
| refspec |
| </span></dt><dd> |
| A refspec is used by fetch and push to describe the mapping |
| between remote ref and local ref. They are combined with |
| a colon in the format <src>:<dst>, preceded by an optional |
| plus sign, +. For example: |
| <code class="literal">git fetch $URL refs/heads/master:refs/heads/origin</code> |
| means "grab the master branch head from the $URL and store |
| it as my origin branch head". |
| And <code class="literal">git push $URL refs/heads/master:refs/heads/to-upstream</code> |
| means "publish my master branch head as to-upstream branch |
| at $URL". See also <a href="git-push.html" target="_top">git-push(1)</a> |
| </dd><dt><span class="term"> |
| repository |
| </span></dt><dd> |
| A collection of refs together with an object database containing |
| all objects, which are reachable from the refs, possibly accompanied |
| by meta data from one or more porcelains. A repository can |
| share an object database with other repositories. |
| </dd><dt><span class="term"> |
| resolve |
| </span></dt><dd> |
| The action of fixing up manually what a failed automatic merge |
| left behind. |
| </dd><dt><span class="term"> |
| revision |
| </span></dt><dd> |
| A particular state of files and directories which was stored in |
| the object database. It is referenced by a commit object. |
| </dd><dt><span class="term"> |
| rewind |
| </span></dt><dd> |
| To throw away part of the development, i.e. to assign the head to |
| an earlier revision. |
| </dd><dt><span class="term"> |
| SCM |
| </span></dt><dd> |
| Source code management (tool). |
| </dd><dt><span class="term"> |
| SHA1 |
| </span></dt><dd> |
| Synonym for object name. |
| </dd><dt><span class="term"> |
| shallow repository |
| </span></dt><dd> |
| A shallow repository has an incomplete history some of |
| whose commits have parents cauterized away (in other |
| words, git is told to pretend that these commits do not |
| have the parents, even though they are recorded in the |
| commit object). This is sometimes useful when you are |
| interested only in the recent history of a project even |
| though the real history recorded in the upstream is |
| much larger. A shallow repository is created by giving |
| <code class="literal">—depth</code> option to <a href="git-clone.html" target="_top">git-clone(1)</a>, and its |
| history can be later deepened with <a href="git-fetch.html" target="_top">git-fetch(1)</a>. |
| </dd><dt><span class="term"> |
| symref |
| </span></dt><dd> |
| Symbolic reference: instead of containing the SHA1 id itself, it |
| is of the format <span class="emphasis"><em>ref: refs/some/thing</em></span> and when referenced, it |
| recursively dereferences to this reference. <span class="emphasis"><em>HEAD</em></span> is a prime |
| example of a symref. Symbolic references are manipulated with |
| the <a href="git-symbolic-ref.html" target="_top">git-symbolic-ref(1)</a> command. |
| </dd><dt><span class="term"> |
| topic branch |
| </span></dt><dd> |
| A regular git branch that is used by a developer to |
| identify a conceptual line of development. Since branches |
| are very easy and inexpensive, it is often desirable to |
| have several small branches that each contain very well |
| defined concepts or small incremental yet related changes. |
| </dd><dt><span class="term"> |
| tracking branch |
| </span></dt><dd> |
| A regular git branch that is used to follow changes from |
| another repository. A tracking branch should not contain |
| direct modifications or have local commits made to it. |
| A tracking branch can usually be identified as the |
| right-hand-side ref in a Pull: refspec. |
| </dd><dt><span class="term"> |
| tree object |
| </span></dt><dd> |
| An object containing a list of file names and modes along with refs |
| to the associated blob and/or tree objects. A tree is equivalent |
| to a directory. |
| </dd><dt><span class="term"> |
| tree |
| </span></dt><dd> |
| Either a working tree, or a tree object together with the |
| dependent blob and tree objects (i.e. a stored representation |
| of a working tree). |
| </dd><dt><span class="term"> |
| tree-ish |
| </span></dt><dd> |
| A ref pointing to either a commit object, a tree object, or a |
| tag object pointing to a tag or commit or tree object. |
| </dd><dt><span class="term"> |
| tag object |
| </span></dt><dd> |
| An object containing a ref pointing to another object, which can |
| contain a message just like a commit object. It can also |
| contain a (PGP) signature, in which case it is called a "signed |
| tag object". |
| </dd><dt><span class="term"> |
| tag |
| </span></dt><dd> |
| A ref pointing to a tag or commit object. In contrast to a head, |
| a tag is not changed by a commit. Tags (not tag objects) are |
| stored in <code class="literal">$GIT_DIR/refs/tags/</code>. A git tag has nothing to do with |
| a Lisp tag (which is called object type in git's context). |
| A tag is most typically used to mark a particular point in the |
| commit ancestry chain. |
| </dd><dt><span class="term"> |
| unmerged index |
| </span></dt><dd> |
| An index which contains unmerged index entries. |
| </dd><dt><span class="term"> |
| working tree |
| </span></dt><dd> |
| The set of files and directories currently being worked on, |
| i.e. you can work in your working tree without using git at all. |
| </dd></dl></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id279930"></a>Chapter 10. Notes and todo list for this manual</h2></div></div></div><p>This is a work in progress.</p><p>The basic requirements: |
| - It must be readable in order, from beginning to end, by |
| someone intelligent with a basic grasp of the unix |
| commandline, but without any special knowledge of git. If |
| necessary, any other prerequisites should be specifically |
| mentioned as they arise. |
| - Whenever possible, section headings should clearly describe |
| the task they explain how to do, in language that requires |
| no more knowledge than necessary: for example, "importing |
| patches into a project" rather than "the git-am command"</p><p>Think about how to create a clear chapter dependency graph that will |
| allow people to get to important topics without necessarily reading |
| everything in between.</p><p>Say something about .gitignore.</p><p>Scan Documentation/ for other stuff left out; in particular: |
| howto's |
| some of technical/? |
| hooks |
| list of commands in <a href="git.html" target="_top">git(1)</a></p><p>Scan email archives for other stuff left out</p><p>Scan man pages to see if any assume more background than this manual |
| provides.</p><p>Simplify beginning by suggesting disconnected head instead of |
| temporary branch creation?</p><p>Explain how to refer to file stages in the "how to resolve a merge" |
| section: diff -1, -2, -3, —ours, —theirs :1:/path notation. The |
| "git ls-files —unmerged —stage" thing is sorta useful too, |
| actually. And note gitk —merge.</p><p>Add more good examples. Entire sections of just cookbook examples |
| might be a good idea; maybe make an "advanced examples" section a |
| standard end-of-chapter section?</p><p>Include cross-references to the glossary, where appropriate.</p><p>Document shallow clones? See draft 1.5.0 release notes for some |
| documentation.</p><p>Add a section on working with other version control systems, including |
| CVS, Subversion, and just imports of series of release tarballs.</p><p>More details on gitweb?</p><p>Write a chapter on using plumbing and writing scripts.</p></div></div></body></html> |
