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gitrepository-layout - Git Repository Layout
A Git repository comes in two different flavours: • a .git directory at the root of the working tree; • a <project>.git directory that is a bare repository (i.e. without its own working tree), that is typically used for exchanging histories with others by pushing into it and fetching from it. Note: Also you can have a plain text file .git at the root of your working tree, containing gitdir: <path> to point at the real directory that has the repository. This mechanism is often used for a working tree of a submodule checkout, to allow you in the containing superproject to git checkout a branch that does not have the submodule. The checkout has to remove the entire submodule working tree, without losing the submodule repository. These things may exist in a Git repository. objects Object store associated with this repository. Usually an object store is self sufficient (i.e. all the objects that are referred to by an object found in it are also found in it), but there are a few ways to violate it. 1. You could have an incomplete but locally usable repository by creating a shallow clone. See git-clone(1). 2. You could be using the objects/info/alternates or $GIT_ALTERNATE_OBJECT_DIRECTORIES mechanisms to borrow objects from other object stores. A repository with this kind of incomplete object store is not suitable to be published for use with dumb transports but otherwise is OK as long as objects/info/alternates points at the object stores it borrows from. This directory is ignored if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/objects" will be used instead. objects/[0-9a-f][0-9a-f] A newly created object is stored in its own file. The objects are splayed over 256 subdirectories using the first two characters of the sha1 object name to keep the number of directory entries in objects itself to a manageable number. Objects found here are often called unpacked (or loose) objects. objects/pack Packs (files that store many objects in compressed form, along with index files to allow them to be randomly accessed) are found in this directory. objects/info Additional information about the object store is recorded in this directory. objects/info/packs This file is to help dumb transports discover what packs are available in this object store. Whenever a pack is added or removed, git update-server-info should be run to keep this file up to date if the repository is published for dumb transports. git repack does this by default. objects/info/alternates This file records paths to alternate object stores that this object store borrows objects from, one pathname per line. Note that not only native Git tools use it locally, but the HTTP fetcher also tries to use it remotely; this will usually work if you have relative paths (relative to the object database, not to the repository!) in your alternates file, but it will not work if you use absolute paths unless the absolute path in filesystem and web URL is the same. See also objects/info/http-alternates. objects/info/http-alternates This file records URLs to alternate object stores that this object store borrows objects from, to be used when the repository is fetched over HTTP. refs References are stored in subdirectories of this directory. The git prune command knows to preserve objects reachable from refs found in this directory and its subdirectories. This directory is ignored (except refs/bisect, refs/rewritten and refs/worktree) if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/refs" will be used instead. refs/heads/name records tip-of-the-tree commit objects of branch name refs/tags/name records any object name (not necessarily a commit object, or a tag object that points at a commit object). refs/remotes/name records tip-of-the-tree commit objects of branches copied from a remote repository. refs/replace/<obj-sha1> records the SHA-1 of the object that replaces <obj-sha1>. This is similar to info/grafts and is internally used and maintained by git-replace(1). Such refs can be exchanged between repositories while grafts are not. packed-refs records the same information as refs/heads/, refs/tags/, and friends record in a more efficient way. See git-pack-refs(1). This file is ignored if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/packed-refs" will be used instead. HEAD A symref (see glossary) to the refs/heads/ namespace describing the currently active branch. It does not mean much if the repository is not associated with any working tree (i.e. a bare repository), but a valid Git repository must have the HEAD file; some porcelains may use it to guess the designated "default" branch of the repository (usually master). It is legal if the named branch name does not (yet) exist. In some legacy setups, it is a symbolic link instead of a symref that points at the current branch. HEAD can also record a specific commit directly, instead of being a symref to point at the current branch. Such a state is often called detached HEAD. See git-checkout(1) for details. config Repository specific configuration file. This file is ignored if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/config" will be used instead. config.worktree Working directory specific configuration file for the main working directory in multiple working directory setup (see git-worktree(1)). branches A slightly deprecated way to store shorthands to be used to specify a URL to git fetch, git pull and git push. A file can be stored as branches/<name> and then name can be given to these commands in place of repository argument. See the REMOTES section in git-fetch(1) for details. This mechanism is legacy and not likely to be found in modern repositories. This directory is ignored if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/branches" will be used instead. hooks Hooks are customization scripts used by various Git commands. A handful of sample hooks are installed when git init is run, but all of them are disabled by default. To enable, the .sample suffix has to be removed from the filename by renaming. Read githooks(5) for more details about each hook. This directory is ignored if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/hooks" will be used instead. common When multiple working trees are used, most of files in $GIT_DIR are per-worktree with a few known exceptions. All files under common however will be shared between all working trees. index The current index file for the repository. It is usually not found in a bare repository. sharedindex.<SHA-1> The shared index part, to be referenced by $GIT_DIR/index and other temporary index files. Only valid in split index mode. info Additional information about the repository is recorded in this directory. This directory is ignored if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/info" will be used instead. info/refs This file helps dumb transports discover what refs are available in this repository. If the repository is published for dumb transports, this file should be regenerated by git update-server-info every time a tag or branch is created or modified. This is normally done from the hooks/update hook, which is run by the git-receive-pack command when you git push into the repository. info/grafts This file records fake commit ancestry information, to pretend the set of parents a commit has is different from how the commit was actually created. One record per line describes a commit and its fake parents by listing their 40-byte hexadecimal object names separated by a space and terminated by a newline. Note that the grafts mechanism is outdated and can lead to problems transferring objects between repositories; see git-replace(1) for a more flexible and robust system to do the same thing. info/exclude This file, by convention among Porcelains, stores the exclude pattern list. .gitignore is the per-directory ignore file. git status, git add, git rm and git clean look at it but the core Git commands do not look at it. See also: gitignore(5). info/attributes Defines which attributes to assign to a path, similar to per-directory .gitattributes files. See also: gitattributes(5). info/sparse-checkout This file stores sparse checkout patterns. See also: git-read-tree(1). remotes Stores shorthands for URL and default refnames for use when interacting with remote repositories via git fetch, git pull and git push commands. See the REMOTES section in git-fetch(1) for details. This mechanism is legacy and not likely to be found in modern repositories. This directory is ignored if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/remotes" will be used instead. logs Records of changes made to refs are stored in this directory. See git-update-ref(1) for more information. This directory is ignored (except logs/HEAD) if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/logs" will be used instead. logs/refs/heads/name Records all changes made to the branch tip named name. logs/refs/tags/name Records all changes made to the tag named name. shallow This is similar to info/grafts but is internally used and maintained by shallow clone mechanism. See --depth option to git-clone(1) and git-fetch(1). This file is ignored if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/shallow" will be used instead. commondir If this file exists, $GIT_COMMON_DIR (see git(1)) will be set to the path specified in this file if it is not explicitly set. If the specified path is relative, it is relative to $GIT_DIR. The repository with commondir is incomplete without the repository pointed by "commondir". modules Contains the git-repositories of the submodules. worktrees Contains administrative data for linked working trees. Each subdirectory contains the working tree-related part of a linked working tree. This directory is ignored if $GIT_COMMON_DIR is set, in which case "$GIT_COMMON_DIR/worktrees" will be used instead. worktrees/<id>/gitdir A text file containing the absolute path back to the .git file that points to here. This is used to check if the linked repository has been manually removed and there is no need to keep this directory any more. The mtime of this file should be updated every time the linked repository is accessed. worktrees/<id>/locked If this file exists, the linked working tree may be on a portable device and not available. The presence of this file prevents worktrees/<id> from being pruned either automatically or manually by git worktree prune. The file may contain a string explaining why the repository is locked. worktrees/<id>/config.worktree Working directory specific configuration file.
GIT REPOSITORY FORMAT VERSIONS
Every git repository is marked with a numeric version in the core.repositoryformatversion key of its config file. This version specifies the rules for operating on the on-disk repository data. An implementation of git which does not understand a particular version advertised by an on-disk repository MUST NOT operate on that repository; doing so risks not only producing wrong results, but actually losing data. Because of this rule, version bumps should be kept to an absolute minimum. Instead, we generally prefer these strategies: • bumping format version numbers of individual data files (e.g., index, packfiles, etc). This restricts the incompatibilities only to those files. • introducing new data that gracefully degrades when used by older clients (e.g., pack bitmap files are ignored by older clients, which simply do not take advantage of the optimization they provide). A whole-repository format version bump should only be part of a change that cannot be independently versioned. For instance, if one were to change the reachability rules for objects, or the rules for locking refs, that would require a bump of the repository format version. Note that this applies only to accessing the repository’s disk contents directly. An older client which understands only format 0 may still connect via git:// to a repository using format 1, as long as the server process understands format 1. The preferred strategy for rolling out a version bump (whether whole repository or for a single file) is to teach git to read the new format, and allow writing the new format with a config switch or command line option (for experimentation or for those who do not care about backwards compatibility with older gits). Then after a long period to allow the reading capability to become common, we may switch to writing the new format by default. The currently defined format versions are: Version 0 This is the format defined by the initial version of git, including but not limited to the format of the repository directory, the repository configuration file, and the object and ref storage. Specifying the complete behavior of git is beyond the scope of this document. Version 1 This format is identical to version 0, with the following exceptions: 1. When reading the core.repositoryformatversion variable, a git implementation which supports version 1 MUST also read any configuration keys found in the extensions section of the configuration file. 2. If a version-1 repository specifies any extensions.* keys that the running git has not implemented, the operation MUST NOT proceed. Similarly, if the value of any known key is not understood by the implementation, the operation MUST NOT proceed. Note that if no extensions are specified in the config file, then core.repositoryformatversion SHOULD be set to 0 (setting it to 1 provides no benefit, and makes the repository incompatible with older implementations of git). This document will serve as the master list for extensions. Any implementation wishing to define a new extension should make a note of it here, in order to claim the name. The defined extensions are: noop This extension does not change git’s behavior at all. It is useful only for testing format-1 compatibility. preciousObjects When the config key extensions.preciousObjects is set to true, objects in the repository MUST NOT be deleted (e.g., by git-prune or git repack -d). partialclone When the config key extensions.partialclone is set, it indicates that the repo was created with a partial clone (or later performed a partial fetch) and that the remote may have omitted sending certain unwanted objects. Such a remote is called a "promisor remote" and it promises that all such omitted objects can be fetched from it in the future. The value of this key is the name of the promisor remote. worktreeConfig If set, by default "git config" reads from both "config" and "config.worktree" file from GIT_DIR in that order. In multiple working directory mode, "config" file is shared while "config.worktree" is per-working directory (i.e., it’s in GIT_COMMON_DIR/worktrees/<id>/config.worktree)
git-init(1), git-clone(1), git-fetch(1), git-pack-refs(1), git-gc(1), git-checkout(1), gitglossary(7), The Git User’s Manual
Part of the git(1) suite
1. The Git User’s Manual file:///usr/share/doc/git/html/user-manual.html