gitformat-index(5) — Linux manual page


GITFORMAT-INDEX(5)             Git Manual             GITFORMAT-INDEX(5)

NAME         top

       gitformat-index - Git index format

SYNOPSIS         top


DESCRIPTION         top

       Git index format


           All binary numbers are in network byte order.
           In a repository using the traditional SHA-1, checksums and object IDs
           (object names) mentioned below are all computed using SHA-1.  Similarly,
           in SHA-256 repositories, these values are computed using SHA-256.
           Version 2 is described here unless stated otherwise.

       •   A 12-byte header consisting of

               4-byte signature:
                 The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache")

               4-byte version number:
                 The current supported versions are 2, 3 and 4.

               32-bit number of index entries.

       •   A number of sorted index entries (see below).

       •   Extensions

               Extensions are identified by signature. Optional extensions can
               be ignored if Git does not understand them.

               4-byte extension signature. If the first byte is 'A'..'Z' the
               extension is optional and can be ignored.

               32-bit size of the extension

               Extension data

       •   Hash checksum over the content of the index file before this

INDEX ENTRY         top

           Index entries are sorted in ascending order on the name field,
           interpreted as a string of unsigned bytes (i.e. memcmp() order, no
           localization, no special casing of directory separator '/'). Entries
           with the same name are sorted by their stage field.

           An index entry typically represents a file. However, if sparse-checkout
           is enabled in cone mode (`core.sparseCheckoutCone` is enabled) and the
           `extensions.sparseIndex` extension is enabled, then the index may
           contain entries for directories outside of the sparse-checkout definition.
           These entries have mode `040000`, include the `SKIP_WORKTREE` bit, and
           the path ends in a directory separator.

           32-bit ctime seconds, the last time a file's metadata changed
             this is stat(2) data

           32-bit ctime nanosecond fractions
             this is stat(2) data

           32-bit mtime seconds, the last time a file's data changed
             this is stat(2) data

           32-bit mtime nanosecond fractions
             this is stat(2) data

           32-bit dev
             this is stat(2) data

           32-bit ino
             this is stat(2) data

           32-bit mode, split into (high to low bits)

           16-bit unused, must be zero

           4-bit object type
             valid values in binary are 1000 (regular file), 1010 (symbolic link)
             and 1110 (gitlink)

           3-bit unused, must be zero

           9-bit unix permission. Only 0755 and 0644 are valid for regular files.
           Symbolic links and gitlinks have value 0 in this field.

           32-bit uid
             this is stat(2) data

           32-bit gid
             this is stat(2) data

           32-bit file size
             This is the on-disk size from stat(2), truncated to 32-bit.

           Object name for the represented object

           A 16-bit 'flags' field split into (high to low bits)

           1-bit assume-valid flag

           1-bit extended flag (must be zero in version 2)

           2-bit stage (during merge)

           12-bit name length if the length is less than 0xFFF; otherwise 0xFFF
           is stored in this field.

           (Version 3 or later) A 16-bit field, only applicable if the
           "extended flag" above is 1, split into (high to low bits).

           1-bit reserved for future

           1-bit skip-worktree flag (used by sparse checkout)

           1-bit intent-to-add flag (used by "git add -N")

           13-bit unused, must be zero

           Entry path name (variable length) relative to top level directory
             (without leading slash). '/' is used as path separator. The special
             path components ".", ".." and ".git" (without quotes) are disallowed.
             Trailing slash is also disallowed.

           The exact encoding is undefined, but the '.' and '/' characters
           are encoded in 7-bit ASCII and the encoding cannot contain a NUL
           byte (iow, this is a UNIX pathname).

           (Version 4) In version 4, the entry path name is prefix-compressed
             relative to the path name for the previous entry (the very first
             entry is encoded as if the path name for the previous entry is an
             empty string).  At the beginning of an entry, an integer N in the
             variable width encoding (the same encoding as the offset is encoded
             for OFS_DELTA pack entries; see linkgit:gitformat-pack[5]) is stored, followed
             by a NUL-terminated string S.  Removing N bytes from the end of the
             path name for the previous entry, and replacing it with the string S
             yields the path name for this entry.

           1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes
           while keeping the name NUL-terminated.

           (Version 4) In version 4, the padding after the pathname does not

           Interpretation of index entries in split index mode is completely
           different. See below for details.

EXTENSIONS         top

   Cache tree
           Since the index does not record entries for directories, the cache
           entries cannot describe tree objects that already exist in the object
           database for regions of the index that are unchanged from an existing
           commit. The cache tree extension stores a recursive tree structure that
           describes the trees that already exist and completely match sections of
           the cache entries. This speeds up tree object generation from the index
           for a new commit by only computing the trees that are "new" to that
           commit. It also assists when comparing the index to another tree, such
           as `HEAD^{tree}`, since sections of the index can be skipped when a tree
           comparison demonstrates equality.

           The recursive tree structure uses nodes that store a number of cache
           entries, a list of subnodes, and an object ID (OID). The OID references
           the existing tree for that node, if it is known to exist. The subnodes
           correspond to subdirectories that themselves have cache tree nodes. The
           number of cache entries corresponds to the number of cache entries in
           the index that describe paths within that tree's directory.

           The extension tracks the full directory structure in the cache tree
           extension, but this is generally smaller than the full cache entry list.

           When a path is updated in index, Git invalidates all nodes of the
           recursive cache tree corresponding to the parent directories of that
           path. We store these tree nodes as being "invalid" by using "-1" as the
           number of cache entries. Invalid nodes still store a span of index
           entries, allowing Git to focus its efforts when reconstructing a full
           cache tree.

           The signature for this extension is { 'T', 'R', 'E', 'E' }.

           A series of entries fill the entire extension; each of which
           consists of:

       •   NUL-terminated path component (relative to its parent

       •   ASCII decimal number of entries in the index that is covered
           by the tree this entry represents (entry_count);

       •   A space (ASCII 32);

       •   ASCII decimal number that represents the number of subtrees
           this tree has;

       •   A newline (ASCII 10); and

       •   Object name for the object that would result from writing
           this span of index as a tree.

               An entry can be in an invalidated state and is represented by having
               a negative number in the entry_count field. In this case, there is no
               object name and the next entry starts immediately after the newline.
               When writing an invalid entry, -1 should always be used as entry_count.

               The entries are written out in the top-down, depth-first order.  The
               first entry represents the root level of the repository, followed by the
               first subtree--let's call this A--of the root level (with its name
               relative to the root level), followed by the first subtree of A (with
               its name relative to A), and so on. The specified number of subtrees
               indicates when the current level of the recursive stack is complete.

   Resolve undo
           A conflict is represented in the index as a set of higher stage entries.
           When a conflict is resolved (e.g. with "git add path"), these higher
           stage entries will be removed and a stage-0 entry with proper resolution
           is added.

           When these higher stage entries are removed, they are saved in the
           resolve undo extension, so that conflicts can be recreated (e.g. with
           "git checkout -m"), in case users want to redo a conflict resolution
           from scratch.

           The signature for this extension is { 'R', 'E', 'U', 'C' }.

           A series of entries fill the entire extension; each of which
           consists of:

       •   NUL-terminated pathname the entry describes (relative to the
           root of the repository, i.e. full pathname);

       •   Three NUL-terminated ASCII octal numbers, entry mode of
           entries in stage 1 to 3 (a missing stage is represented by
           "0" in this field); and

       •   At most three object names of the entry in stages from 1 to 3
           (nothing is written for a missing stage).

   Split index
           In split index mode, the majority of index entries could be stored
           in a separate file. This extension records the changes to be made on
           top of that to produce the final index.

           The signature for this extension is { 'l', 'i', 'n', 'k' }.

           The extension consists of:

       •   Hash of the shared index file. The shared index file path is
           $GIT_DIR/sharedindex.<hash>. If all bits are zero, the index
           does not require a shared index file.

       •   An ewah-encoded delete bitmap, each bit represents an entry
           in the shared index. If a bit is set, its corresponding entry
           in the shared index will be removed from the final index.
           Note, because a delete operation changes index entry
           positions, but we do need original positions in replace
           phase, it’s best to just mark entries for removal, then do a
           mass deletion after replacement.

       •   An ewah-encoded replace bitmap, each bit represents an entry
           in the shared index. If a bit is set, its corresponding entry
           in the shared index will be replaced with an entry in this
           index file. All replaced entries are stored in sorted order
           in this index. The first "1" bit in the replace bitmap
           corresponds to the first index entry, the second "1" bit to
           the second entry and so on. Replaced entries may have empty
           path names to save space.

               The remaining index entries after replaced ones will be added to the
               final index. These added entries are also sorted by entry name then


           Untracked cache saves the untracked file list and necessary data to
           verify the cache. The signature for this extension is { 'U', 'N',
           'T', 'R' }.

           The extension starts with

       •   A sequence of NUL-terminated strings, preceded by the size of
           the sequence in variable width encoding. Each string
           describes the environment where the cache can be used.

       •   Stat data of $GIT_DIR/info/exclude. See "Index entry" section
           from ctime field until "file size".

       •   Stat data of core.excludesFile

       •   32-bit dir_flags (see struct dir_struct)

       •   Hash of $GIT_DIR/info/exclude. A null hash means the file
           does not exist.

       •   Hash of core.excludesFile. A null hash means the file does
           not exist.

       •   NUL-terminated string of per-dir exclude file name. This
           usually is ".gitignore".

       •   The number of following directory blocks, variable width
           encoding. If this number is zero, the extension ends here
           with a following NUL.

       •   A number of directory blocks in depth-first-search order,
           each consists of

       •   The number of untracked entries, variable width encoding.

       •   The number of sub-directory blocks, variable width encoding.

       •   The directory name terminated by NUL.

       •   A number of untracked file/dir names terminated by NUL.

       The remaining data of each directory block is grouped by type:

       •   An ewah bitmap, the n-th bit marks whether the n-th directory
           has valid untracked cache entries.

       •   An ewah bitmap, the n-th bit records "check-only" bit of
           read_directory_recursive() for the n-th directory.

       •   An ewah bitmap, the n-th bit indicates whether hash and stat
           data is valid for the n-th directory and exists in the next

       •   An array of stat data. The n-th data corresponds with the
           n-th "one" bit in the previous ewah bitmap.

       •   An array of hashes. The n-th hash corresponds with the n-th
           "one" bit in the previous ewah bitmap.

       •   One NUL.


           The file system monitor cache tracks files for which the core.fsmonitor
           hook has told us about changes.  The signature for this extension is
           { 'F', 'S', 'M', 'N' }.

           The extension starts with

       •   32-bit version number: the current supported versions are 1
           and 2.

       •   (Version 1) 64-bit time: the extension data reflects all
           changes through the given time which is stored as the
           nanoseconds elapsed since midnight, January 1, 1970.

       •   (Version 2) A null terminated string: an opaque token defined
           by the file system monitor application. The extension data
           reflects all changes relative to that token.

       •   32-bit bitmap size: the size of the CE_FSMONITOR_VALID

       •   An ewah bitmap, the n-th bit indicates whether the n-th index
           entry is not CE_FSMONITOR_VALID.

END OF INDEX ENTRY         top

           The End of Index Entry (EOIE) is used to locate the end of the variable
           length index entries and the beginning of the extensions. Code can take
           advantage of this to quickly locate the index extensions without having
           to parse through all of the index entries.

           Because it must be able to be loaded before the variable length cache
           entries and other index extensions, this extension must be written last.
           The signature for this extension is { 'E', 'O', 'I', 'E' }.

           The extension consists of:

       •   32-bit offset to the end of the index entries

       •   Hash over the extension types and their sizes (but not their
           contents). E.g. if we have "TREE" extension that is N-bytes
           long, "REUC" extension that is M-bytes long, followed by
           "EOIE", then the hash would be:

               Hash("TREE" + <binary representation of N> +
                       "REUC" + <binary representation of M>)


           The Index Entry Offset Table (IEOT) is used to help address the CPU
           cost of loading the index by enabling multi-threading the process of
           converting cache entries from the on-disk format to the in-memory format.
           The signature for this extension is { 'I', 'E', 'O', 'T' }.

           The extension consists of:

       •   32-bit version (currently 1)

       •   A number of index offset entries each consisting of:

       •   32-bit offset from the beginning of the file to the first
           cache entry in this block of entries.

       •   32-bit count of cache entries in this block


           When using sparse-checkout in cone mode, some entire directories within
           the index can be summarized by pointing to a tree object instead of the
           entire expanded list of paths within that tree. An index containing such
           entries is a "sparse index". Index format versions 4 and less were not
           implemented with such entries in mind. Thus, for these versions, an
           index containing sparse directory entries will include this extension
           with signature { 's', 'd', 'i', 'r' }. Like the split-index extension,
           tools should avoid interacting with a sparse index unless they understand
           this extension.

GIT         top

       Part of the git(1) suite

COLOPHON         top

       This page is part of the git (Git distributed version control
       system) project.  Information about the project can be found at
       ⟨⟩.  If you have a bug report for this manual
       page, see ⟨⟩.  This page was obtained
       from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that time,
       the date of the most recent commit that was found in the
       repository was 2023-12-20.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

Git         2023-12-20             GITFORMAT-INDEX(5)

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