git-fast-import(1)



GIT-FAST-IMPORT(1)                Git Manual                GIT-FAST-IMPORT(1)

NAME
       git-fast-import - Backend for fast Git data importers

SYNOPSIS
       frontend | git fast-import [options]

DESCRIPTION
       This program is usually not what the end user wants to run directly.
       Most end users want to use one of the existing frontend programs, which
       parses a specific type of foreign source and feeds the contents stored
       there to git fast-import.

       fast-import reads a mixed command/data stream from standard input and
       writes one or more packfiles directly into the current repository. When
       EOF is received on standard input, fast import writes out updated
       branch and tag refs, fully updating the current repository with the
       newly imported data.

       The fast-import backend itself can import into an empty repository (one
       that has already been initialized by git init) or incrementally update
       an existing populated repository. Whether or not incremental imports
       are supported from a particular foreign source depends on the frontend
       program in use.

OPTIONS
       --force
           Force updating modified existing branches, even if doing so would
           cause commits to be lost (as the new commit does not contain the
           old commit).

       --quiet
           Disable all non-fatal output, making fast-import silent when it is
           successful. This option disables the output shown by --stats.

       --stats
           Display some basic statistics about the objects fast-import has
           created, the packfiles they were stored into, and the memory used
           by fast-import during this run. Showing this output is currently
           the default, but can be disabled with --quiet.

   Options for Frontends
       --cat-blob-fd=<fd>
           Write responses to get-mark, cat-blob, and ls queries to the file
           descriptor <fd> instead of stdout. Allows progress output intended
           for the end-user to be separated from other output.

       --date-format=<fmt>
           Specify the type of dates the frontend will supply to fast-import
           within author, committer and tagger commands. See "Date Formats"
           below for details about which formats are supported, and their
           syntax.

       --done
           Terminate with error if there is no done command at the end of the
           stream. This option might be useful for detecting errors that cause
           the frontend to terminate before it has started to write a stream.

   Locations of Marks Files
       --export-marks=<file>
           Dumps the internal marks table to <file> when complete. Marks are
           written one per line as :markid SHA-1. Frontends 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 checkpoint (or completion) the same path can also be
           safely given to --import-marks.

       --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. Multiple options may be
           supplied to import more than one set of marks. If a mark is defined
           to different values, the last file wins.

       --import-marks-if-exists=<file>
           Like --import-marks but instead of erroring out, silently skips the
           file if it does not exist.

       --[no-]relative-marks
           After specifying --relative-marks the paths specified with
           --import-marks= and --export-marks= are relative to an internal
           directory in the current repository. In git-fast-import this means
           that the paths are relative to the .git/info/fast-import directory.
           However, other importers may use a different location.

           Relative and non-relative marks may be combined by interweaving
           --(no-)-relative-marks with the --(import|export)-marks= options.

   Performance and Compression Tuning
       --active-branches=<n>
           Maximum number of branches to maintain active at once. See "Memory
           Utilization" below for details. Default is 5.

       --big-file-threshold=<n>
           Maximum size of a blob that fast-import will attempt to create a
           delta for, expressed in bytes. The default is 512m (512 MiB). Some
           importers may wish to lower this on systems with constrained
           memory.

       --depth=<n>
           Maximum delta depth, for blob and tree deltification. Default is
           50.

       --export-pack-edges=<file>
           After creating a packfile, print a line of data to <file> listing
           the filename of the packfile and the last commit on each branch
           that was written to that packfile. This information may be useful
           after importing projects whose total object set exceeds the 4 GiB
           packfile limit, as these commits can be used as edge points during
           calls to git pack-objects.

       --max-pack-size=<n>
           Maximum size of each output packfile. The default is unlimited.

       fastimport.unpackLimit
           See git-config(1)

PERFORMANCE
       The design of fast-import allows it to import large projects in a
       minimum amount of memory usage and processing time. Assuming the
       frontend is able to keep up with fast-import and feed it a constant
       stream of data, import times for projects holding 10+ years of history
       and containing 100,000+ individual commits are generally completed in
       just 1-2 hours on quite modest (~$2,000 USD) hardware.

       Most bottlenecks appear to be in foreign source data access (the source
       just cannot extract revisions fast enough) or disk IO (fast-import
       writes as fast as the disk will take the data). Imports will run faster
       if the source data is stored on a different drive than the destination
       Git repository (due to less IO contention).

DEVELOPMENT COST
       A typical frontend for fast-import tends to weigh in at approximately
       200 lines of Perl/Python/Ruby code. Most developers have been able to
       create working importers in just a couple of hours, even though it is
       their first exposure to fast-import, and sometimes even to Git. This is
       an ideal situation, given that most conversion tools are throw-away
       (use once, and never look back).

PARALLEL OPERATION
       Like git push or git fetch, imports handled by fast-import are safe to
       run alongside parallel git repack -a -d or git gc invocations, or any
       other Git operation (including git prune, as loose objects are never
       used by fast-import).

       fast-import does not lock the branch or tag refs it is actively
       importing. After the import, during its ref update phase, fast-import
       tests each existing branch ref to verify the update will be a
       fast-forward update (the commit stored in the ref is contained in the
       new history of the commit to be written). If the update is not a
       fast-forward update, fast-import will skip updating that ref and
       instead prints a warning message. fast-import will always attempt to
       update all branch refs, and does not stop on the first failure.

       Branch updates can be forced with --force, but it's recommended that
       this only be used on an otherwise quiet repository. Using --force is
       not necessary for an initial import into an empty repository.

TECHNICAL DISCUSSION
       fast-import tracks a set of branches in memory. Any branch can be
       created or modified at any point during the import process by sending a
       commit command on the input stream. This design allows a frontend
       program to process an unlimited number of branches simultaneously,
       generating commits in the order they are available from the source
       data. It also simplifies the frontend programs considerably.

       fast-import does not use or alter the current working directory, or any
       file within it. (It does however update the current Git repository, as
       referenced by GIT_DIR.) Therefore an import frontend may use the
       working directory for its own purposes, such as extracting file
       revisions from the foreign source. This ignorance of the working
       directory also allows fast-import to run very quickly, as it does not
       need to perform any costly file update operations when switching
       between branches.

INPUT FORMAT
       With the exception of raw file data (which Git does not interpret) the
       fast-import input format is text (ASCII) based. This text based format
       simplifies development and debugging of frontend programs, especially
       when a higher level language such as Perl, Python or Ruby is being
       used.

       fast-import is very strict about its input. Where we say SP below we
       mean exactly one space. Likewise LF means one (and only one) linefeed
       and HT one (and only one) horizontal tab. Supplying additional
       whitespace characters will cause unexpected results, such as branch
       names or file names with leading or trailing spaces in their name, or
       early termination of fast-import when it encounters unexpected input.

   Stream Comments
       To aid in debugging frontends fast-import ignores any line that begins
       with # (ASCII pound/hash) up to and including the line ending LF. A
       comment line may contain any sequence of bytes that does not contain an
       LF and therefore may be used to include any detailed debugging
       information that might be specific to the frontend and useful when
       inspecting a fast-import data stream.

   Date Formats
       The following date formats are supported. A frontend should select the
       format it will use for this import by passing the format name in the
       --date-format=<fmt> command-line option.

       raw
           This is the Git native format and is <time> SP <offutc>. It is also
           fast-import's default format, if --date-format was not specified.

           The time of the event is specified by <time> as the number of
           seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is
           written as an ASCII decimal integer.

           The local offset is specified by <offutc> as a positive or negative
           offset from UTC. For example EST (which is 5 hours behind UTC)
           would be expressed in <tz> by "-0500" while UTC is "+0000". The
           local offset does not affect <time>; it is used only as an
           advisement to help formatting routines display the timestamp.

           If the local offset is not available in the source material, use
           "+0000", or the most common local offset. For example many
           organizations have a CVS repository which has only ever been
           accessed by users who are located in the same location and time
           zone. In this case a reasonable offset from UTC could be assumed.

           Unlike the rfc2822 format, this format is very strict. Any
           variation in formatting will cause fast-import to reject the value.

       rfc2822
           This is the standard email format as described by RFC 2822.

           An example value is "Tue Feb 6 11:22:18 2007 -0500". The Git parser
           is accurate, but a little on the lenient side. It is the same
           parser used by git am when applying patches received from email.

           Some malformed strings may be accepted as valid dates. In some of
           these cases Git will still be able to obtain the correct date from
           the malformed string. There are also some types of malformed
           strings which Git will parse wrong, and yet consider valid.
           Seriously malformed strings will be rejected.

           Unlike the raw format above, the time zone/UTC offset information
           contained in an RFC 2822 date string is used to adjust the date
           value to UTC prior to storage. Therefore it is important that this
           information be as accurate as possible.

           If the source material uses RFC 2822 style dates, the frontend
           should let fast-import handle the parsing and conversion (rather
           than attempting to do it itself) as the Git parser has been well
           tested in the wild.

           Frontends should prefer the raw format if the source material
           already uses UNIX-epoch format, can be coaxed to give dates in that
           format, or its format is easily convertible to it, as there is no
           ambiguity in parsing.

       now
           Always use the current time and time zone. The literal now must
           always be supplied for <when>.

           This is a toy format. The current time and time zone of this system
           is always copied into the identity string at the time it is being
           created by fast-import. There is no way to specify a different time
           or time zone.

           This particular format is supplied as it's short to implement and
           may be useful to a process that wants to create a new commit right
           now, without needing to use a working directory or git
           update-index.

           If separate author and committer commands are used in a commit the
           timestamps may not match, as the system clock will be polled twice
           (once for each command). The only way to ensure that both author
           and committer identity information has the same timestamp is to
           omit author (thus copying from committer) or to use a date format
           other than now.

   Commands
       fast-import accepts several commands to update the current repository
       and control the current import process. More detailed discussion (with
       examples) of each command follows later.

       commit
           Creates a new branch or updates an existing branch by creating a
           new commit and updating the branch to point at the newly created
           commit.

       tag
           Creates an annotated tag object from an existing commit or branch.
           Lightweight tags are not supported by this command, as they are not
           recommended for recording meaningful points in time.

       reset
           Reset an existing branch (or a new branch) to a specific revision.
           This command must be used to change a branch to a specific revision
           without making a commit on it.

       blob
           Convert raw file data into a blob, for future use in a commit
           command. This command is optional and is not needed to perform an
           import.

       checkpoint
           Forces fast-import to close the current packfile, generate its
           unique SHA-1 checksum and index, and start a new packfile. This
           command is optional and is not needed to perform an import.

       progress
           Causes fast-import to echo the entire line to its own standard
           output. This command is optional and is not needed to perform an
           import.

       done
           Marks the end of the stream. This command is optional unless the
           done feature was requested using the --done command-line option or
           feature done command.

       get-mark
           Causes fast-import to print the SHA-1 corresponding to a mark to
           the file descriptor set with --cat-blob-fd, or stdout if
           unspecified.

       cat-blob
           Causes fast-import to print a blob in cat-file --batch format to
           the file descriptor set with --cat-blob-fd or stdout if
           unspecified.

       ls
           Causes fast-import to print a line describing a directory entry in
           ls-tree format to the file descriptor set with --cat-blob-fd or
           stdout if unspecified.

       feature
           Enable the specified feature. This requires that fast-import
           supports the specified feature, and aborts if it does not.

       option
           Specify any of the options listed under OPTIONS that do not change
           stream semantic to suit the frontend's needs. This command is
           optional and is not needed to perform an import.

   commit
       Create or update a branch with a new commit, recording one logical
       change to the project.

                   'commit' SP <ref> LF
                   mark?
                   ('author' (SP <name>)? SP LT <email> GT SP <when> LF)?
                   'committer' (SP <name>)? SP LT <email> GT SP <when> LF
                   data
                   ('from' SP <commit-ish> LF)?
                   ('merge' SP <commit-ish> LF)?
                   (filemodify | filedelete | filecopy | filerename | filedeleteall | notemodify)*
                   LF?

       where <ref> is the name of the branch to make the commit on. Typically
       branch names are prefixed with refs/heads/ in Git, so importing the CVS
       branch symbol RELENG-1_0 would use refs/heads/RELENG-1_0 for the value
       of <ref>. The value of <ref> must be a valid refname in Git. As LF is
       not valid in a Git refname, no quoting or escaping syntax is supported
       here.

       A mark command may optionally appear, requesting fast-import to save a
       reference to the newly created commit for future use by the frontend
       (see below for format). It is very common for frontends to mark every
       commit they create, thereby allowing future branch creation from any
       imported commit.

       The data command following committer must supply the commit message
       (see below for data command syntax). To import an empty commit message
       use a 0 length data. Commit messages are free-form and are not
       interpreted by Git. Currently they must be encoded in UTF-8, as
       fast-import does not permit other encodings to be specified.

       Zero or more filemodify, filedelete, filecopy, filerename,
       filedeleteall and notemodify commands may be included to update the
       contents of the branch prior to creating the commit. These commands may
       be supplied in any order. However it is recommended that a
       filedeleteall command precede all filemodify, filecopy, filerename and
       notemodify commands in the same commit, as filedeleteall wipes the
       branch clean (see below).

       The LF after the command is optional (it used to be required).

       author
           An author command may optionally appear, if the author information
           might differ from the committer information. If author is omitted
           then fast-import will automatically use the committer's information
           for the author portion of the commit. See below for a description
           of the fields in author, as they are identical to committer.

       committer
           The committer command indicates who made this commit, and when they
           made it.

           Here <name> is the person's display name (for example "Com M
           Itter") and <email> is the person's email address
           ("cm@example.com"). LT and GT are the literal less-than (\x3c) and
           greater-than (\x3e) symbols. These are required to delimit the
           email address from the other fields in the line. Note that <name>
           and <email> are free-form and may contain any sequence of bytes,
           except LT, GT and LF. <name> is typically UTF-8 encoded.

           The time of the change is specified by <when> using the date format
           that was selected by the --date-format=<fmt> command-line option.
           See "Date Formats" above for the set of supported formats, and
           their syntax.

       from
           The from command is used to specify the commit to initialize this
           branch from. This revision will be the first ancestor of the new
           commit. The state of the tree built at this commit will begin with
           the state at the from commit, and be altered by the content
           modifications in this commit.

           Omitting the from command in the first commit of a new branch will
           cause fast-import to create that commit with no ancestor. This
           tends to be desired only for the initial commit of a project. If
           the frontend creates all files from scratch when making a new
           branch, a merge command may be used instead of from to start the
           commit with an empty tree. Omitting the from command on existing
           branches is usually desired, as the current commit on that branch
           is automatically assumed to be the first ancestor of the new
           commit.

           As LF is not valid in a Git refname or SHA-1 expression, no quoting
           or escaping syntax is supported within <commit-ish>.

           Here <commit-ish> is any of the following:

           o   The name of an existing branch already in fast-import's
               internal branch table. If fast-import doesn't know the name,
               it's treated as a SHA-1 expression.

           o   A mark reference, :<idnum>, where <idnum> is the mark number.

               The reason fast-import uses : to denote a mark reference is
               this character is not legal in a Git branch name. The leading :
               makes it easy to distinguish between the mark 42 (:42) and the
               branch 42 (42 or refs/heads/42), or an abbreviated SHA-1 which
               happened to consist only of base-10 digits.

               Marks must be declared (via mark) before they can be used.

           o   A complete 40 byte or abbreviated commit SHA-1 in hex.

           o   Any valid Git SHA-1 expression that resolves to a commit. See
               "SPECIFYING REVISIONS" in gitrevisions(7) for details.

           o   The special null SHA-1 (40 zeros) specifies that the branch is
               to be removed.

           The special case of restarting an incremental import from the
           current branch value should be written as:

                       from refs/heads/branch^0

           The ^0 suffix is necessary as fast-import does not permit a branch
           to start from itself, and the branch is created in memory before
           the from command is even read from the input. Adding ^0 will force
           fast-import to resolve the commit through Git's revision parsing
           library, rather than its internal branch table, thereby loading in
           the existing value of the branch.

       merge
           Includes one additional ancestor commit. The additional ancestry
           link does not change the way the tree state is built at this
           commit. If the from command is omitted when creating a new branch,
           the first merge commit will be the first ancestor of the current
           commit, and the branch will start out with no files. An unlimited
           number of merge commands per commit are permitted by fast-import,
           thereby establishing an n-way merge.

           Here <commit-ish> is any of the commit specification expressions
           also accepted by from (see above).

       filemodify
           Included in a commit command to add a new file or change the
           content of an existing file. This command has two different means
           of specifying the content of the file.

           External data format
               The data content for the file was already supplied by a prior
               blob command. The frontend just needs to connect it.

                           'M' SP <mode> SP <dataref> SP <path> LF

               Here usually <dataref> must be either a mark reference
               (:<idnum>) set by a prior blob command, or a full 40-byte SHA-1
               of an existing Git blob object. If <mode> is 040000` then
               <dataref> must be the full 40-byte SHA-1 of an existing Git
               tree object or a mark reference set with --import-marks.

           Inline data format
               The data content for the file has not been supplied yet. The
               frontend wants to supply it as part of this modify command.

                           'M' SP <mode> SP 'inline' SP <path> LF
                           data

               See below for a detailed description of the data command.

           In both formats <mode> is the type of file entry, specified in
           octal. Git only supports the following modes:

           o   100644 or 644: A normal (not-executable) file. The majority of
               files in most projects use this mode. If in doubt, this is what
               you want.

           o   100755 or 755: A normal, but executable, file.

           o   120000: A symlink, the content of the file will be the link
               target.

           o   160000: A gitlink, SHA-1 of the object refers to a commit in
               another repository. Git links can only be specified by SHA or
               through a commit mark. They are used to implement submodules.

           o   040000: A subdirectory. Subdirectories can only be specified by
               SHA or through a tree mark set with --import-marks.

           In both formats <path> is the complete path of the file to be added
           (if not already existing) or modified (if already existing).

           A <path> string must use UNIX-style directory separators (forward
           slash /), may contain any byte other than LF, and must not start
           with double quote (").

           A path can use C-style string quoting; this is accepted in all
           cases and mandatory if the filename starts with double quote or
           contains LF. In C-style quoting, the complete name should be
           surrounded with double quotes, and any LF, backslash, or double
           quote characters must be escaped by preceding them with a backslash
           (e.g., "path/with\n, \\ and \" in it").

           The value of <path> must be in canonical form. That is it must not:

           o   contain an empty directory component (e.g.  foo//bar is
               invalid),

           o   end with a directory separator (e.g.  foo/ is invalid),

           o   start with a directory separator (e.g.  /foo is invalid),

           o   contain the special component .  or ..  (e.g.  foo/./bar and
               foo/../bar are invalid).

           The root of the tree can be represented by an empty string as
           <path>.

           It is recommended that <path> always be encoded using UTF-8.

       filedelete
           Included in a commit command to remove a file or recursively delete
           an entire directory from the branch. If the file or directory
           removal makes its parent directory empty, the parent directory will
           be automatically removed too. This cascades up the tree until the
           first non-empty directory or the root is reached.

                       'D' SP <path> LF

           here <path> is the complete path of the file or subdirectory to be
           removed from the branch. See filemodify above for a detailed
           description of <path>.

       filecopy
           Recursively copies an existing file or subdirectory to a different
           location within the branch. The existing file or directory must
           exist. If the destination exists it will be completely replaced by
           the content copied from the source.

                       'C' SP <path> SP <path> LF

           here the first <path> is the source location and the second <path>
           is the destination. See filemodify above for a detailed description
           of what <path> may look like. To use a source path that contains SP
           the path must be quoted.

           A filecopy command takes effect immediately. Once the source
           location has been copied to the destination any future commands
           applied to the source location will not impact the destination of
           the copy.

       filerename
           Renames an existing file or subdirectory to a different location
           within the branch. The existing file or directory must exist. If
           the destination exists it will be replaced by the source directory.

                       'R' SP <path> SP <path> LF

           here the first <path> is the source location and the second <path>
           is the destination. See filemodify above for a detailed description
           of what <path> may look like. To use a source path that contains SP
           the path must be quoted.

           A filerename command takes effect immediately. Once the source
           location has been renamed to the destination any future commands
           applied to the source location will create new files there and not
           impact the destination of the rename.

           Note that a filerename is the same as a filecopy followed by a
           filedelete of the source location. There is a slight performance
           advantage to using filerename, but the advantage is so small that
           it is never worth trying to convert a delete/add pair in source
           material into a rename for fast-import. This filerename command is
           provided just to simplify frontends that already have rename
           information and don't want bother with decomposing it into a
           filecopy followed by a filedelete.

       filedeleteall
           Included in a commit command to remove all files (and also all
           directories) from the branch. This command resets the internal
           branch structure to have no files in it, allowing the frontend to
           subsequently add all interesting files from scratch.

                       'deleteall' LF

           This command is extremely useful if the frontend does not know (or
           does not care to know) what files are currently on the branch, and
           therefore cannot generate the proper filedelete commands to update
           the content.

           Issuing a filedeleteall followed by the needed filemodify commands
           to set the correct content will produce the same results as sending
           only the needed filemodify and filedelete commands. The
           filedeleteall approach may however require fast-import to use
           slightly more memory per active branch (less than 1 MiB for even
           most large projects); so frontends that can easily obtain only the
           affected paths for a commit are encouraged to do so.

       notemodify
           Included in a commit <notes_ref> command to add a new note
           annotating a <commit-ish> or change this annotation contents.
           Internally it is similar to filemodify 100644 on <commit-ish> path
           (maybe split into subdirectories). It's not advised to use any
           other commands to write to the <notes_ref> tree except
           filedeleteall to delete all existing notes in this tree. This
           command has two different means of specifying the content of the
           note.

           External data format
               The data content for the note was already supplied by a prior
               blob command. The frontend just needs to connect it to the
               commit that is to be annotated.

                           'N' SP <dataref> SP <commit-ish> LF

               Here <dataref> can be either a mark reference (:<idnum>) set by
               a prior blob command, or a full 40-byte SHA-1 of an existing
               Git blob object.

           Inline data format
               The data content for the note has not been supplied yet. The
               frontend wants to supply it as part of this modify command.

                           'N' SP 'inline' SP <commit-ish> LF
                           data

               See below for a detailed description of the data command.

           In both formats <commit-ish> is any of the commit specification
           expressions also accepted by from (see above).

   mark
       Arranges for fast-import to save a reference to the current object,
       allowing the frontend to recall this object at a future point in time,
       without knowing its SHA-1. Here the current object is the object
       creation command the mark command appears within. This can be commit,
       tag, and blob, but commit is the most common usage.

                   'mark' SP ':' <idnum> LF

       where <idnum> is the number assigned by the frontend to this mark. The
       value of <idnum> is expressed as an ASCII decimal integer. The value 0
       is reserved and cannot be used as a mark. Only values greater than or
       equal to 1 may be used as marks.

       New marks are created automatically. Existing marks can be moved to
       another object simply by reusing the same <idnum> in another mark
       command.

   tag
       Creates an annotated tag referring to a specific commit. To create
       lightweight (non-annotated) tags see the reset command below.

                   'tag' SP <name> LF
                   'from' SP <commit-ish> LF
                   'tagger' (SP <name>)? SP LT <email> GT SP <when> LF
                   data

       where <name> is the name of the tag to create.

       Tag names are automatically prefixed with refs/tags/ when stored in
       Git, so importing the CVS branch symbol RELENG-1_0-FINAL would use just
       RELENG-1_0-FINAL for <name>, and fast-import will write the
       corresponding ref as refs/tags/RELENG-1_0-FINAL.

       The value of <name> must be a valid refname in Git and therefore may
       contain forward slashes. As LF is not valid in a Git refname, no
       quoting or escaping syntax is supported here.

       The from command is the same as in the commit command; see above for
       details.

       The tagger command uses the same format as committer within commit;
       again see above for details.

       The data command following tagger must supply the annotated tag message
       (see below for data command syntax). To import an empty tag message use
       a 0 length data. Tag messages are free-form and are not interpreted by
       Git. Currently they must be encoded in UTF-8, as fast-import does not
       permit other encodings to be specified.

       Signing annotated tags during import from within fast-import is not
       supported. Trying to include your own PGP/GPG signature is not
       recommended, as the frontend does not (easily) have access to the
       complete set of bytes which normally goes into such a signature. If
       signing is required, create lightweight tags from within fast-import
       with reset, then create the annotated versions of those tags offline
       with the standard git tag process.

   reset
       Creates (or recreates) the named branch, optionally starting from a
       specific revision. The reset command allows a frontend to issue a new
       from command for an existing branch, or to create a new branch from an
       existing commit without creating a new commit.

                   'reset' SP <ref> LF
                   ('from' SP <commit-ish> LF)?
                   LF?

       For a detailed description of <ref> and <commit-ish> see above under
       commit and from.

       The LF after the command is optional (it used to be required).

       The reset command can also be used to create lightweight
       (non-annotated) tags. For example:

           reset refs/tags/938
           from :938

       would create the lightweight tag refs/tags/938 referring to whatever
       commit mark :938 references.

   blob
       Requests writing one file revision to the packfile. The revision is not
       connected to any commit; this connection must be formed in a subsequent
       commit command by referencing the blob through an assigned mark.

                   'blob' LF
                   mark?
                   data

       The mark command is optional here as some frontends have chosen to
       generate the Git SHA-1 for the blob on their own, and feed that
       directly to commit. This is typically more work than it's worth
       however, as marks are inexpensive to store and easy to use.

   data
       Supplies raw data (for use as blob/file content, commit messages, or
       annotated tag messages) to fast-import. Data can be supplied using an
       exact byte count or delimited with a terminating line. Real frontends
       intended for production-quality conversions should always use the exact
       byte count format, as it is more robust and performs better. The
       delimited format is intended primarily for testing fast-import.

       Comment lines appearing within the <raw> part of data commands are
       always taken to be part of the body of the data and are therefore never
       ignored by fast-import. This makes it safe to import any file/message
       content whose lines might start with #.

       Exact byte count format
           The frontend must specify the number of bytes of data.

                       'data' SP <count> LF
                       <raw> LF?

           where <count> is the exact number of bytes appearing within <raw>.
           The value of <count> is expressed as an ASCII decimal integer. The
           LF on either side of <raw> is not included in <count> and will not
           be included in the imported data.

           The LF after <raw> is optional (it used to be required) but
           recommended. Always including it makes debugging a fast-import
           stream easier as the next command always starts in column 0 of the
           next line, even if <raw> did not end with an LF.

       Delimited format
           A delimiter string is used to mark the end of the data. fast-import
           will compute the length by searching for the delimiter. This format
           is primarily useful for testing and is not recommended for real
           data.

                       'data' SP '<<' <delim> LF
                       <raw> LF
                       <delim> LF
                       LF?

           where <delim> is the chosen delimiter string. The string <delim>
           must not appear on a line by itself within <raw>, as otherwise
           fast-import will think the data ends earlier than it really does.
           The LF immediately trailing <raw> is part of <raw>. This is one of
           the limitations of the delimited format, it is impossible to supply
           a data chunk which does not have an LF as its last byte.

           The LF after <delim> LF is optional (it used to be required).

   checkpoint
       Forces fast-import to close the current packfile, start a new one, and
       to save out all current branch refs, tags and marks.

                   'checkpoint' LF
                   LF?

       Note that fast-import automatically switches packfiles when the current
       packfile reaches --max-pack-size, or 4 GiB, whichever limit is smaller.
       During an automatic packfile switch fast-import does not update the
       branch refs, tags or marks.

       As a checkpoint can require a significant amount of CPU time and disk
       IO (to compute the overall pack SHA-1 checksum, generate the
       corresponding index file, and update the refs) it can easily take
       several minutes for a single checkpoint command to complete.

       Frontends may choose to issue checkpoints during extremely large and
       long running imports, or when they need to allow another Git process
       access to a branch. However given that a 30 GiB Subversion repository
       can be loaded into Git through fast-import in about 3 hours, explicit
       checkpointing may not be necessary.

       The LF after the command is optional (it used to be required).

   progress
       Causes fast-import to print the entire progress line unmodified to its
       standard output channel (file descriptor 1) when the command is
       processed from the input stream. The command otherwise has no impact on
       the current import, or on any of fast-import's internal state.

                   'progress' SP <any> LF
                   LF?

       The <any> part of the command may contain any sequence of bytes that
       does not contain LF. The LF after the command is optional. Callers may
       wish to process the output through a tool such as sed to remove the
       leading part of the line, for example:

           frontend | git fast-import | sed 's/^progress //'

       Placing a progress command immediately after a checkpoint will inform
       the reader when the checkpoint has been completed and it can safely
       access the refs that fast-import updated.

   get-mark
       Causes fast-import to print the SHA-1 corresponding to a mark to stdout
       or to the file descriptor previously arranged with the --cat-blob-fd
       argument. The command otherwise has no impact on the current import;
       its purpose is to retrieve SHA-1s that later commits might want to
       refer to in their commit messages.

                   'get-mark' SP ':' <idnum> LF

       This command can be used anywhere in the stream that comments are
       accepted. In particular, the get-mark command can be used in the middle
       of a commit but not in the middle of a data command.

       See "Responses To Commands" below for details about how to read this
       output safely.

   cat-blob
       Causes fast-import to print a blob to a file descriptor previously
       arranged with the --cat-blob-fd argument. The command otherwise has no
       impact on the current import; its main purpose is to retrieve blobs
       that may be in fast-import's memory but not accessible from the target
       repository.

                   'cat-blob' SP <dataref> LF

       The <dataref> can be either a mark reference (:<idnum>) set previously
       or a full 40-byte SHA-1 of a Git blob, preexisting or ready to be
       written.

       Output uses the same format as git cat-file --batch:

           <sha1> SP 'blob' SP <size> LF
           <contents> LF

       This command can be used anywhere in the stream that comments are
       accepted. In particular, the cat-blob command can be used in the middle
       of a commit but not in the middle of a data command.

       See "Responses To Commands" below for details about how to read this
       output safely.

   ls
       Prints information about the object at a path to a file descriptor
       previously arranged with the --cat-blob-fd argument. This allows
       printing a blob from the active commit (with cat-blob) or copying a
       blob or tree from a previous commit for use in the current one (with
       filemodify).

       The ls command can be used anywhere in the stream that comments are
       accepted, including the middle of a commit.

       Reading from the active commit
           This form can only be used in the middle of a commit. The path
           names a directory entry within fast-import's active commit. The
           path must be quoted in this case.

                       'ls' SP <path> LF

       Reading from a named tree
           The <dataref> can be a mark reference (:<idnum>) or the full
           40-byte SHA-1 of a Git tag, commit, or tree object, preexisting or
           waiting to be written. The path is relative to the top level of the
           tree named by <dataref>.

                       'ls' SP <dataref> SP <path> LF

       See filemodify above for a detailed description of <path>.

       Output uses the same format as git ls-tree <tree> -- <path>:

           <mode> SP ('blob' | 'tree' | 'commit') SP <dataref> HT <path> LF

       The <dataref> represents the blob, tree, or commit object at <path> and
       can be used in later get-mark, cat-blob, filemodify, or ls commands.

       If there is no file or subtree at that path, git fast-import will
       instead report

           missing SP <path> LF

       See "Responses To Commands" below for details about how to read this
       output safely.

   feature
       Require that fast-import supports the specified feature, or abort if it
       does not.

                   'feature' SP <feature> ('=' <argument>)? LF

       The <feature> part of the command may be any one of the following:

       date-format, export-marks, relative-marks, no-relative-marks, force
           Act as though the corresponding command-line option with a leading
           -- was passed on the command line (see OPTIONS, above).

       import-marks, import-marks-if-exists
           Like --import-marks except in two respects: first, only one
           "feature import-marks" or "feature import-marks-if-exists" command
           is allowed per stream; second, an --import-marks= or
           --import-marks-if-exists command-line option overrides any of these
           "feature" commands in the stream; third, "feature
           import-marks-if-exists" like a corresponding command-line option
           silently skips a nonexistent file.

       get-mark, cat-blob, ls
           Require that the backend support the get-mark, cat-blob, or ls
           command respectively. Versions of fast-import not supporting the
           specified command will exit with a message indicating so. This lets
           the import error out early with a clear message, rather than
           wasting time on the early part of an import before the unsupported
           command is detected.

       notes
           Require that the backend support the notemodify (N) subcommand to
           the commit command. Versions of fast-import not supporting notes
           will exit with a message indicating so.

       done
           Error out if the stream ends without a done command. Without this
           feature, errors causing the frontend to end abruptly at a
           convenient point in the stream can go undetected. This may occur,
           for example, if an import front end dies in mid-operation without
           emitting SIGTERM or SIGKILL at its subordinate git fast-import
           instance.

   option
       Processes the specified option so that git fast-import behaves in a way
       that suits the frontend's needs. Note that options specified by the
       frontend are overridden by any options the user may specify to git
       fast-import itself.

               'option' SP <option> LF

       The <option> part of the command may contain any of the options listed
       in the OPTIONS section that do not change import semantics, without the
       leading -- and is treated in the same way.

       Option commands must be the first commands on the input (not counting
       feature commands), to give an option command after any non-option
       command is an error.

       The following command-line options change import semantics and may
       therefore not be passed as option:

       o   date-format

       o   import-marks

       o   export-marks

       o   cat-blob-fd

       o   force

   done
       If the done feature is not in use, treated as if EOF was read. This can
       be used to tell fast-import to finish early.

       If the --done command-line option or feature done command is in use,
       the done command is mandatory and marks the end of the stream.

RESPONSES TO COMMANDS
       New objects written by fast-import are not available immediately. Most
       fast-import commands have no visible effect until the next checkpoint
       (or completion). The frontend can send commands to fill fast-import's
       input pipe without worrying about how quickly they will take effect,
       which improves performance by simplifying scheduling.

       For some frontends, though, it is useful to be able to read back data
       from the current repository as it is being updated (for example when
       the source material describes objects in terms of patches to be applied
       to previously imported objects). This can be accomplished by connecting
       the frontend and fast-import via bidirectional pipes:

           mkfifo fast-import-output
           frontend <fast-import-output |
           git fast-import >fast-import-output

       A frontend set up this way can use progress, get-mark, ls, and cat-blob
       commands to read information from the import in progress.

       To avoid deadlock, such frontends must completely consume any pending
       output from progress, ls, get-mark, and cat-blob before performing
       writes to fast-import that might block.

CRASH REPORTS
       If fast-import is supplied invalid input it will terminate with a
       non-zero exit status and create a crash report in the top level of the
       Git repository it was importing into. Crash reports contain a snapshot
       of the internal fast-import state as well as the most recent commands
       that lead up to the crash.

       All recent commands (including stream comments, file changes and
       progress commands) are shown in the command history within the crash
       report, but raw file data and commit messages are excluded from the
       crash report. This exclusion saves space within the report file and
       reduces the amount of buffering that fast-import must perform during
       execution.

       After writing a crash report fast-import will close the current
       packfile and export the marks table. This allows the frontend developer
       to inspect the repository state and resume the import from the point
       where it crashed. The modified branches and tags are not updated during
       a crash, as the import did not complete successfully. Branch and tag
       information can be found in the crash report and must be applied
       manually if the update is needed.

       An example crash:

           $ cat >in <<END_OF_INPUT
           # my very first test commit
           commit refs/heads/master
           committer Shawn O. Pearce <spearce> 19283 -0400
           # who is that guy anyway?
           data <<EOF
           this is my commit
           EOF
           M 644 inline .gitignore
           data <<EOF
           .gitignore
           EOF
           M 777 inline bob
           END_OF_INPUT

           $ git fast-import <in
           fatal: Corrupt mode: M 777 inline bob
           fast-import: dumping crash report to .git/fast_import_crash_8434

           $ cat .git/fast_import_crash_8434
           fast-import crash report:
               fast-import process: 8434
               parent process     : 1391
               at Sat Sep 1 00:58:12 2007

           fatal: Corrupt mode: M 777 inline bob

           Most Recent Commands Before Crash
           ---------------------------------
             # my very first test commit
             commit refs/heads/master
             committer Shawn O. Pearce <spearce> 19283 -0400
             # who is that guy anyway?
             data <<EOF
             M 644 inline .gitignore
             data <<EOF
           * M 777 inline bob

           Active Branch LRU
           -----------------
               active_branches = 1 cur, 5 max

           pos  clock name
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            1)      0 refs/heads/master

           Inactive Branches
           -----------------
           refs/heads/master:
             status      : active loaded dirty
             tip commit  : 0000000000000000000000000000000000000000
             old tree    : 0000000000000000000000000000000000000000
             cur tree    : 0000000000000000000000000000000000000000
             commit clock: 0
             last pack   :

           -------------------
           END OF CRASH REPORT

TIPS AND TRICKS
       The following tips and tricks have been collected from various users of
       fast-import, and are offered here as suggestions.

   Use One Mark Per Commit
       When doing a repository conversion, use a unique mark per commit (mark
       :<n>) and supply the --export-marks option on the command line.
       fast-import will dump a file which lists every mark and the Git object
       SHA-1 that corresponds to it. If the frontend can tie the marks back to
       the source repository, it is easy to verify the accuracy and
       completeness of the import by comparing each Git commit to the
       corresponding source revision.

       Coming from a system such as Perforce or Subversion this should be
       quite simple, as the fast-import mark can also be the Perforce
       changeset number or the Subversion revision number.

   Freely Skip Around Branches
       Don't bother trying to optimize the frontend to stick to one branch at
       a time during an import. Although doing so might be slightly faster for
       fast-import, it tends to increase the complexity of the frontend code
       considerably.

       The branch LRU builtin to fast-import tends to behave very well, and
       the cost of activating an inactive branch is so low that bouncing
       around between branches has virtually no impact on import performance.

   Handling Renames
       When importing a renamed file or directory, simply delete the old
       name(s) and modify the new name(s) during the corresponding commit. Git
       performs rename detection after-the-fact, rather than explicitly during
       a commit.

   Use Tag Fixup Branches
       Some other SCM systems let the user create a tag from multiple files
       which are not from the same commit/changeset. Or to create tags which
       are a subset of the files available in the repository.

       Importing these tags as-is in Git is impossible without making at least
       one commit which "fixes up" the files to match the content of the tag.
       Use fast-import's reset command to reset a dummy branch outside of your
       normal branch space to the base commit for the tag, then commit one or
       more file fixup commits, and finally tag the dummy branch.

       For example since all normal branches are stored under refs/heads/ name
       the tag fixup branch TAG_FIXUP. This way it is impossible for the fixup
       branch used by the importer to have namespace conflicts with real
       branches imported from the source (the name TAG_FIXUP is not
       refs/heads/TAG_FIXUP).

       When committing fixups, consider using merge to connect the commit(s)
       which are supplying file revisions to the fixup branch. Doing so will
       allow tools such as git blame to track through the real commit history
       and properly annotate the source files.

       After fast-import terminates the frontend will need to do rm
       .git/TAG_FIXUP to remove the dummy branch.

   Import Now, Repack Later
       As soon as fast-import completes the Git repository is completely valid
       and ready for use. Typically this takes only a very short time, even
       for considerably large projects (100,000+ commits).

       However repacking the repository is necessary to improve data locality
       and access performance. It can also take hours on extremely large
       projects (especially if -f and a large --window parameter is used).
       Since repacking is safe to run alongside readers and writers, run the
       repack in the background and let it finish when it finishes. There is
       no reason to wait to explore your new Git project!

       If you choose to wait for the repack, don't try to run benchmarks or
       performance tests until repacking is completed. fast-import outputs
       suboptimal packfiles that are simply never seen in real use situations.

   Repacking Historical Data
       If you are repacking very old imported data (e.g. older than the last
       year), consider expending some extra CPU time and supplying --window=50
       (or higher) when you run git repack. This will take longer, but will
       also produce a smaller packfile. You only need to expend the effort
       once, and everyone using your project will benefit from the smaller
       repository.

   Include Some Progress Messages
       Every once in a while have your frontend emit a progress message to
       fast-import. The contents of the messages are entirely free-form, so
       one suggestion would be to output the current month and year each time
       the current commit date moves into the next month. Your users will feel
       better knowing how much of the data stream has been processed.

PACKFILE OPTIMIZATION
       When packing a blob fast-import always attempts to deltify against the
       last blob written. Unless specifically arranged for by the frontend,
       this will probably not be a prior version of the same file, so the
       generated delta will not be the smallest possible. The resulting
       packfile will be compressed, but will not be optimal.

       Frontends which have efficient access to all revisions of a single file
       (for example reading an RCS/CVS ,v file) can choose to supply all
       revisions of that file as a sequence of consecutive blob commands. This
       allows fast-import to deltify the different file revisions against each
       other, saving space in the final packfile. Marks can be used to later
       identify individual file revisions during a sequence of commit
       commands.

       The packfile(s) created by fast-import do not encourage good disk
       access patterns. This is caused by fast-import writing the data in the
       order it is received on standard input, while Git typically organizes
       data within packfiles to make the most recent (current tip) data appear
       before historical data. Git also clusters commits together, speeding up
       revision traversal through better cache locality.

       For this reason it is strongly recommended that users repack the
       repository with git repack -a -d after fast-import completes, allowing
       Git to reorganize the packfiles for faster data access. If blob deltas
       are suboptimal (see above) then also adding the -f option to force
       recomputation of all deltas can significantly reduce the final packfile
       size (30-50% smaller can be quite typical).

MEMORY UTILIZATION
       There are a number of factors which affect how much memory fast-import
       requires to perform an import. Like critical sections of core Git,
       fast-import uses its own memory allocators to amortize any overheads
       associated with malloc. In practice fast-import tends to amortize any
       malloc overheads to 0, due to its use of large block allocations.

   per object
       fast-import maintains an in-memory structure for every object written
       in this execution. On a 32 bit system the structure is 32 bytes, on a
       64 bit system the structure is 40 bytes (due to the larger pointer
       sizes). Objects in the table are not deallocated until fast-import
       terminates. Importing 2 million objects on a 32 bit system will require
       approximately 64 MiB of memory.

       The object table is actually a hashtable keyed on the object name (the
       unique SHA-1). This storage configuration allows fast-import to reuse
       an existing or already written object and avoid writing duplicates to
       the output packfile. Duplicate blobs are surprisingly common in an
       import, typically due to branch merges in the source.

   per mark
       Marks are stored in a sparse array, using 1 pointer (4 bytes or 8
       bytes, depending on pointer size) per mark. Although the array is
       sparse, frontends are still strongly encouraged to use marks between 1
       and n, where n is the total number of marks required for this import.

   per branch
       Branches are classified as active and inactive. The memory usage of the
       two classes is significantly different.

       Inactive branches are stored in a structure which uses 96 or 120 bytes
       (32 bit or 64 bit systems, respectively), plus the length of the branch
       name (typically under 200 bytes), per branch. fast-import will easily
       handle as many as 10,000 inactive branches in under 2 MiB of memory.

       Active branches have the same overhead as inactive branches, but also
       contain copies of every tree that has been recently modified on that
       branch. If subtree include has not been modified since the branch
       became active, its contents will not be loaded into memory, but if
       subtree src has been modified by a commit since the branch became
       active, then its contents will be loaded in memory.

       As active branches store metadata about the files contained on that
       branch, their in-memory storage size can grow to a considerable size
       (see below).

       fast-import automatically moves active branches to inactive status
       based on a simple least-recently-used algorithm. The LRU chain is
       updated on each commit command. The maximum number of active branches
       can be increased or decreased on the command line with
       --active-branches=.

   per active tree
       Trees (aka directories) use just 12 bytes of memory on top of the
       memory required for their entries (see "per active file" below). The
       cost of a tree is virtually 0, as its overhead amortizes out over the
       individual file entries.

   per active file entry
       Files (and pointers to subtrees) within active trees require 52 or 64
       bytes (32/64 bit platforms) per entry. To conserve space, file and tree
       names are pooled in a common string table, allowing the filename
       "Makefile" to use just 16 bytes (after including the string header
       overhead) no matter how many times it occurs within the project.

       The active branch LRU, when coupled with the filename string pool and
       lazy loading of subtrees, allows fast-import to efficiently import
       projects with 2,000+ branches and 45,114+ files in a very limited
       memory footprint (less than 2.7 MiB per active branch).

SIGNALS
       Sending SIGUSR1 to the git fast-import process ends the current
       packfile early, simulating a checkpoint command. The impatient operator
       can use this facility to peek at the objects and refs from an import in
       progress, at the cost of some added running time and worse compression.

SEE ALSO
       git-fast-export(1)

GIT
       Part of the git(1) suite

Git 2.14.2                        09/26/2017                GIT-FAST-IMPORT(1)

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