Documentation/git-push.txt: explain better cases where --force is dangerous

[git.git] / Documentation / git-push.txt

git-push(1)
===========

NAME
----
git-push - Update remote refs along with associated objects


SYNOPSIS
--------
[verse]
'git push' [--all | --mirror | --tags] [-n | --dry-run] [--receive-pack=<git-receive-pack>]
           [--repo=<repository>] [-f | --force] [--prune] [-v | --verbose] [-u | --set-upstream]
           [<repository> [<refspec>...]]

DESCRIPTION
-----------

Updates remote refs using local refs, while sending objects
necessary to complete the given refs.

You can make interesting things happen to a repository
every time you push into it, by setting up 'hooks' there.  See
documentation for linkgit:git-receive-pack[1].


OPTIONS[[OPTIONS]]
------------------
<repository>::
        The "remote" repository that is destination of a push
        operation.  This parameter can be either a URL
        (see the section <<URLS,GIT URLS>> below) or the name
        of a remote (see the section <<REMOTES,REMOTES>> below).

<refspec>...::
        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>.
        It is used to specify with what <src> object the <dst> ref
        in the remote repository is to be updated.  If not specified,
        the behavior of the command is controlled by the `push.default`
        configuration variable.
+
The <src> is often the name of the branch you would want to push, but
it can be any arbitrary "SHA-1 expression", such as `master~4` or
`HEAD` (see linkgit:gitrevisions[7]).
+
The <dst> tells which ref on the remote side is updated with this
push. Arbitrary expressions cannot be used here, an actual ref must
be named. If `:`<dst> is omitted, the same ref as <src> will be
updated.
+
The object referenced by <src> is used to update the <dst> reference
on the remote side, but by default this is only allowed if the
update can fast-forward <dst>.  By having the optional leading `+`,
you can tell git to update the <dst> ref even when the update is not a
fast-forward.  This does *not* attempt to merge <src> into <dst>.  See
EXAMPLES below for details.
+
`tag <tag>` means the same as `refs/tags/<tag>:refs/tags/<tag>`.
+
Pushing an empty <src> allows you to delete the <dst> ref from
the remote repository.
+
The special refspec `:` (or `+:` to allow non-fast-forward updates)
directs git to push "matching" branches: for every branch that exists on
the local side, the remote side is updated if a branch of the same name
already exists on the remote side.  This is the default operation mode
if no explicit refspec is found (that is neither on the command line
nor in any Push line of the corresponding remotes file---see below) and
no `push.default` configuration variable is set.

--all::
        Instead of naming each ref to push, specifies that all
        refs under `refs/heads/` be pushed.

--prune::
        Remove remote branches that don't have a local counterpart. For example
        a remote branch `tmp` will be removed if a local branch with the same
        name doesn't exist any more. This also respects refspecs, e.g.
        `git push --prune remote refs/heads/*:refs/tmp/*` would
        make sure that remote `refs/tmp/foo` will be removed if `refs/heads/foo`
        doesn't exist.

--mirror::
        Instead of naming each ref to push, specifies that all
        refs under `refs/` (which includes but is not
        limited to `refs/heads/`, `refs/remotes/`, and `refs/tags/`)
        be mirrored to the remote repository.  Newly created local
        refs will be pushed to the remote end, locally updated refs
        will be force updated on the remote end, and deleted refs
        will be removed from the remote end.  This is the default
        if the configuration option `remote.<remote>.mirror` is
        set.

-n::
--dry-run::
        Do everything except actually send the updates.

--porcelain::
        Produce machine-readable output.  The output status line for each ref
        will be tab-separated and sent to stdout instead of stderr.  The full
        symbolic names of the refs will be given.

--delete::
        All listed refs are deleted from the remote repository. This is
        the same as prefixing all refs with a colon.

--tags::
        All refs under `refs/tags` are pushed, in
        addition to refspecs explicitly listed on the command
        line.

--receive-pack=<git-receive-pack>::
--exec=<git-receive-pack>::
        Path to the 'git-receive-pack' program on the remote
        end.  Sometimes useful when pushing to a remote
        repository over ssh, and you do not have the program in
        a directory on the default $PATH.

-f::
--force::
        Usually, the command refuses to update a remote ref that is
        not an ancestor of the local ref used to overwrite it.
        This flag disables the check.  This can cause the
        remote repository to lose commits; use it with care.
        Note that `--force` applies to all the refs that are pushed,
        hence using it with `push.default` set to `matching` or with
        multiple push destinations configured with `remote.*.push`
        may overwrite refs other than the current branch (including
        local refs that are strictly behind their remote counterpart).
        To force a push to only one branch, use a `+` in front of the
        refspec to push (e.g `git push origin +master` to force a push
        to the `master` branch). See the `<refspec>...` section above
        for details.

--repo=<repository>::
        This option is only relevant if no <repository> argument is
        passed in the invocation. In this case, 'git push' derives the
        remote name from the current branch: If it tracks a remote
        branch, then that remote repository is pushed to. Otherwise,
        the name "origin" is used. For this latter case, this option
        can be used to override the name "origin". In other words,
        the difference between these two commands
+
--------------------------
git push public         #1
git push --repo=public  #2
--------------------------
+
is that #1 always pushes to "public" whereas #2 pushes to "public"
only if the current branch does not track a remote branch. This is
useful if you write an alias or script around 'git push'.

-u::
--set-upstream::
        For every branch that is up to date or successfully pushed, add
        upstream (tracking) reference, used by argument-less
        linkgit:git-pull[1] and other commands. For more information,
        see 'branch.<name>.merge' in linkgit:git-config[1].

--thin::
--no-thin::
        These options are passed to linkgit:git-send-pack[1]. A thin transfer
        significantly reduces the amount of sent data when the sender and
        receiver share many of the same objects in common. The default is
        \--thin.

-q::
--quiet::
        Suppress all output, including the listing of updated refs,
        unless an error occurs. Progress is not reported to the standard
        error stream.

-v::
--verbose::
        Run verbosely.

--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.

--recurse-submodules=check|on-demand::
        Make sure all submodule commits used by the revisions to be
        pushed are available on a remote-tracking branch. If 'check' is
        used git will verify that all submodule commits that changed in
        the revisions to be pushed are available on at least one remote
        of the submodule. If any commits are missing the push will be
        aborted and exit with non-zero status. If 'on-demand' is used
        all submodules that changed in the revisions to be pushed will
        be pushed. If on-demand was not able to push all necessary
        revisions it will also be aborted and exit with non-zero status.


include::urls-remotes.txt[]

OUTPUT
------

The output of "git push" depends on the transport method used; this
section describes the output when pushing over the git protocol (either
locally or via ssh).

The status of the push 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>)
-------------------------------

If --porcelain is used, then each line of the output is of the form:

-------------------------------
 <flag> \t <from>:<to> \t <summary> (<reason>)
-------------------------------

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

flag::
        A single character indicating the status of the ref:
(space);; for a successfully pushed fast-forward;
`+`;; for a successful forced update;
`-`;; for a successfully deleted ref;
`*`;; for a successfully pushed new ref;
`!`;; for a ref that was rejected or failed to push; and
`=`;; for a ref that was up to date and did not need pushing.

summary::
        For a successfully pushed 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).
+
For a failed update, more details are given:
+
--
rejected::
        Git did not try to send the ref at all, typically because it
        is not a fast-forward and you did not force the update.

remote rejected::
        The remote end refused the update.  Usually caused by a hook
        on the remote side, or because the remote repository has one
        of the following safety options in effect:
        `receive.denyCurrentBranch` (for pushes to the checked out
        branch), `receive.denyNonFastForwards` (for forced
        non-fast-forward updates), `receive.denyDeletes` or
        `receive.denyDeleteCurrent`.  See linkgit:git-config[1].

remote failure::
        The remote end did not report the successful update of the ref,
        perhaps because of a temporary error on the remote side, a
        break in the network connection, or other transient error.
--

from::
        The name of the local ref being pushed, minus its
        `refs/<type>/` prefix. In the case of deletion, the
        name of the local ref is omitted.

to::
        The name of the remote ref being updated, minus its
        `refs/<type>/` prefix.

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

Note about fast-forwards
------------------------

When an update changes a branch (or more in general, a ref) that used to
point at commit A to point at another commit B, it is called a
fast-forward update if and only if B is a descendant of A.

In a fast-forward update from A to B, the set of commits that the original
commit A built on top of is a subset of the commits the new commit B
builds on top of.  Hence, it does not lose any history.

In contrast, a non-fast-forward update will lose history.  For example,
suppose you and somebody else started at the same commit X, and you built
a history leading to commit B while the other person built a history
leading to commit A.  The history looks like this:

----------------

      B
     /
 ---X---A

----------------

Further suppose that the other person already pushed changes leading to A
back to the original repository from which you two obtained the original
commit X.

The push done by the other person updated the branch that used to point at
commit X to point at commit A.  It is a fast-forward.

But if you try to push, you will attempt to update the branch (that
now points at A) with commit B.  This does _not_ fast-forward.  If you did
so, the changes introduced by commit A will be lost, because everybody
will now start building on top of B.

The command by default does not allow an update that is not a fast-forward
to prevent such loss of history.

If you do not want to lose your work (history from X to B) nor the work by
the other person (history from X to A), you would need to first fetch the
history from the repository, create a history that contains changes done
by both parties, and push the result back.

You can perform "git pull", resolve potential conflicts, and "git push"
the result.  A "git pull" will create a merge commit C between commits A
and B.

----------------

      B---C
     /   /
 ---X---A

----------------

Updating A with the resulting merge commit will fast-forward and your
push will be accepted.

Alternatively, you can rebase your change between X and B on top of A,
with "git pull --rebase", and push the result back.  The rebase will
create a new commit D that builds the change between X and B on top of
A.

----------------

      B   D
     /   /
 ---X---A

----------------

Again, updating A with this commit will fast-forward and your push will be
accepted.

There is another common situation where you may encounter non-fast-forward
rejection when you try to push, and it is possible even when you are
pushing into a repository nobody else pushes into. After you push commit
A yourself (in the first picture in this section), replace it with "git
commit --amend" to produce commit B, and you try to push it out, because
forgot that you have pushed A out already. In such a case, and only if
you are certain that nobody in the meantime fetched your earlier commit A
(and started building on top of it), you can run "git push --force" to
overwrite it. In other words, "git push --force" is a method reserved for
a case where you do mean to lose history.


Examples
--------

`git push`::
        Works like `git push <remote>`, where <remote> is the
        current branch's remote (or `origin`, if no remote is
        configured for the current branch).

`git push origin`::
        Without additional configuration, works like
        `git push origin :`.
+
The default behavior of this command when no <refspec> is given can be
configured by setting the `push` option of the remote, or the `push.default`
configuration variable.
+
For example, to default to pushing only the current branch to `origin`
use `git config remote.origin.push HEAD`.  Any valid <refspec> (like
the ones in the examples below) can be configured as the default for
`git push origin`.

`git push origin :`::
        Push "matching" branches to `origin`. See
        <refspec> in the <<OPTIONS,OPTIONS>> section above for a
        description of "matching" branches.

`git push origin master`::
        Find a ref that matches `master` in the source repository
        (most likely, it would find `refs/heads/master`), and update
        the same ref (e.g. `refs/heads/master`) in `origin` repository
        with it.  If `master` did not exist remotely, it would be
        created.

`git push origin HEAD`::
        A handy way to push the current branch to the same name on the
        remote.

`git push mothership master:satellite/master dev:satellite/dev`::
        Use the source ref that matches `master` (e.g. `refs/heads/master`)
        to update the ref that matches `satellite/master` (most probably
        `refs/remotes/satellite/master`) in the `mothership` repository;
        do the same for `dev` and `satellite/dev`.
+
This is to emulate `git fetch` run on the `mothership` using `git
push` that is run in the opposite direction in order to integrate
the work done on `satellite`, and is often necessary when you can
only make connection in one way (i.e. satellite can ssh into
mothership but mothership cannot initiate connection to satellite
because the latter is behind a firewall or does not run sshd).
+
After running this `git push` on the `satellite` machine, you would
ssh into the `mothership` and run `git merge` there to complete the
emulation of `git pull` that were run on `mothership` to pull changes
made on `satellite`.

`git push origin HEAD:master`::
        Push the current branch to the remote ref matching `master` in the
        `origin` repository. This form is convenient to push the current
        branch without thinking about its local name.

`git push origin master:refs/heads/experimental`::
        Create the branch `experimental` in the `origin` repository
        by copying the current `master` branch.  This form is only
        needed to create a new branch or tag in the remote repository when
        the local name and the remote name are different; otherwise,
        the ref name on its own will work.

`git push origin :experimental`::
        Find a ref that matches `experimental` in the `origin` repository
        (e.g. `refs/heads/experimental`), and delete it.

`git push origin +dev:master`::
        Update the origin repository's master branch with the dev branch,
        allowing non-fast-forward updates.  *This can leave unreferenced
        commits dangling in the origin repository.*  Consider the
        following situation, where a fast-forward is not possible:
+
----
            o---o---o---A---B  origin/master
                     \
                      X---Y---Z  dev
----
+
The above command would change the origin repository to
+
----
                      A---B  (unnamed branch)
                     /
            o---o---o---X---Y---Z  master
----
+
Commits A and B would no longer belong to a branch with a symbolic name,
and so would be unreachable.  As such, these commits would be removed by
a `git gc` command on the origin repository.

GIT
---
Part of the linkgit:git[1] suite