git-pack-objects(1) Git Manual git-pack-objects(1)
NAME
git-pack-objects - Create a packed archive of objects
SYNOPSIS
git pack-objects [-q | --progress | --all-progress] [--all-progress-implied]
[--no-reuse-delta] [--delta-base-offset] [--non-empty]
[--local] [--incremental] [--window=<n>] [--depth=<n>]
[--revs [--unpacked | --all]] [--keep-pack=<pack-name>]
[--cruft] [--cruft-expiration=<time>]
[--stdout [--filter=<filter-spec>] | <base-name>]
[--shallow] [--keep-true-parents] [--[no-]sparse]
[--name-hash-version=<n>] [--path-walk] <
DESCRIPTION
Reads list of objects from the standard input, and writes either one or
more packed archives with the specified base-name to disk, or a packed
archive to the standard output.
A packed archive is an efficient way to transfer a set of objects between
two repositories as well as an access efficient archival format. In a
packed archive, an object is either stored as a compressed whole or as a
difference from some other object. The latter is often called a delta.
The packed archive format (.pack) is designed to be self-contained so
that it can be unpacked without any further information. Therefore, each
object that a delta depends upon must be present within the pack.
A pack index file (.idx) is generated for fast, random access to the
objects in the pack. Placing both the index file (.idx) and the packed
archive (.pack) in the pack/ subdirectory of $GIT_OBJECT_DIRECTORY (or
any of the directories on $GIT_ALTERNATE_OBJECT_DIRECTORIES) enables Git
to read from the pack archive.
The git unpack-objects command can read the packed archive and expand the
objects contained in the pack into "one-file one-object" format; this is
typically done by the smart-pull commands when a pack is created
on-the-fly for efficient network transport by their peers.
OPTIONS
base-name
Write into pairs of files (.pack and .idx), using <base-name> to
determine the name of the created file. When this option is used, the
two files in a pair are written in <base-name>-<SHA-1>.{pack,idx}
files. <SHA-1> is a hash based on the pack content and is written to
the standard output of the command.
--stdout
Write the pack contents (what would have been written to .pack file)
out to the standard output.
--revs
Read the revision arguments from the standard input, instead of
individual object names. The revision arguments are processed the
same way as git rev-list with the --objects flag uses its commit
arguments to build the list of objects it outputs. The objects on the
resulting list are packed. Besides revisions, --not or --shallow
<SHA-1> lines are also accepted.
--unpacked
This implies --revs. When processing the list of revision arguments
read from the standard input, limit the objects packed to those that
are not already packed.
--all
This implies --revs. In addition to the list of revision arguments
read from the standard input, pretend as if all refs under refs/ are
specified to be included.
--include-tag
Include unasked-for annotated tags if the object they reference was
included in the resulting packfile. This can be useful to send new
tags to native Git clients.
--stdin-packs[=<mode>]
Read the basenames of packfiles (e.g., pack-1234abcd.pack) from the
standard input, instead of object names or revision arguments. The
resulting pack contains all objects listed in the included packs
(those not beginning with ^), excluding any objects listed in the
excluded packs (beginning with ^).
When mode is "follow" packs may additionally be prefixed with !,
indicating that they are excluded but not necessarily closed under
reachability. In addition to objects in included packs, the resulting
pack may include additional objects based on the following:
o If any packs are marked with !, then objects reachable from such
packs or included ones via objects outside of excluded-closed
packs will be included. In this case, all ^ packs are treated as
closed under reachability.
o Otherwise (if there are no ! packs), objects within unlisted
packs will be included if those objects are (1) reachable from
the included packs, and (2) not found in any excluded packs.
This mode is useful, for example, to resurrect once-unreachable
objects found in cruft packs to generate packs which are closed under
reachability up to the boundary set by the excluded packs.
Incompatible with --revs, or options that imply --revs (such as
--all), with the exception of --unpacked, which is compatible.
--cruft
Packs unreachable objects into a separate "cruft" pack, denoted by
the existence of a .mtimes file. Typically used by git repack
--cruft. Callers provide a list of pack names and indicate which
packs will remain in the repository, along with which packs will be
deleted (indicated by the - prefix). The contents of the cruft pack
are all objects not contained in the surviving packs which have not
exceeded the grace period (see --cruft-expiration below), or which
have exceeded the grace period, but are reachable from an other
object which hasn't.
When the input lists a pack containing all reachable objects (and
lists all other packs as pending deletion), the corresponding cruft
pack will contain all unreachable objects (with mtime newer than the
--cruft-expiration) along with any unreachable objects whose mtime is
older than the --cruft-expiration, but are reachable from an
unreachable object whose mtime is newer than the --cruft-expiration).
Incompatible with --unpack-unreachable, --keep-unreachable,
--pack-loose-unreachable, --stdin-packs, as well as any other options
which imply --revs.
--cruft-expiration=<approxidate>
If specified, objects are eliminated from the cruft pack if they have
an mtime older than <approxidate>. If unspecified (and given
--cruft), then no objects are eliminated.
--window=<n>, --depth=<n>
These two options affect how the objects contained in the pack are
stored using delta compression. The objects are first internally
sorted by type, size and optionally names and compared against the
other objects within --window to see if using delta compression saves
space. --depth limits the maximum delta depth; making it too deep
affects the performance on the unpacker side, because delta data
needs to be applied that many times to get to the necessary object.
The default value for --window is 10 and --depth is 50. The maximum
depth is 4095.
--window-memory=<n>
This option provides an additional limit on top of --window; the
window size will dynamically scale down so as to not take up more
than <n> bytes in memory. This is useful in repositories with a mix
of large and small objects to not run out of memory with a large
window, but still be able to take advantage of the large window for
the smaller objects. The size can be suffixed with "k", "m", or "g".
--window-memory=0 makes memory usage unlimited. The default is taken
from the pack.windowMemory configuration variable.
--max-pack-size=<n>
In unusual scenarios, you may not be able to create files larger than
a certain size on your filesystem, and this option can be used to
tell the command to split the output packfile into multiple
independent packfiles, each not larger than the given size. The size
can be suffixed with "k", "m", or "g". The minimum size allowed is
limited to 1 MiB. The default is unlimited, unless the config
variable pack.packSizeLimit is set. Note that this option may result
in a larger and slower repository; see the discussion in
pack.packSizeLimit.
--honor-pack-keep
This flag causes an object already in a local pack that has a .keep
file to be ignored, even if it would have otherwise been packed.
--keep-pack=<pack-name>
This flag causes an object already in the given pack to be ignored,
even if it would have otherwise been packed. <pack-name> is the pack
file name without leading directory (e.g. pack-123.pack). The option
could be specified multiple times to keep multiple packs.
--incremental
This flag causes an object already in a pack to be ignored even if it
would have otherwise been packed.
--local
This flag causes an object that is borrowed from an alternate object
store to be ignored even if it would have otherwise been packed.
--non-empty
Only create a packed archive if it would contain at least one object.
--progress
Progress status is reported on the standard error stream by default
when it is attached to a terminal, unless -q is specified. This flag
forces progress status even if the standard error stream is not
directed to a terminal.
--all-progress
When --stdout is specified then progress report is displayed during
the object count and compression phases but inhibited during the
write-out phase. The reason is that in some cases the output stream
is directly linked to another command which may wish to display
progress status of its own as it processes incoming pack data. This
flag is like --progress except that it forces progress report for the
write-out phase as well even if --stdout is used.
--all-progress-implied
This is used to imply --all-progress whenever progress display is
activated. Unlike --all-progress this flag doesn't actually force any
progress display by itself.
-q
This flag makes the command not to report its progress on the
standard error stream.
--no-reuse-delta
When creating a packed archive in a repository that has existing
packs, the command reuses existing deltas. This sometimes results in
a slightly suboptimal pack. This flag tells the command not to reuse
existing deltas but compute them from scratch.
--no-reuse-object
This flag tells the command not to reuse existing object data at all,
including non deltified object, forcing recompression of everything.
This implies --no-reuse-delta. Useful only in the obscure case where
wholesale enforcement of a different compression level on the packed
data is desired.
--compression=<n>
Specifies compression level for newly-compressed data in the
generated pack. If not specified, pack compression level is
determined first by pack.compression, then by core.compression, and
defaults to -1, the zlib default, if neither is set. Add
--no-reuse-object if you want to force a uniform compression level on
all data no matter the source.
--sparse, --no-sparse
Toggle the "sparse" algorithm to determine which objects to include
in the pack, when combined with the "--revs" option. This algorithm
only walks trees that appear in paths that introduce new objects.
This can have significant performance benefits when computing a pack
to send a small change. However, it is possible that extra objects
are added to the pack-file if the included commits contain certain
types of direct renames. If this option is not included, it defaults
to the value of pack.useSparse, which is true unless otherwise
specified.
--thin
Create a "thin" pack by omitting the common objects between a sender
and a receiver in order to reduce network transfer. This option only
makes sense in conjunction with --stdout.
Note: A thin pack violates the packed archive format by omitting
required objects and is thus unusable by Git without making it
self-contained. Use git index-pack --fix-thin (see git-index-pack(1))
to restore the self-contained property.
--shallow
Optimize a pack that will be provided to a client with a shallow
repository. This option, combined with --thin, can result in a
smaller pack at the cost of speed.
--delta-base-offset
A packed archive can express the base object of a delta as either a
20-byte object name or as an offset in the stream, but ancient
versions of Git don't understand the latter. By default, git
pack-objects only uses the former format for better compatibility.
This option allows the command to use the latter format for
compactness. Depending on the average delta chain length, this option
typically shrinks the resulting packfile by 3-5 per-cent.
Note: Porcelain commands such as git gc (see git-gc(1)), git repack
(see git-repack(1)) pass this option by default in modern Git when
they put objects in your repository into pack files. So does git
bundle (see git-bundle(1)) when it creates a bundle.
--threads=<n>
Specifies the number of threads to spawn when searching for best
delta matches. This requires that pack-objects be compiled with
pthreads otherwise this option is ignored with a warning. This is
meant to reduce packing time on multiprocessor machines. The required
amount of memory for the delta search window is however multiplied by
the number of threads. Specifying 0 will cause Git to auto-detect the
number of CPU's and set the number of threads accordingly.
--index-version=<version>[,<offset>]
This is intended to be used by the test suite only. It allows to
force the version for the generated pack index, and to force 64-bit
index entries on objects located above the given offset.
--keep-true-parents
With this option, parents that are hidden by grafts are packed
nevertheless.
--filter=<filter-spec>
Omits certain objects (usually blobs) from the resulting packfile.
See git-rev-list(1) for valid <filter-spec> forms.
--no-filter
Turns off any previous --filter= argument.
--missing=<missing-action>
A debug option to help with future "partial clone" development. This
option specifies how missing objects are handled.
The form --missing=error requests that pack-objects stop with an
error if a missing object is encountered. If the repository is a
partial clone, an attempt to fetch missing objects will be made
before declaring them missing. This is the default action.
The form --missing=allow-any will allow object traversal to continue
if a missing object is encountered. No fetch of a missing object will
occur. Missing objects will silently be omitted from the results.
The form --missing=allow-promisor is like allow-any, but will only
allow object traversal to continue for EXPECTED promisor missing
objects. No fetch of a missing object will occur. An unexpected
missing object will raise an error.
--exclude-promisor-objects
Omit objects that are known to be in the promisor remote. (This
option has the purpose of operating only on locally created objects,
so that when we repack, we still maintain a distinction between
locally created objects [without .promisor] and objects from the
promisor remote [with .promisor].) This is used with partial clone.
--keep-unreachable
Objects unreachable from the refs in packs named with --unpacked=
option are added to the resulting pack, in addition to the reachable
objects that are not in packs marked with *.keep files. This implies
--revs.
--pack-loose-unreachable
Pack unreachable loose objects (and their loose counterparts
removed). This implies --revs.
--unpack-unreachable
Keep unreachable objects in loose form. This implies --revs.
--delta-islands
Restrict delta matches based on "islands". See DELTA ISLANDS below.
--name-hash-version=<n>
While performing delta compression, Git groups objects that may be
similar based on heuristics using the path to that object. While
grouping objects by an exact path match is good for paths with many
versions, there are benefits for finding delta pairs across different
full paths. Git collects objects by type and then by a "name hash" of
the path and then by size, hoping to group objects that will compress
well together.
The default name hash version is 1, which prioritizes hash locality
by considering the final bytes of the path as providing the maximum
magnitude to the hash function. This version excels at distinguishing
short paths and finding renames across directories. However, the hash
function depends primarily on the final 16 bytes of the path. If
there are many paths in the repo that have the same final 16 bytes
and differ only by parent directory, then this name-hash may lead to
too many collisions and cause poor results. At the moment, this
version is required when writing reachability bitmap files with
--write-bitmap-index.
The name hash version 2 has similar locality features as version 1,
except it considers each path component separately and overlays the
hashes with a shift. This still prioritizes the final bytes of the
path, but also "salts" the lower bits of the hash using the parent
directory names. This method allows for some of the locality benefits
of version 1 while breaking most of the collisions from a
similarly-named file appearing in many different directories. At the
moment, this version is not allowed when writing reachability bitmap
files with --write-bitmap-index and it will be automatically changed
to version 1.
--path-walk
Perform compression by first organizing objects by path, then a
second pass that compresses across paths as normal. This has the
potential to improve delta compression especially in the presence of
filenames that cause collisions in Git's default name-hash algorithm.
When --use-bitmap-index is specified with --path-walk, a successful
bitmap traversal is used for object enumeration, with path-walk
remaining as the fallback traversal when the bitmap cannot satisfy
the request. The --path-walk option supports the --filter=<spec>
forms blob:none, blob:limit=<n>, tree:0, object:type=<type>, and
sparse:<oid>. These supported filter types can be combined with the
combine:<spec>+<spec> form.
DELTA ISLANDS
When possible, pack-objects tries to reuse existing on-disk deltas to
avoid having to search for new ones on the fly. This is an important
optimization for serving fetches, because it means the server can avoid
inflating most objects at all and just send the bytes directly from disk.
This optimization can't work when an object is stored as a delta against
a base which the receiver does not have (and which we are not already
sending). In that case the server "breaks" the delta and has to find a
new one, which has a high CPU cost. Therefore it's important for
performance that the set of objects in on-disk delta relationships match
what a client would fetch.
In a normal repository, this tends to work automatically. The objects are
mostly reachable from the branches and tags, and that's what clients
fetch. Any deltas we find on the server are likely to be between objects
the client has or will have.
But in some repository setups, you may have several related but separate
groups of ref tips, with clients tending to fetch those groups
independently. For example, imagine that you are hosting several "forks"
of a repository in a single shared object store, and letting clients view
them as separate repositories through GIT_NAMESPACE or separate repos
using the alternates mechanism. A naive repack may find that the optimal
delta for an object is against a base that is only found in another fork.
But when a client fetches, they will not have the base object, and we'll
have to find a new delta on the fly.
A similar situation may exist if you have many refs outside of
refs/heads/ and refs/tags/ that point to related objects (e.g., refs/pull
or refs/changes used by some hosting providers). By default, clients
fetch only heads and tags, and deltas against objects found only in those
other groups cannot be sent as-is.
Delta islands solve this problem by allowing you to group your refs into
distinct "islands". Pack-objects computes which objects are reachable
from which islands, and refuses to make a delta from an object A against
a base which is not present in all of A's islands. This results in
slightly larger packs (because we miss some delta opportunities), but
guarantees that a fetch of one island will not have to recompute deltas
on the fly due to crossing island boundaries.
When repacking with delta islands the delta window tends to get clogged
with candidates that are forbidden by the config. Repacking with a big
--window helps (and doesn't take as long as it otherwise might because we
can reject some object pairs based on islands before doing any
computation on the content).
Islands are configured via the pack.island option, which can be specified
multiple times. Each value is a left-anchored regular expressions
matching refnames. For example:
[pack]
island = refs/heads/
island = refs/tags/
puts heads and tags into an island (whose name is the empty string; see
below for more on naming). Any refs which do not match those regular
expressions (e.g., refs/pull/123) is not in any island. Any object which
is reachable only from refs/pull/ (but not heads or tags) is therefore
not a candidate to be used as a base for refs/heads/.
Refs are grouped into islands based on their "names", and two regexes
that produce the same name are considered to be in the same island. The
names are computed from the regexes by concatenating any capture groups
from the regex, with a - dash in between. (And if there are no capture
groups, then the name is the empty string, as in the above example.) This
allows you to create arbitrary numbers of islands. Only up to 14 such
capture groups are supported though.
For example, imagine you store the refs for each fork in refs/virtual/ID,
where ID is a numeric identifier. You might then configure:
[pack]
island = refs/virtual/([0-9]+)/heads/
island = refs/virtual/([0-9]+)/tags/
island = refs/virtual/([0-9]+)/(pull)/
That puts the heads and tags for each fork in their own island (named
"1234" or similar), and the pull refs for each go into their own
"1234-pull".
Note that we pick a single island for each regex to go into, using "last
one wins" ordering (which allows repo-specific config to take precedence
over user-wide config, and so forth).
CONFIGURATION
Various configuration variables affect packing, see git-config(1) (search
for "pack" and "delta").
Notably, delta compression is not used on objects larger than the
core.bigFileThreshold configuration variable and on files with the
attribute delta set to false.
SEE ALSO
git-rev-list(1) git-repack(1) git-prune-packed(1)
GIT
Part of the git(1) suite
Git 2.56.0 2026-09-27 git-pack-objects(1)
git 2.56.0 - Generated Thu Oct 1 16:27:11 CDT 2026
