2962 lines
108 KiB
Plaintext
2962 lines
108 KiB
Plaintext
Git User's Manual
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_________________
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This manual is designed to be readable by someone with basic unix
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commandline skills, but no previous knowledge of git.
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Chapter 1 gives a brief overview of git commands, without any
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explanation; you may prefer to skip to chapter 2 on a first reading.
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Chapters 2 and 3 explain how to fetch and study a project using
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git--the tools you'd need to build and test a particular version of a
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software project, to search for regressions, and so on.
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Chapter 4 explains how to do development with git, and chapter 5 how
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to share that development with others.
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Further chapters cover more specialized topics.
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Comprehensive reference documentation is available through the man
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pages. For a command such as "git clone", just use
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------------------------------------------------
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$ man git-clone
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------------------------------------------------
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Git Quick Start
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===============
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This is a quick summary of the major commands; the following chapters
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will explain how these work in more detail.
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Creating a new repository
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-------------------------
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From a tarball:
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-----------------------------------------------
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$ tar xzf project.tar.gz
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$ cd project
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$ git init
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Initialized empty Git repository in .git/
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$ git add .
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$ git commit
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-----------------------------------------------
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From a remote repository:
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$ git clone git://example.com/pub/project.git
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$ cd project
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-----------------------------------------------
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Managing branches
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-----------------
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-----------------------------------------------
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$ git branch # list all branches in this repo
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$ git checkout test # switch working directory to branch "test"
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$ git branch new # create branch "new" starting at current HEAD
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$ git branch -d new # delete branch "new"
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-----------------------------------------------
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Instead of basing new branch on current HEAD (the default), use:
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-----------------------------------------------
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$ git branch new test # branch named "test"
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$ git branch new v2.6.15 # tag named v2.6.15
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$ git branch new HEAD^ # commit before the most recent
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$ git branch new HEAD^^ # commit before that
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$ git branch new test~10 # ten commits before tip of branch "test"
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-----------------------------------------------
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Create and switch to a new branch at the same time:
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-----------------------------------------------
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$ git checkout -b new v2.6.15
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-----------------------------------------------
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Update and examine branches from the repository you cloned from:
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-----------------------------------------------
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$ git fetch # update
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$ git branch -r # list
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origin/master
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origin/next
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...
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$ git branch checkout -b masterwork origin/master
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-----------------------------------------------
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Fetch a branch from a different repository, and give it a new
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name in your repository:
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-----------------------------------------------
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$ git fetch git://example.com/project.git theirbranch:mybranch
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$ git fetch git://example.com/project.git v2.6.15:mybranch
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-----------------------------------------------
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Keep a list of repositories you work with regularly:
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-----------------------------------------------
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$ git remote add example git://example.com/project.git
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$ git remote # list remote repositories
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example
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origin
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$ git remote show example # get details
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* remote example
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URL: git://example.com/project.git
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Tracked remote branches
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master next ...
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$ git fetch example # update branches from example
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$ git branch -r # list all remote branches
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-----------------------------------------------
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Exploring history
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-----------------
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-----------------------------------------------
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$ gitk # visualize and browse history
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$ git log # list all commits
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$ git log src/ # ...modifying src/
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$ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15
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$ git log master..test # ...in branch test, not in branch master
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$ git log test..master # ...in branch master, but not in test
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$ git log test...master # ...in one branch, not in both
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$ git log -S'foo()' # ...where difference contain "foo()"
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$ git log --since="2 weeks ago"
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$ git log -p # show patches as well
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$ git show # most recent commit
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$ git diff v2.6.15..v2.6.16 # diff between two tagged versions
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$ git diff v2.6.15..HEAD # diff with current head
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$ git grep "foo()" # search working directory for "foo()"
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$ git grep v2.6.15 "foo()" # search old tree for "foo()"
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$ git show v2.6.15:a.txt # look at old version of a.txt
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-----------------------------------------------
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Search for regressions:
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$ git bisect start
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$ git bisect bad # current version is bad
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$ git bisect good v2.6.13-rc2 # last known good revision
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Bisecting: 675 revisions left to test after this
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# test here, then:
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$ git bisect good # if this revision is good, or
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$ git bisect bad # if this revision is bad.
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# repeat until done.
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-----------------------------------------------
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Making changes
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--------------
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Make sure git knows who to blame:
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------------------------------------------------
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$ cat >~/.gitconfig <<\EOF
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[user]
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name = Your Name Comes Here
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email = you@yourdomain.example.com
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EOF
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------------------------------------------------
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Select file contents to include in the next commit, then make the
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commit:
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-----------------------------------------------
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$ git add a.txt # updated file
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$ git add b.txt # new file
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$ git rm c.txt # old file
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$ git commit
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-----------------------------------------------
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Or, prepare and create the commit in one step:
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-----------------------------------------------
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$ git commit d.txt # use latest content only of d.txt
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$ git commit -a # use latest content of all tracked files
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-----------------------------------------------
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Merging
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-------
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-----------------------------------------------
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$ git merge test # merge branch "test" into the current branch
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$ git pull git://example.com/project.git master
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# fetch and merge in remote branch
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$ git pull . test # equivalent to git merge test
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-----------------------------------------------
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Sharing your changes
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--------------------
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Importing or exporting patches:
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-----------------------------------------------
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$ git format-patch origin..HEAD # format a patch for each commit
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# in HEAD but not in origin
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$ git-am mbox # import patches from the mailbox "mbox"
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-----------------------------------------------
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Fetch a branch in a different git repository, then merge into the
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current branch:
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$ git pull git://example.com/project.git theirbranch
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-----------------------------------------------
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Store the fetched branch into a local branch before merging into the
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current branch:
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$ git pull git://example.com/project.git theirbranch:mybranch
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-----------------------------------------------
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After creating commits on a local branch, update the remote
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branch with your commits:
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$ git push ssh://example.com/project.git mybranch:theirbranch
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-----------------------------------------------
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When remote and local branch are both named "test":
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$ git push ssh://example.com/project.git test
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-----------------------------------------------
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Shortcut version for a frequently used remote repository:
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$ git remote add example ssh://example.com/project.git
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$ git push example test
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-----------------------------------------------
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Repository maintenance
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----------------------
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Check for corruption:
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$ git fsck
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-----------------------------------------------
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Recompress, remove unused cruft:
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$ git gc
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-----------------------------------------------
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Repositories and Branches
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=========================
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How to get a git repository
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---------------------------
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It will be useful to have a git repository to experiment with as you
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read this manual.
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The best way to get one is by using the gitlink:git-clone[1] command
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to download a copy of an existing repository for a project that you
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are interested in. If you don't already have a project in mind, here
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are some interesting examples:
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------------------------------------------------
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# git itself (approx. 10MB download):
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$ git clone git://git.kernel.org/pub/scm/git/git.git
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# the linux kernel (approx. 150MB download):
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$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
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------------------------------------------------
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The initial clone may be time-consuming for a large project, but you
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will only need to clone once.
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The clone command creates a new directory named after the project
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("git" or "linux-2.6" in the examples above). After you cd into this
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directory, you will see that it contains a copy of the project files,
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together with a special top-level directory named ".git", which
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contains all the information about the history of the project.
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In most of the following, examples will be taken from one of the two
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repositories above.
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How to check out a different version of a project
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-------------------------------------------------
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Git is best thought of as a tool for storing the history of a
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collection of files. It stores the history as a compressed
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collection of interrelated snapshots (versions) of the project's
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contents.
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A single git repository may contain multiple branches. Each branch
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is a bookmark referencing a particular point in the project history.
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The gitlink:git-branch[1] command shows you the list of branches:
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------------------------------------------------
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$ git branch
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* master
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------------------------------------------------
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A freshly cloned repository contains a single branch, named "master",
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and the working directory contains the version of the project
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referred to by the master branch.
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Most projects also use tags. Tags, like branches, are references
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into the project's history, and can be listed using the
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gitlink:git-tag[1] command:
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------------------------------------------------
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$ git tag -l
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v2.6.11
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v2.6.11-tree
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v2.6.12
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v2.6.12-rc2
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v2.6.12-rc3
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v2.6.12-rc4
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v2.6.12-rc5
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v2.6.12-rc6
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v2.6.13
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...
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------------------------------------------------
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Tags are expected to always point at the same version of a project,
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while branches are expected to advance as development progresses.
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Create a new branch pointing to one of these versions and check it
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out using gitlink:git-checkout[1]:
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------------------------------------------------
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$ git checkout -b new v2.6.13
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------------------------------------------------
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The working directory then reflects the contents that the project had
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when it was tagged v2.6.13, and gitlink:git-branch[1] shows two
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branches, with an asterisk marking the currently checked-out branch:
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------------------------------------------------
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$ git branch
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master
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* new
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------------------------------------------------
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If you decide that you'd rather see version 2.6.17, you can modify
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the current branch to point at v2.6.17 instead, with
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------------------------------------------------
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$ git reset --hard v2.6.17
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------------------------------------------------
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Note that if the current branch was your only reference to a
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particular point in history, then resetting that branch may leave you
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with no way to find the history it used to point to; so use this
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command carefully.
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Understanding History: Commits
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------------------------------
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Every change in the history of a project is represented by a commit.
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The gitlink:git-show[1] command shows the most recent commit on the
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current branch:
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------------------------------------------------
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$ git show
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commit 2b5f6dcce5bf94b9b119e9ed8d537098ec61c3d2
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Author: Jamal Hadi Salim <hadi@cyberus.ca>
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Date: Sat Dec 2 22:22:25 2006 -0800
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[XFRM]: Fix aevent structuring to be more complete.
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aevents can not uniquely identify an SA. We break the ABI with this
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patch, but consensus is that since it is not yet utilized by any
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(known) application then it is fine (better do it now than later).
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Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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diff --git a/Documentation/networking/xfrm_sync.txt b/Documentation/networking/xfrm_sync.txt
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index 8be626f..d7aac9d 100644
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--- a/Documentation/networking/xfrm_sync.txt
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+++ b/Documentation/networking/xfrm_sync.txt
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@@ -47,10 +47,13 @@ aevent_id structure looks like:
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struct xfrm_aevent_id {
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struct xfrm_usersa_id sa_id;
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+ xfrm_address_t saddr;
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__u32 flags;
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+ __u32 reqid;
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};
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...
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------------------------------------------------
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As you can see, a commit shows who made the latest change, what they
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did, and why.
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Every commit has a 40-hexdigit id, sometimes called the "object name"
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or the "SHA1 id", shown on the first line of the "git show" output.
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You can usually refer to a commit by a shorter name, such as a tag or a
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branch name, but this longer name can also be useful. Most
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importantly, it is a globally unique name for this commit: so if you
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tell somebody else the object name (for example in email), then you are
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guaranteed that name will refer to the same commit in their repository
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that it does in yours (assuming their repository has that commit at
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all).
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Understanding history: commits, parents, and reachability
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Every commit (except the very first commit in a project) also has a
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parent commit which shows what happened before this commit.
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Following the chain of parents will eventually take you back to the
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beginning of the project.
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However, the commits do not form a simple list; git allows lines of
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development to diverge and then reconverge, and the point where two
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lines of development reconverge is called a "merge". The commit
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representing a merge can therefore have more than one parent, with
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each parent representing the most recent commit on one of the lines
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of development leading to that point.
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The best way to see how this works is using the gitlink:gitk[1]
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command; running gitk now on a git repository and looking for merge
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commits will help understand how the git organizes history.
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In the following, we say that commit X is "reachable" from commit Y
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if commit X is an ancestor of commit Y. Equivalently, you could say
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that Y is a descendent of X, or that there is a chain of parents
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leading from commit Y to commit X.
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Understanding history: History diagrams
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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We will sometimes represent git history using diagrams like the one
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below. Commits are shown as "o", and the links between them with
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lines drawn with - / and \. Time goes left to right:
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o--o--o <-- Branch A
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/
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o--o--o <-- master
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\
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o--o--o <-- Branch B
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If we need to talk about a particular commit, the character "o" may
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be replaced with another letter or number.
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Understanding history: What is a branch?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Though we've been using the word "branch" to mean a kind of reference
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to a particular commit, the word branch is also commonly used to
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refer to the line of commits leading up to that point. In the
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example above, git may think of the branch named "A" as just a
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pointer to one particular commit, but we may refer informally to the
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line of three commits leading up to that point as all being part of
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"branch A".
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If we need to make it clear that we're just talking about the most
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recent commit on the branch, we may refer to that commit as the
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"head" of the branch.
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Manipulating branches
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---------------------
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Creating, deleting, and modifying branches is quick and easy; here's
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a summary of the commands:
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git branch::
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list all branches
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git branch <branch>::
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create a new branch named <branch>, referencing the same
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point in history as the current branch
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git branch <branch> <start-point>::
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create a new branch named <branch>, referencing
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<start-point>, which may be specified any way you like,
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including using a branch name or a tag name
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git branch -d <branch>::
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delete the branch <branch>; if the branch you are deleting
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points to a commit which is not reachable from this branch,
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this command will fail with a warning.
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git branch -D <branch>::
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even if the branch points to a commit not reachable
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from the current branch, you may know that that commit
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is still reachable from some other branch or tag. In that
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case it is safe to use this command to force git to delete
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the branch.
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git checkout <branch>::
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make the current branch <branch>, updating the working
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directory to reflect the version referenced by <branch>
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git checkout -b <new> <start-point>::
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create a new branch <new> referencing <start-point>, and
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check it out.
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It is also useful to know that the special symbol "HEAD" can always
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be used to refer to the current branch.
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Examining branches from a remote repository
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-------------------------------------------
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The "master" branch that was created at the time you cloned is a copy
|
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of the HEAD in the repository that you cloned from. That repository
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may also have had other branches, though, and your local repository
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keeps branches which track each of those remote branches, which you
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can view using the "-r" option to gitlink:git-branch[1]:
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------------------------------------------------
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$ git branch -r
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origin/HEAD
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origin/html
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origin/maint
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origin/man
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origin/master
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origin/next
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origin/pu
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origin/todo
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------------------------------------------------
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You cannot check out these remote-tracking branches, but you can
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examine them on a branch of your own, just as you would a tag:
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------------------------------------------------
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$ git checkout -b my-todo-copy origin/todo
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------------------------------------------------
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Note that the name "origin" is just the name that git uses by default
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to refer to the repository that you cloned from.
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[[how-git-stores-references]]
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Naming branches, tags, and other references
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-------------------------------------------
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Branches, remote-tracking branches, and tags are all references to
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commits. All references are named with a slash-separated path name
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starting with "refs"; the names we've been using so far are actually
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shorthand:
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- The branch "test" is short for "refs/heads/test".
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- The tag "v2.6.18" is short for "refs/tags/v2.6.18".
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- "origin/master" is short for "refs/remotes/origin/master".
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The full name is occasionally useful if, for example, there ever
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exists a tag and a branch with the same name.
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As another useful shortcut, if the repository "origin" posesses only
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a single branch, you can refer to that branch as just "origin".
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More generally, if you have defined a remote repository named
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"example", you can refer to the branch in that repository as
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"example". And for a repository with multiple branches, this will
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refer to the branch designated as the "HEAD" branch.
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For the complete list of paths which git checks for references, and
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the order it uses to decide which to choose when there are multiple
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references with the same shorthand name, see the "SPECIFYING
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REVISIONS" section of gitlink:git-rev-parse[1].
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|
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[[Updating-a-repository-with-git-fetch]]
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Updating a repository with git fetch
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|
------------------------------------
|
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|
|
Eventually the developer cloned from will do additional work in her
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repository, creating new commits and advancing the branches to point
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at the new commits.
|
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|
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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.
|
|
|
|
Fetching branches from other repositories
|
|
-----------------------------------------
|
|
|
|
You can also track branches from repositories other than the one you
|
|
cloned from, using gitlink:git-remote[1]:
|
|
|
|
-------------------------------------------------
|
|
$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
|
|
$ git fetch
|
|
* refs/remotes/linux-nfs/master: storing branch 'master' ...
|
|
commit: bf81b46
|
|
-------------------------------------------------
|
|
|
|
New remote-tracking branches will be stored under the shorthand name
|
|
that you gave "git remote add", in this case linux-nfs:
|
|
|
|
-------------------------------------------------
|
|
$ git branch -r
|
|
linux-nfs/master
|
|
origin/master
|
|
-------------------------------------------------
|
|
|
|
If you run "git fetch <remote>" later, the tracking branches for the
|
|
named <remote> will be updated.
|
|
|
|
If you examine the file .git/config, you will see that git has added
|
|
a new stanza:
|
|
|
|
-------------------------------------------------
|
|
$ cat .git/config
|
|
...
|
|
[remote "linux-nfs"]
|
|
url = git://linux-nfs.org/~bfields/git.git
|
|
fetch = +refs/heads/*:refs/remotes/linux-nfs-read/*
|
|
...
|
|
-------------------------------------------------
|
|
|
|
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
|
|
gitlink:git-config[1] for details.)
|
|
|
|
Exploring git history
|
|
=====================
|
|
|
|
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.
|
|
|
|
Git provides extremely flexible and fast tools for exploring the
|
|
history of a project.
|
|
|
|
We start with one specialized tool that is useful for finding the
|
|
commit that introduced a bug into a project.
|
|
|
|
How to use bisect to find a regression
|
|
--------------------------------------
|
|
|
|
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
|
|
gitlink:git-bisect[1] command can help you do this:
|
|
|
|
-------------------------------------------------
|
|
$ git bisect start
|
|
$ git bisect good v2.6.18
|
|
$ git bisect bad master
|
|
Bisecting: 3537 revisions left to test after this
|
|
[65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git bisect bad
|
|
Bisecting: 1769 revisions left to test after this
|
|
[7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
After about 13 tests (in this case), it will output the commit id of
|
|
the guilty commit. You can then examine the commit with
|
|
gitlink:git-show[1], find out who wrote it, and mail them your bug
|
|
report with the commit id. Finally, run
|
|
|
|
-------------------------------------------------
|
|
$ git bisect reset
|
|
-------------------------------------------------
|
|
|
|
to return you to the branch you were on before and delete the
|
|
temporary "bisect" branch.
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git bisect-visualize
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git reset --hard fb47ddb2db...
|
|
-------------------------------------------------
|
|
|
|
then test, run "bisect good" or "bisect bad" as appropriate, and
|
|
continue.
|
|
|
|
Naming commits
|
|
--------------
|
|
|
|
We have seen several ways of naming commits already:
|
|
|
|
- 40-hexdigit object name
|
|
- branch name: refers to the commit at the head of the given
|
|
branch
|
|
- tag name: refers to the commit pointed to by the given tag
|
|
(we've seen branches and tags are special cases of
|
|
<<how-git-stores-references,references>>).
|
|
- HEAD: refers to the head of the current branch
|
|
|
|
There are many more; see the "SPECIFYING REVISIONS" section of the
|
|
gitlink:git-rev-parse[1] man page for the complete list of ways to
|
|
name revisions. Some examples:
|
|
|
|
-------------------------------------------------
|
|
$ git show fb47ddb2 # the first few characters of the object name
|
|
# are usually enough to specify it uniquely
|
|
$ git show HEAD^ # the parent of the HEAD commit
|
|
$ git show HEAD^^ # the grandparent
|
|
$ git show HEAD~4 # the great-great-grandparent
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git show HEAD^1 # show the first parent of HEAD
|
|
$ git show HEAD^2 # show the second parent of HEAD
|
|
-------------------------------------------------
|
|
|
|
In addition to HEAD, there are several other special names for
|
|
commits:
|
|
|
|
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.
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git fetch git://example.com/proj.git theirbranch
|
|
-------------------------------------------------
|
|
|
|
the fetched commits will still be available from FETCH_HEAD.
|
|
|
|
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.
|
|
|
|
The gitlink:git-rev-parse[1] command is a low-level command that is
|
|
occasionally useful for translating some name for a commit to the object
|
|
name for that commit:
|
|
|
|
-------------------------------------------------
|
|
$ git rev-parse origin
|
|
e05db0fd4f31dde7005f075a84f96b360d05984b
|
|
-------------------------------------------------
|
|
|
|
Creating tags
|
|
-------------
|
|
|
|
We can also create a tag to refer to a particular commit; after
|
|
running
|
|
|
|
-------------------------------------------------
|
|
$ git-tag stable-1 1b2e1d63ff
|
|
-------------------------------------------------
|
|
|
|
You can use stable-1 to refer to the commit 1b2e1d63ff.
|
|
|
|
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 gitlink:git-tag[1] man
|
|
page for details.
|
|
|
|
Browsing revisions
|
|
------------------
|
|
|
|
The gitlink:git-log[1] 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:
|
|
|
|
-------------------------------------------------
|
|
$ git log v2.5.. # commits since (not reachable from) v2.5
|
|
$ git log test..master # commits reachable from master but not test
|
|
$ git log master..test # ...reachable from test but not master
|
|
$ git log master...test # ...reachable from either test or master,
|
|
# but not both
|
|
$ git log --since="2 weeks ago" # commits from the last 2 weeks
|
|
$ git log Makefile # commits which modify Makefile
|
|
$ git log fs/ # ... which modify any file under fs/
|
|
$ git log -S'foo()' # commits which add or remove any file data
|
|
# matching the string 'foo()'
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git log v2.5.. Makefile fs/
|
|
-------------------------------------------------
|
|
|
|
You can also ask git log to show patches:
|
|
|
|
-------------------------------------------------
|
|
$ git log -p
|
|
-------------------------------------------------
|
|
|
|
See the "--pretty" option in the gitlink:git-log[1] man page for more
|
|
display options.
|
|
|
|
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.
|
|
|
|
Generating diffs
|
|
----------------
|
|
|
|
You can generate diffs between any two versions using
|
|
gitlink:git-diff[1]:
|
|
|
|
-------------------------------------------------
|
|
$ git diff master..test
|
|
-------------------------------------------------
|
|
|
|
Sometimes what you want instead is a set of patches:
|
|
|
|
-------------------------------------------------
|
|
$ git format-patch master..test
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
Viewing old file versions
|
|
-------------------------
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git show v2.5:fs/locks.c
|
|
-------------------------------------------------
|
|
|
|
Before the colon may be anything that names a commit, and after it
|
|
may be any path to a file tracked by git.
|
|
|
|
Examples
|
|
--------
|
|
|
|
Check whether two branches point at the same history
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Suppose you want to check whether two branches point at the same point
|
|
in history.
|
|
|
|
-------------------------------------------------
|
|
$ git diff origin..master
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git rev-list origin
|
|
e05db0fd4f31dde7005f075a84f96b360d05984b
|
|
$ git rev-list master
|
|
e05db0fd4f31dde7005f075a84f96b360d05984b
|
|
-------------------------------------------------
|
|
|
|
Or you could recall that the ... operator selects all commits
|
|
contained reachable from either one reference or the other but not
|
|
both: so
|
|
|
|
-------------------------------------------------
|
|
$ git log origin...master
|
|
-------------------------------------------------
|
|
|
|
will return no commits when the two branches are equal.
|
|
|
|
Find first tagged version including a given fix
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Suppose you know that the commit e05db0fd fixed a certain problem.
|
|
You'd like to find the earliest tagged release that contains that
|
|
fix.
|
|
|
|
Of course, there may be more than one answer--if the history branched
|
|
after commit e05db0fd, then there could be multiple "earliest" tagged
|
|
releases.
|
|
|
|
You could just visually inspect the commits since e05db0fd:
|
|
|
|
-------------------------------------------------
|
|
$ gitk e05db0fd..
|
|
-------------------------------------------------
|
|
|
|
Or you can use gitlink:git-name-rev[1], which will give the commit a
|
|
name based on any tag it finds pointing to one of the commit's
|
|
descendants:
|
|
|
|
-------------------------------------------------
|
|
$ git name-rev e05db0fd
|
|
e05db0fd tags/v1.5.0-rc1^0~23
|
|
-------------------------------------------------
|
|
|
|
The gitlink:git-describe[1] command does the opposite, naming the
|
|
revision using a tag on which the given commit is based:
|
|
|
|
-------------------------------------------------
|
|
$ git describe e05db0fd
|
|
v1.5.0-rc0-ge05db0f
|
|
-------------------------------------------------
|
|
|
|
but that may sometimes help you guess which tags might come after the
|
|
given commit.
|
|
|
|
If you just want to verify whether a given tagged version contains a
|
|
given commit, you could use gitlink:git-merge-base[1]:
|
|
|
|
-------------------------------------------------
|
|
$ git merge-base e05db0fd v1.5.0-rc1
|
|
e05db0fd4f31dde7005f075a84f96b360d05984b
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
Alternatively, note that
|
|
|
|
-------------------------------------------------
|
|
$ git log v1.5.0-rc1..e05db0fd
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
As yet another alternative, the gitlink:git-show-branch[1] 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
|
|
|
|
-------------------------------------------------
|
|
$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
|
|
! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
|
|
available
|
|
! [v1.5.0-rc0] GIT v1.5.0 preview
|
|
! [v1.5.0-rc1] GIT v1.5.0-rc1
|
|
! [v1.5.0-rc2] GIT v1.5.0-rc2
|
|
...
|
|
-------------------------------------------------
|
|
|
|
then search for a line that looks like
|
|
|
|
-------------------------------------------------
|
|
+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
|
|
available
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
|
|
Developing with git
|
|
===================
|
|
|
|
Telling git your name
|
|
---------------------
|
|
|
|
Before creating any commits, you should introduce yourself to git. The
|
|
easiest way to do so is:
|
|
|
|
------------------------------------------------
|
|
$ cat >~/.gitconfig <<\EOF
|
|
[user]
|
|
name = Your Name Comes Here
|
|
email = you@yourdomain.example.com
|
|
EOF
|
|
------------------------------------------------
|
|
|
|
(See the "CONFIGURATION FILE" section of gitlink:git-config[1] for
|
|
details on the configuration file.)
|
|
|
|
|
|
Creating a new repository
|
|
-------------------------
|
|
|
|
Creating a new repository from scratch is very easy:
|
|
|
|
-------------------------------------------------
|
|
$ mkdir project
|
|
$ cd project
|
|
$ git init
|
|
-------------------------------------------------
|
|
|
|
If you have some initial content (say, a tarball):
|
|
|
|
-------------------------------------------------
|
|
$ tar -xzvf project.tar.gz
|
|
$ cd project
|
|
$ git init
|
|
$ git add . # include everything below ./ in the first commit:
|
|
$ git commit
|
|
-------------------------------------------------
|
|
|
|
[[how-to-make-a-commit]]
|
|
how to make a commit
|
|
--------------------
|
|
|
|
Creating a new commit takes three steps:
|
|
|
|
1. Making some changes to the working directory using your
|
|
favorite editor.
|
|
2. Telling git about your changes.
|
|
3. Creating the commit using the content you told git about
|
|
in step 2.
|
|
|
|
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."
|
|
|
|
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.
|
|
|
|
Modifying the index is easy:
|
|
|
|
To update the index with the new contents of a modified file, use
|
|
|
|
-------------------------------------------------
|
|
$ git add path/to/file
|
|
-------------------------------------------------
|
|
|
|
To add the contents of a new file to the index, use
|
|
|
|
-------------------------------------------------
|
|
$ git add path/to/file
|
|
-------------------------------------------------
|
|
|
|
To remove a file from the index and from the working tree,
|
|
|
|
-------------------------------------------------
|
|
$ git rm path/to/file
|
|
-------------------------------------------------
|
|
|
|
After each step you can verify that
|
|
|
|
-------------------------------------------------
|
|
$ git diff --cached
|
|
-------------------------------------------------
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git diff
|
|
-------------------------------------------------
|
|
|
|
shows the difference between the working tree and the index file.
|
|
|
|
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.
|
|
|
|
When you're ready, just run
|
|
|
|
-------------------------------------------------
|
|
$ git commit
|
|
-------------------------------------------------
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git show
|
|
-------------------------------------------------
|
|
|
|
As a special shortcut,
|
|
|
|
-------------------------------------------------
|
|
$ git commit -a
|
|
-------------------------------------------------
|
|
|
|
will update the index with any files that you've modified or removed
|
|
and create a commit, all in one step.
|
|
|
|
A number of commands are useful for keeping track of what you're
|
|
about to commit:
|
|
|
|
-------------------------------------------------
|
|
$ git diff --cached # difference between HEAD and the index; what
|
|
# would be commited if you ran "commit" now.
|
|
$ git diff # difference between the index file and your
|
|
# working directory; changes that would not
|
|
# be included if you ran "commit" now.
|
|
$ git status # a brief per-file summary of the above.
|
|
-------------------------------------------------
|
|
|
|
creating good commit messages
|
|
-----------------------------
|
|
|
|
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.
|
|
|
|
how to merge
|
|
------------
|
|
|
|
You can rejoin two diverging branches of development using
|
|
gitlink:git-merge[1]:
|
|
|
|
-------------------------------------------------
|
|
$ git merge branchname
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git pull . next
|
|
Trying really trivial in-index merge...
|
|
fatal: Merge requires file-level merging
|
|
Nope.
|
|
Merging HEAD with 77976da35a11db4580b80ae27e8d65caf5208086
|
|
Merging:
|
|
15e2162 world
|
|
77976da goodbye
|
|
found 1 common ancestor(s):
|
|
d122ed4 initial
|
|
Auto-merging file.txt
|
|
CONFLICT (content): Merge conflict in file.txt
|
|
Automatic merge failed; fix conflicts and then commit the result.
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
In more detail:
|
|
|
|
[[resolving-a-merge]]
|
|
Resolving a merge
|
|
-----------------
|
|
|
|
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.
|
|
|
|
Files with conflicts are marked specially in the index, so until you
|
|
resolve the problem and update the index, git commit will fail:
|
|
|
|
-------------------------------------------------
|
|
$ git commit
|
|
file.txt: needs merge
|
|
-------------------------------------------------
|
|
|
|
Also, git status will list those files as "unmerged".
|
|
|
|
All of the changes that git was able to merge automatically are
|
|
already added to the index file, so gitlink:git-diff[1] shows only
|
|
the conflicts. Also, it uses a somewhat unusual syntax:
|
|
|
|
-------------------------------------------------
|
|
$ git diff
|
|
diff --cc file.txt
|
|
index 802992c,2b60207..0000000
|
|
--- a/file.txt
|
|
+++ b/file.txt
|
|
@@@ -1,1 -1,1 +1,5 @@@
|
|
++<<<<<<< HEAD:file.txt
|
|
+Hello world
|
|
++=======
|
|
+ Goodbye
|
|
++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
The diff above shows the differences between the working-tree version
|
|
of file.txt and two previous version: 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:
|
|
|
|
-------------------------------------------------
|
|
$ git diff
|
|
diff --cc file.txt
|
|
index 802992c,2b60207..0000000
|
|
--- a/file.txt
|
|
+++ b/file.txt
|
|
@@@ -1,1 -1,1 +1,1 @@@
|
|
- Hello world
|
|
-Goodbye
|
|
++Goodbye world
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
The gitlink:git-log[1] command also provides special help for merges:
|
|
|
|
-------------------------------------------------
|
|
$ git log --merge
|
|
-------------------------------------------------
|
|
|
|
This will list all commits which exist only on HEAD or on MERGE_HEAD,
|
|
and which touch an unmerged file.
|
|
|
|
We can now add the resolved version to the index and commit:
|
|
|
|
-------------------------------------------------
|
|
$ git add file.txt
|
|
$ git commit
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
[[undoing-a-merge]]
|
|
undoing a merge
|
|
---------------
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git reset --hard HEAD
|
|
-------------------------------------------------
|
|
|
|
Or, if you've already commited the merge that you want to throw away,
|
|
|
|
-------------------------------------------------
|
|
$ git reset --hard HEAD^
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
Fast-forward merges
|
|
-------------------
|
|
|
|
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.
|
|
|
|
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
|
|
<<fast-forwards,fast forward>>; 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.
|
|
|
|
Fixing mistakes
|
|
---------------
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git reset --hard HEAD
|
|
-------------------------------------------------
|
|
|
|
If you make a commit that you later wish you hadn't, there are two
|
|
fundamentally different ways to fix the problem:
|
|
|
|
1. 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.
|
|
|
|
2. 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.
|
|
|
|
Fixing a mistake with a new commit
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Creating a new commit that reverts an earlier change is very easy;
|
|
just pass the gitlink:git-revert[1] command a reference to the bad
|
|
commit; for example, to revert the most recent commit:
|
|
|
|
-------------------------------------------------
|
|
$ git revert HEAD
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
You can also revert an earlier change, for example, the next-to-last:
|
|
|
|
-------------------------------------------------
|
|
$ git revert HEAD^
|
|
-------------------------------------------------
|
|
|
|
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 <<resolving-a-merge,
|
|
resolving a merge>>.
|
|
|
|
Fixing a mistake by editing history
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
If the problematic commit is the most recent commit, and you have not
|
|
yet made that commit public, then you may just
|
|
<<undoing-a-merge,destroy it using git-reset>>.
|
|
|
|
Alternatively, you
|
|
can edit the working directory and update the index to fix your
|
|
mistake, just as if you were going to <<how-to-make-a-commit,create a
|
|
new commit>>, then run
|
|
|
|
-------------------------------------------------
|
|
$ git commit --amend
|
|
-------------------------------------------------
|
|
|
|
which will replace the old commit by a new commit incorporating your
|
|
changes, giving you a chance to edit the old commit message first.
|
|
|
|
Again, you should never do this to a commit that may already have
|
|
been merged into another branch; use gitlink:git-revert[1] instead in
|
|
that case.
|
|
|
|
It is also possible to edit commits further back in the history, but
|
|
this is an advanced topic to be left for
|
|
<<cleaning-up-history,another chapter>>.
|
|
|
|
Checking out an old version of a file
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
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
|
|
gitlink:git-checkout[1]. We've used git checkout before to switch
|
|
branches, but it has quite different behavior if it is given a path
|
|
name: the command
|
|
|
|
-------------------------------------------------
|
|
$ git checkout HEAD^ path/to/file
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
If you just want to look at an old version of the file, without
|
|
modifying the working directory, you can do that with
|
|
gitlink:git-show[1]:
|
|
|
|
-------------------------------------------------
|
|
$ git show HEAD^ path/to/file
|
|
-------------------------------------------------
|
|
|
|
which will display the given version of the file.
|
|
|
|
Ensuring good performance
|
|
-------------------------
|
|
|
|
On large repositories, git depends on compression to keep the history
|
|
information from taking up to much space on disk or in memory.
|
|
|
|
This compression is not performed automatically. Therefore you
|
|
should occasionally run gitlink:git-gc[1]:
|
|
|
|
-------------------------------------------------
|
|
$ git gc
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
Ensuring reliability
|
|
--------------------
|
|
|
|
Checking the repository for corruption
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The gitlink:git-fsck[1] 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:
|
|
|
|
-------------------------------------------------
|
|
$ git fsck
|
|
dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
|
|
dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
|
|
dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
|
|
dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
|
|
dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
|
|
dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
|
|
dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
|
|
dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
|
|
...
|
|
-------------------------------------------------
|
|
|
|
Dangling objects are objects that are harmless, but also unnecessary;
|
|
you can remove them at any time with gitlink:git-prune[1] or the --prune
|
|
option to gitlink:git-gc[1]:
|
|
|
|
-------------------------------------------------
|
|
$ git gc --prune
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
For more about dangling objects, see <<dangling-objects>>.
|
|
|
|
|
|
Recovering lost changes
|
|
~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Reflogs
|
|
^^^^^^^
|
|
|
|
Say you modify a branch with gitlink:git-reset[1] --hard, and then
|
|
realize that the branch was the only reference you had to that point in
|
|
history.
|
|
|
|
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,
|
|
|
|
-------------------------------------------------
|
|
$ git log master@{1}
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git show master@{2} # See where the branch pointed 2,
|
|
$ git show master@{3} # 3, ... changes ago.
|
|
$ gitk master@{yesterday} # See where it pointed yesterday,
|
|
$ gitk master@{"1 week ago"} # ... or last week
|
|
-------------------------------------------------
|
|
|
|
The reflogs are kept by default for 30 days, after which they may be
|
|
pruned. See gitlink:git-reflog[1] and gitlink:git-gc[1] to learn
|
|
how to control this pruning, and see the "SPECIFYING REVISIONS"
|
|
section of gitlink:git-rev-parse[1] for details.
|
|
|
|
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.
|
|
|
|
Examining dangling objects
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
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 pointed you. 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":
|
|
|
|
-------------------------------------------------
|
|
$ git fsck
|
|
dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
|
|
dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
|
|
dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
|
|
...
|
|
-------------------------------------------------
|
|
|
|
You can examine
|
|
one of those dangling commits with, for example,
|
|
|
|
------------------------------------------------
|
|
$ gitk 7281251ddd --not --all
|
|
------------------------------------------------
|
|
|
|
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 gotten dropped.)
|
|
|
|
If you decide you want the history back, you can always create a new
|
|
reference pointing to it, for example, a new branch:
|
|
|
|
------------------------------------------------
|
|
$ git branch recovered-branch 7281251ddd
|
|
------------------------------------------------
|
|
|
|
|
|
Sharing development with others
|
|
===============================
|
|
|
|
[[getting-updates-with-git-pull]]
|
|
Getting updates with git pull
|
|
-----------------------------
|
|
|
|
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.
|
|
|
|
We have already seen <<Updating-a-repository-with-git-fetch,how to
|
|
keep remote tracking branches up to date>> with gitlink:git-fetch[1],
|
|
and how to merge two branches. So you can merge in changes from the
|
|
original repository's master branch with:
|
|
|
|
-------------------------------------------------
|
|
$ git fetch
|
|
$ git merge origin/master
|
|
-------------------------------------------------
|
|
|
|
However, the gitlink:git-pull[1] command provides a way to do this in
|
|
one step:
|
|
|
|
-------------------------------------------------
|
|
$ git pull origin master
|
|
-------------------------------------------------
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git pull
|
|
-------------------------------------------------
|
|
|
|
See the descriptions of the branch.<name>.remote and
|
|
branch.<name>.merge options in gitlink:git-config[1] to learn
|
|
how to control these defaults depending on the current branch.
|
|
|
|
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.
|
|
|
|
(But note that no such commit will be created in the case of a
|
|
<<fast-forwards,fast forward>>; instead, your branch will just be
|
|
updated to point to the latest commit from the upstream branch).
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git pull . branch
|
|
$ git merge branch
|
|
-------------------------------------------------
|
|
|
|
are roughly equivalent. The former is actually very commonly used.
|
|
|
|
Submitting patches to a project
|
|
-------------------------------
|
|
|
|
If you just have a few changes, the simplest way to submit them may
|
|
just be to send them as patches in email:
|
|
|
|
First, use gitlink:git-format-patch[1]; for example:
|
|
|
|
-------------------------------------------------
|
|
$ git format-patch origin
|
|
-------------------------------------------------
|
|
|
|
will produce a numbered series of files in the current directory, one
|
|
for each patch in the current branch but not in origin/HEAD.
|
|
|
|
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 gitlink:git-send-email[1] script to automate the process.
|
|
Consult the mailing list for your project first to determine how they
|
|
prefer such patches be handled.
|
|
|
|
Importing patches to a project
|
|
------------------------------
|
|
|
|
Git also provides a tool called gitlink:git-am[1] (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
|
|
|
|
-------------------------------------------------
|
|
$ git am -3 patches.mbox
|
|
-------------------------------------------------
|
|
|
|
Git will apply each patch in order; if any conflicts are found, it
|
|
will stop, and you can fix the conflicts as described in
|
|
"<<resolving-a-merge,Resolving a merge>>". (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.)
|
|
|
|
Once the index is updated with the results of the conflict
|
|
resolution, instead of creating a new commit, just run
|
|
|
|
-------------------------------------------------
|
|
$ git am --resolved
|
|
-------------------------------------------------
|
|
|
|
and git will create the commit for you and continue applying the
|
|
remaining patches from the mailbox.
|
|
|
|
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.
|
|
|
|
[[setting-up-a-public-repository]]
|
|
Setting up a public repository
|
|
------------------------------
|
|
|
|
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 "<<getting-updates-with-git-pull, Getting
|
|
updates with git pull>>".
|
|
|
|
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 command (gitlink:git-clone[1],
|
|
git-fetch[1], git-pull[1], etc.) which accept a URL as an argument
|
|
will also accept a local file patch; so, for example, you can
|
|
use
|
|
|
|
-------------------------------------------------
|
|
$ git clone /path/to/repository
|
|
$ git pull /path/to/other/repository
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
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:
|
|
|
|
you push
|
|
your personal repo ------------------> your public repo
|
|
^ |
|
|
| |
|
|
| you pull | they pull
|
|
| |
|
|
| |
|
|
| they push V
|
|
their public repo <------------------- their repo
|
|
|
|
Now, assume your personal repository is in the directory ~/proj. We
|
|
first create a new clone of the repository:
|
|
|
|
-------------------------------------------------
|
|
$ git clone --bare proj-clone.git
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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
|
|
"<<pushing-changes-to-a-public-repository,Pushing changes to a public
|
|
repository>>", below.
|
|
|
|
Otherwise, the following sections explain how to export your newly
|
|
created public repository:
|
|
|
|
[[exporting-via-http]]
|
|
Exporting a git repository via http
|
|
-----------------------------------
|
|
|
|
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.
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ mv proj.git /home/you/public_html/proj.git
|
|
$ cd proj.git
|
|
$ git update-server-info
|
|
$ chmod a+x hooks/post-update
|
|
-------------------------------------------------
|
|
|
|
(For an explanation of the last two lines, see
|
|
gitlink:git-update-server-info[1], and the documentation
|
|
link:hooks.txt[Hooks used by git].)
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git clone http://yourserver.com/~you/proj.git
|
|
-------------------------------------------------
|
|
|
|
(See also
|
|
link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
|
|
for a slightly more sophisticated setup using WebDAV which also
|
|
allows pushing over http.)
|
|
|
|
[[exporting-via-git]]
|
|
Exporting a git repository via the git protocol
|
|
-----------------------------------------------
|
|
|
|
This is the preferred method.
|
|
|
|
For now, we refer you to the gitlink:git-daemon[1] man page for
|
|
instructions. (See especially the examples section.)
|
|
|
|
[[pushing-changes-to-a-public-repository]]
|
|
Pushing changes to a public repository
|
|
--------------------------------------
|
|
|
|
Note that the two techniques outline above (exporting via
|
|
<<exporting-via-http,http>> or <<exporting-via-git,git>>) 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.
|
|
|
|
The simplest way to do this is using gitlink:git-push[1] and ssh; to
|
|
update the remote branch named "master" with the latest state of your
|
|
branch named "master", run
|
|
|
|
-------------------------------------------------
|
|
$ git push ssh://yourserver.com/~you/proj.git master:master
|
|
-------------------------------------------------
|
|
|
|
or just
|
|
|
|
-------------------------------------------------
|
|
$ git push ssh://yourserver.com/~you/proj.git master
|
|
-------------------------------------------------
|
|
|
|
As with git-fetch, git-push will complain if this does not result in
|
|
a <<fast-forwards,fast forward>>. 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:
|
|
|
|
-------------------------------------------------
|
|
$ git push ssh://yourserver.com/~you/proj.git +master
|
|
-------------------------------------------------
|
|
|
|
As with git-fetch, you may also set up configuration options to
|
|
save typing; so, for example, after
|
|
|
|
-------------------------------------------------
|
|
$ cat >.git/config <<EOF
|
|
[remote "public-repo"]
|
|
url = ssh://yourserver.com/~you/proj.git
|
|
EOF
|
|
-------------------------------------------------
|
|
|
|
you should be able to perform the above push with just
|
|
|
|
-------------------------------------------------
|
|
$ git push public-repo master
|
|
-------------------------------------------------
|
|
|
|
See the explanations of the remote.<name>.url, branch.<name>.remote,
|
|
and remote.<name>.push options in gitlink:git-config[1] for
|
|
details.
|
|
|
|
Setting up a shared repository
|
|
------------------------------
|
|
|
|
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
|
|
link:cvs-migration.txt[git for CVS users] for instructions on how to
|
|
set this up.
|
|
|
|
Allow web browsing of a repository
|
|
----------------------------------
|
|
|
|
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.
|
|
|
|
Examples
|
|
--------
|
|
|
|
TODO: topic branches, typical roles as in everyday.txt, ?
|
|
|
|
|
|
[[cleaning-up-history]]
|
|
Rewriting history and maintaining patch series
|
|
==============================================
|
|
|
|
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.
|
|
|
|
However, there is a situation in which it can be useful to violate this
|
|
assumption.
|
|
|
|
Creating the perfect patch series
|
|
---------------------------------
|
|
|
|
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.
|
|
|
|
If you present all of your changes as a single patch (or commit), they
|
|
may find it is too much to digest all at once.
|
|
|
|
If you present them with the entire history of your work, complete with
|
|
mistakes, corrections, and dead ends, they may be overwhelmed.
|
|
|
|
So the ideal is usually to produce a series of patches such that:
|
|
|
|
1. Each patch can be applied in order.
|
|
|
|
2. Each patch includes a single logical change, together with a
|
|
message explaining the change.
|
|
|
|
3. 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.
|
|
|
|
4. The complete series produces the same end result as your own
|
|
(probably much messier!) development process did.
|
|
|
|
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.
|
|
|
|
Keeping a patch series up to date using git-rebase
|
|
--------------------------------------------------
|
|
|
|
Suppose you have a series of commits in a branch "mywork", which
|
|
originally branched off from "origin".
|
|
|
|
Suppose you create a branch "mywork" on a remote-tracking branch
|
|
"origin", and created some commits on top of it:
|
|
|
|
-------------------------------------------------
|
|
$ git checkout -b mywork origin
|
|
$ vi file.txt
|
|
$ git commit
|
|
$ vi otherfile.txt
|
|
$ git commit
|
|
...
|
|
-------------------------------------------------
|
|
|
|
You have performed no merges into mywork, so it is just a simple linear
|
|
sequence of patches on top of "origin":
|
|
|
|
|
|
o--o--o <-- origin
|
|
\
|
|
o--o--o <-- mywork
|
|
|
|
Some more interesting work has been done in the upstream project, and
|
|
"origin" has advanced:
|
|
|
|
o--o--O--o--o--o <-- origin
|
|
\
|
|
a--b--c <-- mywork
|
|
|
|
At this point, you could use "pull" to merge your changes back in;
|
|
the result would create a new merge commit, like this:
|
|
|
|
|
|
o--o--O--o--o--o <-- origin
|
|
\ \
|
|
a--b--c--m <-- mywork
|
|
|
|
However, if you prefer to keep the history in mywork a simple series of
|
|
commits without any merges, you may instead choose to use
|
|
gitlink:git-rebase[1]:
|
|
|
|
-------------------------------------------------
|
|
$ git checkout mywork
|
|
$ git rebase origin
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
|
|
o--o--O--o--o--o <-- origin
|
|
\
|
|
a'--b'--c' <-- mywork
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git rebase --continue
|
|
-------------------------------------------------
|
|
|
|
and git will continue applying the rest of the patches.
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git rebase --abort
|
|
-------------------------------------------------
|
|
|
|
Reordering or selecting from a patch series
|
|
-------------------------------------------
|
|
|
|
Given one existing commit, the gitlink:git-cherry-pick[1] 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:
|
|
|
|
-------------------------------------------------
|
|
$ git checkout -b mywork-new origin
|
|
$ gitk origin..mywork &
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
Another technique is to use git-format-patch to create a series of
|
|
patches, then reset the state to before the patches:
|
|
|
|
-------------------------------------------------
|
|
$ git format-patch origin
|
|
$ git reset --hard origin
|
|
-------------------------------------------------
|
|
|
|
Then modify, reorder, or eliminate patches as preferred before applying
|
|
them again with gitlink:git-am[1].
|
|
|
|
Other tools
|
|
-----------
|
|
|
|
There are numerous other tools, such as stgit, which exist for the
|
|
purpose of maintaining a patch series. These are out of the scope of
|
|
this manual.
|
|
|
|
Problems with rewriting history
|
|
-------------------------------
|
|
|
|
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:
|
|
|
|
o--o--O--o--o--o <-- origin
|
|
\ \
|
|
t--t--t--m <-- their branch:
|
|
|
|
Then suppose you modify the last three commits:
|
|
|
|
o--o--o <-- new head of origin
|
|
/
|
|
o--o--O--o--o--o <-- old head of origin
|
|
|
|
If we examined all this history together in one repository, it will
|
|
look like:
|
|
|
|
o--o--o <-- new head of origin
|
|
/
|
|
o--o--O--o--o--o <-- old head of origin
|
|
\ \
|
|
t--t--t--m <-- their branch:
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
For true distributed development that supports proper merging,
|
|
published branches should never be rewritten.
|
|
|
|
Advanced branch management
|
|
==========================
|
|
|
|
Fetching individual branches
|
|
----------------------------
|
|
|
|
Instead of using gitlink:git-remote[1], you can also choose just
|
|
to update one branch at a time, and to store it locally under an
|
|
arbitrary name:
|
|
|
|
-------------------------------------------------
|
|
$ git fetch origin todo:my-todo-work
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
You can also fetch branches from other repositories; so
|
|
|
|
-------------------------------------------------
|
|
$ git fetch git://example.com/proj.git master:example-master
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
[[fast-forwards]]
|
|
Understanding git history: fast-forwards
|
|
----------------------------------------
|
|
|
|
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".
|
|
|
|
A fast forward looks something like this:
|
|
|
|
o--o--o--o <-- old head of the branch
|
|
\
|
|
o--o--o <-- new head of the branch
|
|
|
|
|
|
In some cases it is possible that the new head will *not* 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:
|
|
|
|
o--o--o--o--a--b <-- old head of the branch
|
|
\
|
|
o--o--o <-- new head of the branch
|
|
|
|
|
|
|
|
In this case, "git fetch" will fail, and print out a warning.
|
|
|
|
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.
|
|
|
|
Forcing git fetch to do non-fast-forward updates
|
|
------------------------------------------------
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git fetch git://example.com/proj.git +master:refs/remotes/example/master
|
|
-------------------------------------------------
|
|
|
|
Note the addition of the "+" sign. Be aware that commits which the
|
|
old version of example/master pointed at may be lost, as we saw in
|
|
the previous section.
|
|
|
|
Configuring remote branches
|
|
---------------------------
|
|
|
|
We saw above that "origin" is just a shortcut to refer to the
|
|
repository which you originally cloned from. This information is
|
|
stored in git configuration variables, which you can see using
|
|
gitlink:git-config[1]:
|
|
|
|
-------------------------------------------------
|
|
$ git config -l
|
|
core.repositoryformatversion=0
|
|
core.filemode=true
|
|
core.logallrefupdates=true
|
|
remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
|
|
remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
|
|
branch.master.remote=origin
|
|
branch.master.merge=refs/heads/master
|
|
-------------------------------------------------
|
|
|
|
If there are other repositories that you also use frequently, you can
|
|
create similar configuration options to save typing; for example,
|
|
after
|
|
|
|
-------------------------------------------------
|
|
$ git config remote.example.url git://example.com/proj.git
|
|
-------------------------------------------------
|
|
|
|
then the following two commands will do the same thing:
|
|
|
|
-------------------------------------------------
|
|
$ git fetch git://example.com/proj.git master:refs/remotes/example/master
|
|
$ git fetch example master:refs/remotes/example/master
|
|
-------------------------------------------------
|
|
|
|
Even better, if you add one more option:
|
|
|
|
-------------------------------------------------
|
|
$ git config remote.example.fetch master:refs/remotes/example/master
|
|
-------------------------------------------------
|
|
|
|
then the following commands will all do the same thing:
|
|
|
|
-------------------------------------------------
|
|
$ git fetch git://example.com/proj.git master:ref/remotes/example/master
|
|
$ git fetch example master:ref/remotes/example/master
|
|
$ git fetch example example/master
|
|
$ git fetch example
|
|
-------------------------------------------------
|
|
|
|
You can also add a "+" to force the update each time:
|
|
|
|
-------------------------------------------------
|
|
$ git config remote.example.fetch +master:ref/remotes/example/master
|
|
-------------------------------------------------
|
|
|
|
Don't do this unless you're sure you won't mind "git fetch" possibly
|
|
throwing away commits on mybranch.
|
|
|
|
Also note that all of the above configuration can be performed by
|
|
directly editing the file .git/config instead of using
|
|
gitlink:git-config[1].
|
|
|
|
See gitlink:git-config[1] for more details on the configuration
|
|
options mentioned above.
|
|
|
|
|
|
Git internals
|
|
=============
|
|
|
|
There are two object abstractions: the "object database", and the
|
|
"current directory cache" aka "index".
|
|
|
|
The Object Database
|
|
-------------------
|
|
|
|
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.
|
|
|
|
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".
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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 `sha1sum` 'file' does not match the object name
|
|
for 'file'.
|
|
(Historical note: in the dawn of the age of git the hash
|
|
was the sha1 of the 'compressed' object.)
|
|
|
|
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>.
|
|
|
|
The structured objects can further have their structure and
|
|
connectivity to other objects verified. This is generally done with
|
|
the `git-fsck` 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).
|
|
|
|
The object types in some more detail:
|
|
|
|
Blob Object
|
|
-----------
|
|
|
|
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 'is'
|
|
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").
|
|
|
|
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.
|
|
|
|
A blob is typically created when gitlink:git-update-index[1]
|
|
is run, and its data can be accessed by gitlink:git-cat-file[1].
|
|
|
|
Tree Object
|
|
-----------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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 'came' from.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
A tree is created with gitlink:git-write-tree[1] and
|
|
its data can be accessed by gitlink:git-ls-tree[1].
|
|
Two trees can be compared with gitlink:git-diff-tree[1].
|
|
|
|
Commit Object
|
|
-------------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
A commit is created with gitlink:git-commit-tree[1] and
|
|
its data can be accessed by gitlink:git-cat-file[1].
|
|
|
|
Trust
|
|
-----
|
|
|
|
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 'can' 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.
|
|
|
|
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.
|
|
|
|
So to introduce some real trust in the system, the only thing you need
|
|
to do is to digitally sign just 'one' 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.
|
|
|
|
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.
|
|
|
|
To assist in this, git also provides the tag object...
|
|
|
|
Tag Object
|
|
----------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
A tag is created with gitlink:git-mktag[1],
|
|
its data can be accessed by gitlink:git-cat-file[1],
|
|
and the signature can be verified by
|
|
gitlink:git-verify-tag[1].
|
|
|
|
|
|
The "index" aka "Current Directory Cache"
|
|
-----------------------------------------
|
|
|
|
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.
|
|
|
|
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 'not' be consistent with the directory
|
|
hierarchy), but it has three very important attributes:
|
|
|
|
'(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)'
|
|
|
|
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)
|
|
|
|
'(b) it has efficient methods for finding inconsistencies between that
|
|
cached state ("tree object waiting to be instantiated") and the
|
|
current state.'
|
|
|
|
'(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.'
|
|
|
|
Those are the three ONLY 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.
|
|
|
|
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.
|
|
|
|
|
|
|
|
The Workflow
|
|
------------
|
|
|
|
Generally, all "git" operations work on the index file. Some operations
|
|
work *purely* 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:
|
|
|
|
working directory -> index
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
You update the index with information from the working directory with
|
|
the gitlink:git-update-index[1] command. You
|
|
generally update the index information by just specifying the filename
|
|
you want to update, like so:
|
|
|
|
-------------------------------------------------
|
|
$ git-update-index filename
|
|
-------------------------------------------------
|
|
|
|
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.
|
|
|
|
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 `--remove` and `--add` flags respectively.
|
|
|
|
NOTE! A `--remove` flag does 'not' 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 `--remove` 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.
|
|
|
|
As a special case, you can also do `git-update-index --refresh`, which
|
|
will refresh the "stat" information of each index to match the current
|
|
stat information. It will 'not' 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.
|
|
|
|
index -> object database
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
You write your current index file to a "tree" object with the program
|
|
|
|
-------------------------------------------------
|
|
$ git-write-tree
|
|
-------------------------------------------------
|
|
|
|
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:
|
|
|
|
object database -> index
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git-read-tree <sha1 of tree>
|
|
-------------------------------------------------
|
|
|
|
and your index file will now be equivalent to the tree that you saved
|
|
earlier. However, that is only your 'index' file: your working
|
|
directory contents have not been modified.
|
|
|
|
index -> working directory
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
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. `git-update-index`).
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git-checkout-index filename
|
|
-------------------------------------------------
|
|
|
|
or, if you want to check out all of the index, use `-a`.
|
|
|
|
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 ('before' the "-a" flag or the filename) to
|
|
'force' the checkout.
|
|
|
|
|
|
Finally, there are a few odds and ends which are not purely moving
|
|
from one representation to the other:
|
|
|
|
Tying it all together
|
|
~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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:
|
|
|
|
-------------------------------------------------
|
|
$ git-commit-tree <tree> -p <parent> [-p <parent2> ..]
|
|
-------------------------------------------------
|
|
|
|
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).
|
|
|
|
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 `HEAD` 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 `.git/HEAD`, so that we can always see
|
|
what the last committed state was.
|
|
|
|
Here is an ASCII art by Jon Loeliger that illustrates how
|
|
various pieces fit together.
|
|
|
|
------------
|
|
|
|
commit-tree
|
|
commit obj
|
|
+----+
|
|
| |
|
|
| |
|
|
V V
|
|
+-----------+
|
|
| Object DB |
|
|
| Backing |
|
|
| Store |
|
|
+-----------+
|
|
^
|
|
write-tree | |
|
|
tree obj | |
|
|
| | read-tree
|
|
| | tree obj
|
|
V
|
|
+-----------+
|
|
| Index |
|
|
| "cache" |
|
|
+-----------+
|
|
update-index ^
|
|
blob obj | |
|
|
| |
|
|
checkout-index -u | | checkout-index
|
|
stat | | blob obj
|
|
V
|
|
+-----------+
|
|
| Working |
|
|
| Directory |
|
|
+-----------+
|
|
|
|
------------
|
|
|
|
|
|
Examining the data
|
|
------------------
|
|
|
|
You can examine the data represented in the object database and the
|
|
index with various helper tools. For every object, you can use
|
|
gitlink:git-cat-file[1] to examine details about the
|
|
object:
|
|
|
|
-------------------------------------------------
|
|
$ git-cat-file -t <objectname>
|
|
-------------------------------------------------
|
|
|
|
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
|
|
|
|
-------------------------------------------------
|
|
$ git-cat-file blob|tree|commit|tag <objectname>
|
|
-------------------------------------------------
|
|
|
|
to show its contents. NOTE! Trees have binary content, and as a result
|
|
there is a special helper for showing that content, called
|
|
`git-ls-tree`, which turns the binary content into a more easily
|
|
readable form.
|
|
|
|
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 `.git/HEAD`,
|
|
you can do
|
|
|
|
-------------------------------------------------
|
|
$ git-cat-file commit HEAD
|
|
-------------------------------------------------
|
|
|
|
to see what the top commit was.
|
|
|
|
Merging multiple trees
|
|
----------------------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
To get the "base" for the merge, you first look up the common parent
|
|
of two commits with
|
|
|
|
-------------------------------------------------
|
|
$ git-merge-base <commit1> <commit2>
|
|
-------------------------------------------------
|
|
|
|
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)
|
|
|
|
-------------------------------------------------
|
|
$ git-cat-file commit <commitname> | head -1
|
|
-------------------------------------------------
|
|
|
|
since the tree object information is always the first line in a commit
|
|
object.
|
|
|
|
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).
|
|
|
|
To do the merge, do
|
|
|
|
-------------------------------------------------
|
|
$ git-read-tree -m -u <origtree> <yourtree> <targettree>
|
|
-------------------------------------------------
|
|
|
|
which will do all trivial merge operations for you directly in the
|
|
index file, and you can just write the result out with
|
|
`git-write-tree`.
|
|
|
|
|
|
Merging multiple trees, continued
|
|
---------------------------------
|
|
|
|
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 'NOT' 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.
|
|
|
|
You can examine such index state with `git-ls-files --unmerged`
|
|
command. An example:
|
|
|
|
------------------------------------------------
|
|
$ git-read-tree -m $orig HEAD $target
|
|
$ git-ls-files --unmerged
|
|
100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c
|
|
100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c
|
|
100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c
|
|
------------------------------------------------
|
|
|
|
Each line of the `git-ls-files --unmerged` output begins with
|
|
the blob mode bits, blob SHA1, 'stage number', and the
|
|
filename. The 'stage number' is git's way to say which tree it
|
|
came from: stage 1 corresponds to `$orig` tree, stage 2 `HEAD`
|
|
tree, and stage3 `$target` tree.
|
|
|
|
Earlier we said that trivial merges are done inside
|
|
`git-read-tree -m`. For example, if the file did not change
|
|
from `$orig` to `HEAD` nor `$target`, or if the file changed
|
|
from `$orig` to `HEAD` and `$orig` to `$target` the same way,
|
|
obviously the final outcome is what is in `HEAD`. What the
|
|
above example shows is that file `hello.c` was changed from
|
|
`$orig` to `HEAD` and `$orig` to `$target` in a different way.
|
|
You could resolve this by running your favorite 3-way merge
|
|
program, e.g. `diff3` or `merge`, on the blob objects from
|
|
these three stages yourself, like this:
|
|
|
|
------------------------------------------------
|
|
$ git-cat-file blob 263414f... >hello.c~1
|
|
$ git-cat-file blob 06fa6a2... >hello.c~2
|
|
$ git-cat-file blob cc44c73... >hello.c~3
|
|
$ merge hello.c~2 hello.c~1 hello.c~3
|
|
------------------------------------------------
|
|
|
|
This would leave the merge result in `hello.c~2` 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:
|
|
|
|
-------------------------------------------------
|
|
$ mv -f hello.c~2 hello.c
|
|
$ git-update-index hello.c
|
|
-------------------------------------------------
|
|
|
|
When a path is in unmerged state, running `git-update-index` for
|
|
that path tells git to mark the path resolved.
|
|
|
|
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 `git-cat-file`
|
|
for this. There is `git-merge-index` program that extracts the
|
|
stages to temporary files and calls a "merge" script on it:
|
|
|
|
-------------------------------------------------
|
|
$ git-merge-index git-merge-one-file hello.c
|
|
-------------------------------------------------
|
|
|
|
and that is what higher level `git merge -s resolve` is implemented with.
|
|
|
|
How git stores objects efficiently: pack files
|
|
----------------------------------------------
|
|
|
|
We've seen how git stores each object in a file named after the
|
|
object's SHA1 hash.
|
|
|
|
Unfortunately this system becomes inefficient once a project has a
|
|
lot of objects. Try this on an old project:
|
|
|
|
------------------------------------------------
|
|
$ git count-objects
|
|
6930 objects, 47620 kilobytes
|
|
------------------------------------------------
|
|
|
|
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.
|
|
|
|
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 link:technical/pack-format.txt[technical/pack-format.txt].
|
|
|
|
To put the loose objects into a pack, just run git repack:
|
|
|
|
------------------------------------------------
|
|
$ git repack
|
|
Generating pack...
|
|
Done counting 6020 objects.
|
|
Deltifying 6020 objects.
|
|
100% (6020/6020) done
|
|
Writing 6020 objects.
|
|
100% (6020/6020) done
|
|
Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
|
|
Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
|
|
------------------------------------------------
|
|
|
|
You can then run
|
|
|
|
------------------------------------------------
|
|
$ git prune
|
|
------------------------------------------------
|
|
|
|
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
|
|
|
|
------------------------------------------------
|
|
$ git count-objects
|
|
0 objects, 0 kilobytes
|
|
------------------------------------------------
|
|
|
|
Although the object files are gone, any commands that refer to those
|
|
objects will work exactly as they did before.
|
|
|
|
The gitlink:git-gc[1] command performs packing, pruning, and more for
|
|
you, so is normally the only high-level command you need.
|
|
|
|
[[dangling-objects]]
|
|
Dangling objects
|
|
----------------
|
|
|
|
The gitlink:git-fsck[1] command will sometimes complain about dangling
|
|
objects. They are not a problem.
|
|
|
|
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
|
|
<<cleaning-up-history>>. 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.
|
|
|
|
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 *updated* 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.
|
|
|
|
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.
|
|
|
|
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).
|
|
|
|
For commits, the most useful thing to do with dangling objects tends to
|
|
be to do a simple
|
|
|
|
------------------------------------------------
|
|
$ gitk <dangling-commit-sha-goes-here> --not --all
|
|
------------------------------------------------
|
|
|
|
For blobs and trees, you can't do the same, but you can examine them.
|
|
You can just do
|
|
|
|
------------------------------------------------
|
|
$ git show <dangling-blob/tree-sha-goes-here>
|
|
------------------------------------------------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
Anyway, once you are sure that you're not interested in any dangling
|
|
state, you can just prune all unreachable objects:
|
|
|
|
------------------------------------------------
|
|
$ git prune
|
|
------------------------------------------------
|
|
|
|
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.
|
|
|
|
(The same is true of "git-fsck" itself, btw - but since
|
|
git-fsck never actually *changes* 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 *BAD* idea).
|
|
|
|
Glossary of git terms
|
|
=====================
|
|
|
|
include::glossary.txt[]
|
|
|
|
Notes and todo list for this manual
|
|
===================================
|
|
|
|
This is a work in progress.
|
|
|
|
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"
|
|
|
|
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.
|
|
|
|
Say something about .gitignore.
|
|
|
|
Scan Documentation/ for other stuff left out; in particular:
|
|
howto's
|
|
some of technical/?
|
|
hooks
|
|
list of commands in gitlink:git[1]
|
|
|
|
Scan email archives for other stuff left out
|
|
|
|
Scan man pages to see if any assume more background than this manual
|
|
provides.
|
|
|
|
Simplify beginning by suggesting disconnected head instead of
|
|
temporary branch creation?
|
|
|
|
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.
|
|
|
|
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?
|
|
|
|
Include cross-references to the glossary, where appropriate.
|
|
|
|
Document shallow clones? See draft 1.5.0 release notes for some
|
|
documentation.
|
|
|
|
Add a section on working with other version control systems, including
|
|
CVS, Subversion, and just imports of series of release tarballs.
|
|
|
|
More details on gitweb?
|
|
|
|
Write a chapter on using plumbing and writing scripts.
|