From Linux Man Pages
git-fsck-objects - Verifies the connectivity and validity of the objects in the database
SYNOPSIS
git-fsck-objects [--tags] [--root] [--unreachable] [--cache]
[--full] [--strict] [<object>*]
DESCRIPTION
Verifies the connectivity and validity of the objects in the database.
OPTIONS
<object>
An object to treat as the head of an unreachability trace.
If no objects are given, git-fsck-objects defaults to using the index file and all SHA1 references in
.git/refs/* as heads.
--unreachable
Print out objects that exist but that aren't readable from any of the reference nodes.
--root
Report root nodes.
--tags
Report tags.
--cache
Consider any object recorded in the index also as a head node for an unreachability trace.
--full
Check not just objects in GIT_OBJECT_DIRECTORY ($GIT_DIR/objects), but also the ones found in alternate
object pools listed in GIT_ALTERNATE_OBJECT_DIRECTORIES or $GIT_DIR/objects/info/alternates, and in packed
git archives found in $GIT_DIR/objects/pack and corresponding pack subdirectories in alternate object pools.
--strict
Enable more strict checking, namely to catch a file mode recorded with g+w bit set, which was created by
older versions of git. Existing repositories, including the Linux kernel, git itself, and sparse repository
have old objects that triggers this check, but it is recommended to check new projects with this flag.
It tests SHA1 and general object sanity, and it does full tracking of the resulting reachability and everything
else. It prints out any corruption it finds (missing or bad objects), and if you use the --unreachable flag it
will also print out objects that exist but that aren't readable from any of the specified head nodes.
So for example
git-fsck-objects --unreachable HEAD $(cat .git/refs/heads/*)
will do quite a lot of verification on the tree. There are a few extra validity tests to be added (make sure that
tree objects are sorted properly etc), but on the whole if "git-fsck-objects" is happy, you do have a valid tree.
Any corrupt objects you will have to find in backups or other archives (i.e., you can just remove them and do an
"rsync" with some other site in the hopes that somebody else has the object you have corrupted).
Of course, "valid tree" doesn't mean that it wasn't generated by some evil person, and the end result might be
crap. git is a revision tracking system, not a quality assurance system ;)
EXTRACTED DIAGNOSTICS
expect dangling commits - potential heads - due to lack of head information
You haven't specified any nodes as heads so it won't be possible to differentiate between un-parented commits
and root nodes.
missing sha1 directory <dir>
The directory holding the sha1 objects is missing.
unreachable <type> <object>
The <type> object <object>, isn't actually referred to directly or indirectly in any of the trees or commits
seen. This can mean that there's another root node that you're not specifying or that the tree is corrupt. If
you haven't missed a root node then you might as well delete unreachable nodes since they can't be used.
missing <type> <object>
The <type> object <object>, is referred to but isn't present in the database.
dangling <type> <object>
The <type> object <object>, is present in the database but never directly used. A dangling commit could be a
root node.
warning: git-fsck-objects: tree <tree> has full pathnames in it
And it shouldn't...
sha1 mismatch <object>
The database has an object who's sha1 doesn't match the database value. This indicates a serious data
integrity problem.
ENVIRONMENT VARIABLES
GIT_OBJECT_DIRECTORY
used to specify the object database root (usually $GIT_DIR/objects)
GIT_INDEX_FILE
used to specify the index file of the index
GIT_ALTERNATE_OBJECT_DIRECTORIES
used to specify additional object database roots (usually unset)
DOCUMENTATION
Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
GIT
Part of the git(7) suite
CATEGORY