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Linux 2.6 - man page for git-fast-import (linux section 1)

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

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

       frontend | git fast-import [options]

       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.

	   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).

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

	   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.

	   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
	   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.

	   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.

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

	   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
	   Maximum number of branches to maintain active at once. See "Memory Utilization" below
	   for details. Default is 5.

	   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.

	   Maximum delta depth, for blob and tree deltification. Default is 10.

	   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

	   Maximum size of each output packfile. The default is unlimited.

       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).

       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).

       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.

       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.

       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.

	   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.

	   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.

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

	   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

       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

	   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.

	   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 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.

	   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.

	   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.

	   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.

	   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.

	   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.

	   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.

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

	   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

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

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

       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

       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).

	   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.

	   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

	   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.

	   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.

	   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.

	   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. However Git's other tools never create commits with more than 15 additional
	   ancestors (forming a 16-way merge). For this reason it is suggested that frontends do
	   not use more than 15 merge commands per commit; 16, if starting a new, empty branch.

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

	   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

	       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

	   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.

	   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>.

	   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.

	   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.

	   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.

	   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

	       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).

       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.

       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

       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

       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

       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.

       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)?

       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

	   reset refs/tags/938
	   from :938

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

       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

       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.

       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

	   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).

       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

       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).

       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

		   'progress' SP <any> 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.

       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

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

       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 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.

       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.

       cat-blob, ls
	   Require that the backend support the cat-blob or ls command. 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.

	   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.

	   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.

       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 commandline 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

       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.

       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, 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, and cat-blob before performing writes to fast-import that might block.

       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
	   M 644 inline .gitignore
	   data <<EOF
	   M 777 inline bob

	   $ 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
	     status	 : active loaded dirty
	     tip commit  : 0000000000000000000000000000000000000000
	     old tree	 : 0000000000000000000000000000000000000000
	     cur tree	 : 0000000000000000000000000000000000000000
	     commit clock: 0
	     last pack	 :


       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

   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

   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.

       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).

       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

   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).

       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

       Part of the git(1) suite

Git				    01/14/2014			       GIT-FAST-IMPORT(1)

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