git/Documentation/git-fsck.txt
Junio C Hamano f29cd3938d fsck: default to "git fsck --full"
Linus and other git developers from the early days trained their fingers
to type the command, every once in a while even without thinking, to check
the consistency of the repository back when the lower core part of the git
was still being developed.  Developers who wanted to make sure that git
correctly dealt with packfiles could deliberately trigger their creation
and checked them after they were created carefully, but loose objects are
the ones that are written by various commands from random codepaths.  It
made some technical sense to have a mode that checked only loose objects
from the debugging point of view for that reason.

Even for git developers, there no longer is any reason to type "git fsck"
every five minutes these days, worried that some newly created objects
might be corrupt due to recent change to git.

The reason we did not make "--full" the default is probably we trust our
filesystems a bit too much.  At least, we trusted filesystems more than we
trusted the lower core part of git that was under development.

Once a packfile is created and we always use it read-only, there didn't
seem to be much point in suspecting that the underlying filesystems or
disks may corrupt them in such a way that is not caught by the SHA-1
checksum over the entire packfile and per object checksum.  That trust in
the filesystems might have been a good tradeoff between fsck performance
and reliability on platforms git was initially developed on and for, but
it may not be true anymore as we run on many more platforms these days.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2009-10-20 12:11:39 -07:00

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git-fsck(1)
===========
NAME
----
git-fsck - Verifies the connectivity and validity of the objects in the database
SYNOPSIS
--------
[verse]
'git fsck' [--tags] [--root] [--unreachable] [--cache] [--no-reflogs]
[--[no-]full] [--strict] [--verbose] [--lost-found] [<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' defaults to using the
index file, all SHA1 references in .git/refs/*, and all reflogs (unless
--no-reflogs is given) 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.
--no-reflogs::
Do not consider commits that are referenced only by an
entry in a reflog to be reachable. This option is meant
only to search for commits that used to be in a ref, but
now aren't, but are still in that corresponding reflog.
--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. This is now default; you can turn it off
with --no-full.
--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.
--verbose::
Be chatty.
--lost-found::
Write dangling objects into .git/lost-found/commit/ or
.git/lost-found/other/, depending on type. If the object is
a blob, the contents are written into the file, rather than
its object name.
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 --unreachable HEAD \
$(git for-each-ref --format="%(objectname)" 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' 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: 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)
Author
------
Written by Linus Torvalds <torvalds@osdl.org>
Documentation
--------------
Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
GIT
---
Part of the linkgit:git[1] suite