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git-fetch (draft)

NAME

git-fetch - Download objects and refs from another repository

SYNOPSIS

git fetch [<options>] [<repository> [<refspec>...]]
git fetch [<options>] <group>
git fetch --multiple [<options>] [(<repository> | <group>)...]
git fetch --all [<options>]

DESCRIPTION

Fetch branches and/or tags (collectively, “refs”) from one or more other repositories, along with the objects necessary to complete their histories. Remote-tracking branches are updated (see the description of <refspec> below for ways to control this behavior).

By default, any tag that points into the histories being fetched is also fetched; the effect is to fetch tags that point at branches that you are interested in. This default behavior can be changed by using the –tags or –no-tags options or by configuring remote.<name>.tagOpt. By using a refspec that fetches tags explicitly, you can fetch tags that do not point into branches you are interested in as well.

git fetch can fetch from either a single named repository or URL, or from several repositories at once if <group> is given and there is a remotes.<group> entry in the configuration file. (See linkgit:git-config[1]).

When no remote is specified, by default the origin remote will be used, unless there’s an upstream branch configured for the current branch.

The names of refs that are fetched, together with the object names they point at, are written to .git/FETCH_HEAD. This information may be used by scripts or other git commands, such as linkgit:git-pull[1].

OPTIONS

--all

Fetch all remotes.

-a; --append

Append ref names and object names of fetched refs to the existing contents of .git/FETCH_HEAD. Without this option old data in .git/FETCH_HEAD will be overwritten.

--depth=<depth>

Limit fetching to the specified number of commits from the tip of each remote branch history. If fetching to a shallow repository created by git clone with --depth=<depth> option (see linkgit:git-clone[1]), deepen or shorten the history to the specified number of commits. Tags for the deepened commits are not fetched.

--deepen=<depth>

Similar to –depth, except it specifies the number of commits from the current shallow boundary instead of from the tip of each remote branch history.

--shallow-since=<date>

Deepen or shorten the history of a shallow repository to include all reachable commits after <date>.

--shallow-exclude=<revision>

Deepen or shorten the history of a shallow repository to exclude commits reachable from a specified remote branch or tag. This option can be specified multiple times.

--unshallow

If the source repository is complete, convert a shallow repository to a complete one, removing all the limitations imposed by shallow repositories.

If the source repository is shallow, fetch as much as possible so that the current repository has the same history as the source repository.

--update-shallow

By default when fetching from a shallow repository, git fetch refuses refs that require updating .git/shallow. This option updates .git/shallow and accept such refs.

--dry-run

Show what would be done, without making any changes.

-f; --force

When git fetch is used with <rbranch>:<lbranch> refspec, it refuses to update the local branch <lbranch> unless the remote branch <rbranch> it fetches is a descendant of <lbranch>. This option overrides that check.

-k; --keep

Keep downloaded pack.

--multiple

Allow several <repository> and <group> arguments to be specified. No <refspec>s may be specified.

-p; --prune

Before fetching, remove any remote-tracking references that no longer exist on the remote. Tags are not subject to pruning if they are fetched only because of the default tag auto-following or due to a –tags option. However, if tags are fetched due to an explicit refspec (either on the command line or in the remote configuration, for example if the remote was cloned with the –mirror option), then they are also subject to pruning.

-n; --no-tags

By default, tags that point at objects that are downloaded from the remote repository are fetched and stored locally. This option disables this automatic tag following. The default behavior for a remote may be specified with the remote.<name>.tagOpt setting. See linkgit:git-config[1].

--refmap=<refspec>

When fetching refs listed on the command line, use the specified refspec (can be given more than once) to map the refs to remote-tracking branches, instead of the values of remote.*.fetch configuration variables for the remote repository. See section on “Configured Remote-tracking Branches” for details.

-t; --tags

Fetch all tags from the remote (i.e., fetch remote tags refs/tags/* into local tags with the same name), in addition to whatever else would otherwise be fetched. Using this option alone does not subject tags to pruning, even if –prune is used (though tags may be pruned anyway if they are also the destination of an explicit refspec; see --prune).

--recurse-submodules[=yes|on-demand|no]

This option controls if and under what conditions new commits of populated submodules should be fetched too. It can be used as a boolean option to completely disable recursion when set to no or to unconditionally recurse into all populated submodules when set to yes, which is the default when this option is used without any value. Use on-demand to only recurse into a populated submodule when the superproject retrieves a commit that updates the submodule’s reference to a commit that isn’t already in the local submodule clone.

-j; --jobs=<n>

Number of parallel children to be used for fetching submodules. Each will fetch from different submodules, such that fetching many submodules will be faster. By default submodules will be fetched one at a time.

--no-recurse-submodules

Disable recursive fetching of submodules (this has the same effect as using the --recurse-submodules=no option).

--submodule-prefix=<path>

Prepend <path> to paths printed in informative messages such as “Fetching submodule foo”. This option is used internally when recursing over submodules.

--recurse-submodules-default=[yes|on-demand]

This option is used internally to temporarily provide a non-negative default value for the –recurse-submodules option. All other methods of configuring fetch’s submodule recursion (such as settings in linkgit:gitmodules[5] and linkgit:git-config[1]) override this option, as does specifying –[no-]recurse-submodules directly.

-u; --update-head-ok

By default git fetch refuses to update the head which corresponds to the current branch. This flag disables the check. This is purely for the internal use for git pull to communicate with git fetch, and unless you are implementing your own Porcelain you are not supposed to use it.

--upload-pack <upload-pack>

When given, and the repository to fetch from is handled by git fetch-pack, --exec=<upload-pack> is passed to the command to specify non-default path for the command run on the other end.

-q; --quiet

Pass –quiet to git-fetch-pack and silence any other internally used git commands. Progress is not reported to the standard error stream.

-v; --verbose

Be verbose.

--progress

Progress status is reported on the standard error stream by default when it is attached to a terminal, unless -q is specified. This flag forces progress status even if the standard error stream is not directed to a terminal.

-4; --ipv4

Use IPv4 addresses only, ignoring IPv6 addresses.

-6; --ipv6

Use IPv6 addresses only, ignoring IPv4 addresses.

<repository>

The “remote” repository that is the source of a fetch or pull operation. This parameter can be either a URL (see the section GIT URLS below) or the name of a remote (see the section REMOTES below).

<group>

A name referring to a list of repositories as the value of remotes.<group> in the configuration file. (See linkgit:git-config[1]).

<refspec>

Specifies which refs to fetch and which local refs to update. When no <refspec>s appear on the command line, the refs to fetch are read from remote.<repository>.fetch variables instead (see CONFIGURED REMOTE-TRACKING BRANCHES below).

The format of a <refspec> parameter is an optional plus +, followed by the source ref <src>, followed by a colon :, followed by the destination ref <dst>. The colon can be omitted when <dst> is empty.

tag <tag> means the same as refs/tags/<tag>:refs/tags/<tag>; it requests fetching everything up to the given tag.

The remote ref that matches <src> is fetched, and if <dst> is not empty string, the local ref that matches it is fast-forwarded using <src>. If the optional plus + is used, the local ref is updated even if it does not result in a fast-forward update.

Note

When the remote branch you want to fetch is known to be rewound and rebased regularly, it is expected that its new tip will not be descendant of its previous tip (as stored in your remote-tracking branch the last time you fetched). You would want to use the + sign to indicate non-fast-forward updates will be needed for such branches. There is no way to determine or declare that a branch will be made available in a repository with this behavior; the pulling user simply must know this is the expected usage pattern for a branch.

GIT URLS

In general, URLs contain information about the transport protocol, the address of the remote server, and the path to the repository. Depending on the transport protocol, some of this information may be absent.

Git supports ssh, git, http, and https protocols (in addition, ftp, and ftps can be used for fetching, but this is inefficient and deprecated; do not use it).

The native transport (i.e. git:// URL) does no authentication and should be used with caution on unsecured networks.

The following syntaxes may be used with them:

An alternative scp-like syntax may also be used with the ssh protocol:

This syntax is only recognized if there are no slashes before the first colon. This helps differentiate a local path that contains a colon. For example the local path foo:bar could be specified as an absolute path or ./foo:bar to avoid being misinterpreted as an ssh url.

The ssh and git protocols additionally support ~username expansion:

For local repositories, also supported by Git natively, the following syntaxes may be used:

• /path/to/repo.git/

• file:///path/to/repo.git/

These two syntaxes are mostly equivalent, except when cloning, when the former implies –local option. See linkgit:git-clone[1] for details.

When Git doesn’t know how to handle a certain transport protocol, it attempts to use the remote-<transport> remote helper, if one exists. To explicitly request a remote helper, the following syntax may be used:

• <transport>::<address>

where <address> may be a path, a server and path, or an arbitrary URL-like string recognized by the specific remote helper being invoked. See linkgit:gitremote-helpers[1] for details.

If there are a large number of similarly-named remote repositories and you want to use a different format for them (such that the URLs you use will be rewritten into URLs that work), you can create a configuration section of the form:

        [url "<actual url base>"]
                insteadOf = <other url base>

For example, with this:

        [url "git://git.host.xz/"]
                insteadOf = host.xz:/path/to/
                insteadOf = work:

a URL like “work:repo.git” or like “host.xz:/path/to/repo.git” will be rewritten in any context that takes a URL to be “git://git.host.xz/repo.git”.

If you want to rewrite URLs for push only, you can create a configuration section of the form:

        [url "<actual url base>"]
                pushInsteadOf = <other url base>

For example, with this:

        [url "ssh://example.org/"]
                pushInsteadOf = git://example.org/

a URL like “git://example.org/path/to/repo.git” will be rewritten to “ssh://example.org/path/to/repo.git” for pushes, but pulls will still use the original URL.

REMOTES

The name of one of the following can be used instead of a URL as <repository> argument:

• a remote in the Git configuration file: $GIT_DIR/config,

• a file in the $GIT_DIR/remotes directory, or

• a file in the $GIT_DIR/branches directory.

All of these also allow you to omit the refspec from the command line because they each contain a refspec which git will use by default.

Named remote in configuration file

You can choose to provide the name of a remote which you had previously configured using linkgit:git-remote[1], linkgit:git-config[1] or even by a manual edit to the $GIT_DIR/config file. The URL of this remote will be used to access the repository. The refspec of this remote will be used by default when you do not provide a refspec on the command line. The entry in the config file would appear like this:

        [remote "<name>"]
                url = <url>
                pushurl = <pushurl>
                push = <refspec>
                fetch = <refspec>

The <pushurl> is used for pushes only. It is optional and defaults to <url>.

Named file in $GIT_DIR/remotes

You can choose to provide the name of a file in $GIT_DIR/remotes. The URL in this file will be used to access the repository. The refspec in this file will be used as default when you do not provide a refspec on the command line. This file should have the following format:

        URL: one of the above URL format
        Push: <refspec>
        Pull: <refspec>

Push: lines are used by git push and Pull: lines are used by git pull and git fetch. Multiple Push: and Pull: lines may be specified for additional branch mappings.

Named file in $GIT_DIR/branches

You can choose to provide the name of a file in $GIT_DIR/branches. The URL in this file will be used to access the repository. This file should have the following format:

        <url>#<head>

<url> is required; #<head> is optional.

Depending on the operation, git will use one of the following refspecs, if you don’t provide one on the command line. <branch> is the name of this file in $GIT_DIR/branches and <head> defaults to master.

git fetch uses:

        refs/heads/<head>:refs/heads/<branch>

git push uses:

        HEAD:refs/heads/<head>

CONFIGURED REMOTE-TRACKING BRANCHES

You often interact with the same remote repository by regularly and repeatedly fetching from it. In order to keep track of the progress of such a remote repository, git fetch allows you to configure remote.<repository>.fetch configuration variables.

Typically such a variable may look like this:

[remote "origin"]
        fetch = +refs/heads/*:refs/remotes/origin/*

This configuration is used in two ways:

• When git fetch is run without specifying what branches and/or tags to fetch on the command line, e.g. git fetch origin or git fetch, remote.<repository>.fetch values are used as the refspecs—they specify which refs to fetch and which local refs to update. The example above will fetch all branches that exist in the origin (i.e. any ref that matches the left-hand side of the value, refs/heads/*) and update the corresponding remote-tracking branches in the refs/remotes/origin/* hierarchy.

• When git fetch is run with explicit branches and/or tags to fetch on the command line, e.g. git fetch origin master, the <refspec>s given on the command line determine what are to be fetched (e.g. master in the example, which is a short-hand for master:, which in turn means “fetch the master branch but I do not explicitly say what remote-tracking branch to update with it from the command line”), and the example command will fetch only the master branch. The remote.<repository>.fetch values determine which remote-tracking branch, if any, is updated. When used in this way, the remote.<repository>.fetch values do not have any effect in deciding what gets fetched (i.e. the values are not used as refspecs when the command-line lists refspecs); they are only used to decide where the refs that are fetched are stored by acting as a mapping.

The latter use of the remote.<repository>.fetch values can be overridden by giving the --refmap=<refspec> parameter(s) on the command line.

OUTPUT

The output of “git fetch” depends on the transport method used; this section describes the output when fetching over the Git protocol (either locally or via ssh) and Smart HTTP protocol.

The status of the fetch is output in tabular form, with each line representing the status of a single ref. Each line is of the form:

 <flag> <summary> <from> -> <to> [<reason>]

The status of up-to-date refs is shown only if the –verbose option is used.

In compact output mode, specified with configuration variable fetch.output, if either entire <from> or <to> is found in the other string, it will be substituted with * in the other string. For example, master -> origin/master becomes master -> origin/*.

flag

A single character indicating the status of the ref:

(space)

for a successfully fetched fast-forward;

+

for a successful forced update;

-

for a successfully pruned ref;

t

for a successful tag update;

*

for a successfully fetched new ref;

!

for a ref that was rejected or failed to update; and

=

for a ref that was up to date and did not need fetching.

summary

For a successfully fetched ref, the summary shows the old and new values of the ref in a form suitable for using as an argument to git log (this is <old>..<new> in most cases, and <old>...<new> for forced non-fast-forward updates).

from

The name of the remote ref being fetched from, minus its refs/<type>/ prefix. In the case of deletion, the name of the remote ref is “(none)”.

to

The name of the local ref being updated, minus its refs/<type>/ prefix.

reason

A human-readable explanation. In the case of successfully fetched refs, no explanation is needed. For a failed ref, the reason for failure is described.

EXAMPLES

• Update the remote-tracking branches:

  $ git fetch origin
  

  The above command copies all branches from the remote refs/heads/ namespace and stores them to the local refs/remotes/origin/ namespace, unless the branch.<name>.fetch option is used to specify a non-default refspec.

• Using refspecs explicitly:

  $ git fetch origin +pu:pu maint:tmp
  

  This updates (or creates, as necessary) branches pu and tmp in the local repository by fetching from the branches (respectively) pu and maint from the remote repository.

  The pu branch will be updated even if it is does not fast-forward, because it is prefixed with a plus sign; tmp will not be.

• Peek at a remote’s branch, without configuring the remote in your local repository:

  $ git fetch git://git.kernel.org/pub/scm/git/git.git maint
  $ git log FETCH_HEAD
  

  The first command fetches the maint branch from the repository at git://git.kernel.org/pub/scm/git/git.git and the second command uses FETCH_HEAD to examine the branch with linkgit:git-log[1]. The fetched objects will eventually be removed by git’s built-in housekeeping (see linkgit:git-gc[1]).

SECURITY

The fetch and push protocols are not designed to prevent one side from stealing data from the other repository that was not intended to be shared. If you have private data that you need to protect from a malicious peer, your best option is to store it in another repository. This applies to both clients and servers. In particular, namespaces on a server are not effective for read access control; you should only grant read access to a namespace to clients that you would trust with read access to the entire repository.

The known attack vectors are as follows:

1. The victim sends “have” lines advertising the IDs of objects it has that are not explicitly intended to be shared but can be used to optimize the transfer if the peer also has them. The attacker chooses an object ID X to steal and sends a ref to X, but isn’t required to send the content of X because the victim already has it. Now the victim believes that the attacker has X, and it sends the content of X back to the attacker later. (This attack is most straightforward for a client to perform on a server, by creating a ref to X in the namespace the client has access to and then fetching it. The most likely way for a server to perform it on a client is to “merge” X into a public branch and hope that the user does additional work on this branch and pushes it back to the server without noticing the merge.)

2. As in #1, the attacker chooses an object ID X to steal. The victim sends an object Y that the attacker already has, and the attacker falsely claims to have X and not Y, so the victim sends Y as a delta against X. The delta reveals regions of X that are similar to Y to the attacker.

BUGS

Using –recurse-submodules can only fetch new commits in already checked out submodules right now. When e.g. upstream added a new submodule in the just fetched commits of the superproject the submodule itself can not be fetched, making it impossible to check out that submodule later without having to do a fetch again. This is expected to be fixed in a future Git version.

SEE ALSO

linkgit:git-pull[1]

GIT

Part of the linkgit:git[1] suite