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Trying to determine how quickly a user would be warned of corruption in the object database with git-1.7.4.1, I pulled a one-bit switcheroo:
$ git init repo
Initialized empty Git repository in /tmp/repo/.git/
$ cd repo
$ echo 'very important info' >critical
$ git add critical
$ git commit -m critical
[master (root-commit) c4d6d90] critical
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 critical
$ git ls-tree HEAD
100644 blob 82d423c32c4bb2c52938088e0234db041bf4eaaf critical
$ git show 82d423c32c4bb2c52938088e0234db041bf4eaaf
very important info
$ echo 'Very important info' | git hash-object --stdin -w
81a3797afe76d339db25c0f9c705a6caa47279c2
$ mv .git/objects/81/a3797afe76d339db25c0f9c705a6caa47279c2 \
.git/objects/82/d423c32c4bb2c52938088e0234db041bf4eaaf
Of course, git-fsck notices
$ git fsck error: sha1 mismatch 82d423c32c4bb2c52938088e0234db041bf4eaaf error: 82d423c32c4bb2c52938088e0234db041bf4eaaf: object corrupt or missing missing blob 82d423c32c4bb2c52938088e0234db041bf4eaaf
but git-log is happy with the change
$ git log -p commit c4d6d90467af9ffa94772795d5c5d191228933c1 Author: Greg Bacon <[email protected]> Date: Thu Apr 7 12:20:53 2011 -0500 critical diff --git a/critical b/critical new file mode 100644 index 0000000..82d423c --- /dev/null +++ b/critical @@ -0,0 +1 @@ +Very important info
as is git-checkout.
$ rm critical $ git checkout . $ cat critical Very important info
A specific invocation of git-show reveals the corruption
$ git show 82d423c32c4bb2c52938088e0234db041bf4eaaf error: sha1 mismatch 82d423c32c4bb2c52938088e0234db041bf4eaaf fatal: bad object 82d423c32c4bb2c52938088e0234db041bf4eaaf
but not a broader one.
$ git show commit c4d6d90467af9ffa94772795d5c5d191228933c1 Author: Greg Bacon <[email protected]> Date: Thu Apr 7 12:20:53 2011 -0500 critical diff --git a/critical b/critical new file mode 100644 index 0000000..82d423c --- /dev/null +++ b/critical @@ -0,0 +1 @@ +Very important info
Even git-clone doesn't notice!
$ cd .. $ git clone repo clone Cloning into clone... done. $ cat clone/critical Very important info
What is the full list of specific git command modes (e.g., git show $sha1 should be present but not git show or git show HEAD) that perform integrity checks?
385
There is no central repository. Git has integrity, meaning each file is checked (summed) to be sure there was no bit loss during any file manipulation by git. Each snapshot (also called commit) has a unique identifier.
To check the status, open the git bash, and run the status command on your desired directory. It will run as follows: $ git status.
The git pull command is used to fetch and download content from a remote repository and immediately update the local repository to match that content. Merging remote upstream changes into your local repository is a common task in Git-based collaboration work flows.
Here's how I would go about finding this out, although I'm not going to go through each source file to work out the conditions under which the check is performed. :)
Clone git's source code:
git clone git://git.kernel.org/pub/scm/git/git.git
Check out the version you care about:
cd git
git checkout v1.7.1
Look for that error message:
git grep 'sha1 mismatch'
That leads you to object.c and the parse_object function. Now look for that function:
git grep parse_object
... and go through the 38 files checking the conditions under which that function will be called.
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