fast-export: allow seeding the anonymized mapping

[thirdparty/git.git] / Documentation / git-fast-export.txt

git-fast-export(1)
==================

NAME
----
git-fast-export - Git data exporter


SYNOPSIS
--------
[verse]
'git fast-export [<options>]' | 'git fast-import'

DESCRIPTION
-----------
This program dumps the given revisions in a form suitable to be piped
into 'git fast-import'.

You can use it as a human-readable bundle replacement (see
linkgit:git-bundle[1]), or as a format that can be edited before being
fed to 'git fast-import' in order to do history rewrites (an ability
relied on by tools like 'git filter-repo').

OPTIONS
-------
--progress=<n>::
        Insert 'progress' statements every <n> objects, to be shown by
        'git fast-import' during import.

--signed-tags=(verbatim|warn|warn-strip|strip|abort)::
        Specify how to handle signed tags.  Since any transformation
        after the export can change the tag names (which can also happen
        when excluding revisions) the signatures will not match.
+
When asking to 'abort' (which is the default), this program will die
when encountering a signed tag.  With 'strip', the tags will silently
be made unsigned, with 'warn-strip' they will be made unsigned but a
warning will be displayed, with 'verbatim', they will be silently
exported and with 'warn', they will be exported, but you will see a
warning.

--tag-of-filtered-object=(abort|drop|rewrite)::
        Specify how to handle tags whose tagged object is filtered out.
        Since revisions and files to export can be limited by path,
        tagged objects may be filtered completely.
+
When asking to 'abort' (which is the default), this program will die
when encountering such a tag.  With 'drop' it will omit such tags from
the output.  With 'rewrite', if the tagged object is a commit, it will
rewrite the tag to tag an ancestor commit (via parent rewriting; see
linkgit:git-rev-list[1])

-M::
-C::
        Perform move and/or copy detection, as described in the
        linkgit:git-diff[1] manual page, and use it to generate
        rename and copy commands in the output dump.
+
Note that earlier versions of this command did not complain and
produced incorrect results if you gave these options.

--export-marks=<file>::
        Dumps the internal marks table to <file> when complete.
        Marks are written one per line as `:markid SHA-1`. Only marks
        for revisions are dumped; marks for blobs are ignored.
        Backends can use this file to validate imports after they
        have been completed, or to save the marks table across
        incremental runs.  As <file> is only opened and truncated
        at completion, the same path can also be safely given to
        --import-marks.
        The file will not be written if no new object has been
        marked/exported.

--import-marks=<file>::
        Before processing any input, load the marks specified in
        <file>.  The input file must exist, must be readable, and
        must use the same format as produced by --export-marks.

--mark-tags::
        In addition to labelling blobs and commits with mark ids, also
        label tags.  This is useful in conjunction with
        `--export-marks` and `--import-marks`, and is also useful (and
        necessary) for exporting of nested tags.  It does not hurt
        other cases and would be the default, but many fast-import
        frontends are not prepared to accept tags with mark
        identifiers.
+
Any commits (or tags) that have already been marked will not be
exported again.  If the backend uses a similar --import-marks file,
this allows for incremental bidirectional exporting of the repository
by keeping the marks the same across runs.

--fake-missing-tagger::
        Some old repositories have tags without a tagger.  The
        fast-import protocol was pretty strict about that, and did not
        allow that.  So fake a tagger to be able to fast-import the
        output.

--use-done-feature::
        Start the stream with a 'feature done' stanza, and terminate
        it with a 'done' command.

--no-data::
        Skip output of blob objects and instead refer to blobs via
        their original SHA-1 hash.  This is useful when rewriting the
        directory structure or history of a repository without
        touching the contents of individual files.  Note that the
        resulting stream can only be used by a repository which
        already contains the necessary objects.

--full-tree::
        This option will cause fast-export to issue a "deleteall"
        directive for each commit followed by a full list of all files
        in the commit (as opposed to just listing the files which are
        different from the commit's first parent).

--anonymize::
        Anonymize the contents of the repository while still retaining
        the shape of the history and stored tree.  See the section on
        `ANONYMIZING` below.

--anonymize-map=<from>[:<to>]::
        Convert token `<from>` to `<to>` in the anonymized output. If
        `<to>` is omitted, map `<from>` to itself (i.e., do not
        anonymize it). See the section on `ANONYMIZING` below.

--reference-excluded-parents::
        By default, running a command such as `git fast-export
        master~5..master` will not include the commit master{tilde}5
        and will make master{tilde}4 no longer have master{tilde}5 as
        a parent (though both the old master{tilde}4 and new
        master{tilde}4 will have all the same files).  Use
        --reference-excluded-parents to instead have the stream
        refer to commits in the excluded range of history by their
        sha1sum.  Note that the resulting stream can only be used by a
        repository which already contains the necessary parent
        commits.

--show-original-ids::
        Add an extra directive to the output for commits and blobs,
        `original-oid <SHA1SUM>`.  While such directives will likely be
        ignored by importers such as git-fast-import, it may be useful
        for intermediary filters (e.g. for rewriting commit messages
        which refer to older commits, or for stripping blobs by id).

--reencode=(yes|no|abort)::
        Specify how to handle `encoding` header in commit objects.  When
        asking to 'abort' (which is the default), this program will die
        when encountering such a commit object.  With 'yes', the commit
        message will be re-encoded into UTF-8.  With 'no', the original
        encoding will be preserved.

--refspec::
        Apply the specified refspec to each ref exported. Multiple of them can
        be specified.

[<git-rev-list-args>...]::
        A list of arguments, acceptable to 'git rev-parse' and
        'git rev-list', that specifies the specific objects and references
        to export.  For example, `master~10..master` causes the
        current master reference to be exported along with all objects
        added since its 10th ancestor commit and (unless the
        --reference-excluded-parents option is specified) all files
        common to master{tilde}9 and master{tilde}10.

EXAMPLES
--------

-------------------------------------------------------------------
$ git fast-export --all | (cd /empty/repository && git fast-import)
-------------------------------------------------------------------

This will export the whole repository and import it into the existing
empty repository.  Except for reencoding commits that are not in
UTF-8, it would be a one-to-one mirror.

-----------------------------------------------------
$ git fast-export master~5..master |
        sed "s|refs/heads/master|refs/heads/other|" |
        git fast-import
-----------------------------------------------------

This makes a new branch called 'other' from 'master~5..master'
(i.e. if 'master' has linear history, it will take the last 5 commits).

Note that this assumes that none of the blobs and commit messages
referenced by that revision range contains the string
'refs/heads/master'.


ANONYMIZING
-----------

If the `--anonymize` option is given, git will attempt to remove all
identifying information from the repository while still retaining enough
of the original tree and history patterns to reproduce some bugs. The
goal is that a git bug which is found on a private repository will
persist in the anonymized repository, and the latter can be shared with
git developers to help solve the bug.

With this option, git will replace all refnames, paths, blob contents,
commit and tag messages, names, and email addresses in the output with
anonymized data.  Two instances of the same string will be replaced
equivalently (e.g., two commits with the same author will have the same
anonymized author in the output, but bear no resemblance to the original
author string). The relationship between commits, branches, and tags is
retained, as well as the commit timestamps (but the commit messages and
refnames bear no resemblance to the originals). The relative makeup of
the tree is retained (e.g., if you have a root tree with 10 files and 3
trees, so will the output), but their names and the contents of the
files will be replaced.

If you think you have found a git bug, you can start by exporting an
anonymized stream of the whole repository:

---------------------------------------------------
$ git fast-export --anonymize --all >anon-stream
---------------------------------------------------

Then confirm that the bug persists in a repository created from that
stream (many bugs will not, as they really do depend on the exact
repository contents):

---------------------------------------------------
$ git init anon-repo
$ cd anon-repo
$ git fast-import <../anon-stream
$ ... test your bug ...
---------------------------------------------------

If the anonymized repository shows the bug, it may be worth sharing
`anon-stream` along with a regular bug report. Note that the anonymized
stream compresses very well, so gzipping it is encouraged. If you want
to examine the stream to see that it does not contain any private data,
you can peruse it directly before sending. You may also want to try:

---------------------------------------------------
$ perl -pe 's/\d+/X/g' <anon-stream | sort -u | less
---------------------------------------------------

which shows all of the unique lines (with numbers converted to "X", to
collapse "User 0", "User 1", etc into "User X"). This produces a much
smaller output, and it is usually easy to quickly confirm that there is
no private data in the stream.

Reproducing some bugs may require referencing particular commits or
paths, which becomes challenging after refnames and paths have been
anonymized. You can ask for a particular token to be left as-is or
mapped to a new value. For example, if you have a bug which reproduces
with `git rev-list sensitive -- secret.c`, you can run:

---------------------------------------------------
$ git fast-export --anonymize --all \
      --anonymize-map=sensitive:foo \
      --anonymize-map=secret.c:bar.c \
      >stream
---------------------------------------------------

After importing the stream, you can then run `git rev-list foo -- bar.c`
in the anonymized repository.

Note that paths and refnames are split into tokens at slash boundaries.
The command above would anonymize `subdir/secret.c` as something like
`path123/bar.c`; you could then search for `bar.c` in the anonymized
repository to determine the final pathname.

To make referencing the final pathname simpler, you can map each path
component; so if you also anonymize `subdir` to `publicdir`, then the
final pathname would be `publicdir/bar.c`.

LIMITATIONS
-----------

Since 'git fast-import' cannot tag trees, you will not be
able to export the linux.git repository completely, as it contains
a tag referencing a tree instead of a commit.

SEE ALSO
--------
linkgit:git-fast-import[1]

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