git, nagios and hooks, corrupted git repo

itemprop="text">

Background

We're
using nagios to monitor our infrastructure. We don't have the nagios configs under
version control at the moment, and there are two of us that manage nagios configuration.
As such, I'm working to get our nagios config into a central git repo, using some hooks
to do syntax checking and then if the configs look good, make them "active". I'm using
rel="noreferrer">this guy's post as a starting
point.

The general workflow I'm trying to
implement is:

1. Edit local
   git repo of nagios config. Add edited files, commit
   locally.


2. git push origin master
   to the remote repo.


3. Push is intercepted by the
   pre-receive hook, which takes the files, moves them to a temporary directory on the
   server, and runs them through the nagios syntax
   checker.



4. If the syntax checker passes, accept
   the push, then use the post-commit hook to git pull the new
   code into the live nagios configuration directory and then restart
   nagios.


5. If the syntax checker fails, reject the push,
   showing the nagios syntax error to the
   user.

I'm running into an
odd behavior, though, when I reject a git push due to syntax errors in the nagios
config. What I expect to happen is that if I reject the hook, the attempted push should
leave the repository just how it was, untouched. That doesn't appear to be the case,
though. Below are the details of what I'm
seeing:

Problem

I
edit the nagios config locally, intentionally including a syntax error, add, then commit
locally:

host:nagios
            erik$ vi nagios.cfg
host:nagios erik$ git add nagios.cfg
host:nagios
            erik$ git commit -m "syntax error"
[master da71aed] syntax error
 1
            files changed, 1 insertions(+), 0
            deletions(-)

Now I
push those changes to the master repo. This will be rejected due to the syntax
error:

host:nagios erik$ git push
            origin master

Counting objects: 5, done.
Delta
            compression using up to 8 threads.
Compressing objects: 100% (2/2),
            done.
Writing objects: 100% (3/3), 12.74 KiB, done.
Total 3 (delta
            1), reused 2 (delta 1)
remote: Previous HEAD position was 3ddc880... removed
            syntax error
remote: HEAD is now at da71aed... syntax error
remote:
            Nagios Config Check Exit Status: 254
remote: Your configs did not parse
            correctly, there was an error. Output
            follows.
remote:

remote: Nagios Core
            3.2.3
remote: Copyright (c) 2009-2010 Nagios Core Development Team and
            Community Contributors
remote: Copyright (c) 1999-2009 Ethan
            Galstad
remote: Last Modified: 10-03-2010
remote: License:
            GPL
remote:
remote: Website: http://www.nagios.org
remote:
            Reading configuration data...
remote: Error in configuration file
            '/tmp/nagiosworkdir/nagios.cfg' - Line 23 (NULL value)
remote: Error
            processing main config
            file!

remote:
remote:
remote:
remote:
            ***> One or more problems was encountered while processing the config
            files...
remote:
remote: Check your configuration file(s) to ensure
            that they contain valid
remote: directives and data defintions. If you are
            upgrading from a previous
remote: version of Nagios, you should be aware that
            some variables/definitions
remote: may have been removed or modified in this
            version. Make sure to read
remote: the HTML documentation regarding the config
            files, as well as the

remote: 'Whats New' section to find out what
            has changed.
remote:
To
            git@remote-server.example.com:nagios
 ! [remote rejected] master -> master
            (pre-receive hook declined)
error: failed to push some refs to
            'git@remote-server.example.com:nagios'

This
shouldn't have touched the remote repo, but it did. If I
change to another local temp directory and try to clone the repo, I
get:

host:temp erik$ git clone
            git@remote-server.example.com:nagios

Cloning into
            nagios...
remote: Counting objects: 30, done.
remote: Compressing
            objects: 100% (29/29), done.
remote: Total 30 (delta 12), reused 0 (delta
            0)
Receiving objects: 100% (30/30), 29.81 KiB, done.
Resolving
            deltas: 100% (12/12), done.
error: Trying to write ref HEAD with nonexistant
            object da71aedfde2e0469288acd9e45bb8b57a6e5a7b3
fatal: Cannot update the ref
            'HEAD'.

Now
I go back to the original work directory, fix the syntax error, add, commit, and
push:

host:nagios erik$ vi
            nagios.cfg
host:nagios erik$ git add nagios.cfg
host:nagios erik$
            git commit -m "removing syntax error, push should succeed this time"
[master
            f147ded] removing syntax error, push should succeed this time
 1 files
            changed, 0 insertions(+), 2 deletions(-)
host:nagios erik$ git push origin
            master
Counting objects: 6, done.
Delta compression using up to 8
            threads.

Compressing objects: 100% (4/4), done.
Writing
            objects: 100% (4/4), 487 bytes, done.
Total 4 (delta 2), reused 0 (delta
            0)
remote: Previous HEAD position was 4c80d45... syntax
            error
remote: HEAD is now at f147ded... removing syntax error, push should
            succeed this time
remote: Nagios Config Check Exit Status: 0
remote:
            Your configs look good and parsed correctly.
To
            git@remote-server.example.com:nagios
 3ddc880..f147ded master ->
            master

At
this point, the repository is fine, and I'm able to change to a temporary directory and
clone the repo again:

host:temp
            erik$ git clone git@remote-server.example.com:nagios
Cloning into
            nagios...
remote: Counting objects: 34, done.
remote: Compressing
            objects: 100% (33/33), done.
remote: Total 34 (delta 14), reused 0 (delta
            0)
Receiving objects: 100% (34/34), 30.22 KiB, done.
Resolving
            deltas: 100% (14/14),
            done.

Here
is the rel="noreferrer">pre-receive hook I'm
using.

I'm using git v1.7.5.4 on the client, and
v1.7.2.3 on the server.

So, to the
question: why is the repository being left in an
inconsistent state when I reject the push? Is something awry with my git hook or perhaps
my understanding of git is lacking?

class="post-text" itemprop="text">

class="normal">Answer

You're
doing:

export
            GIT_WORK_TREE=/tmp/nagiosworkdir
/usr/bin/git checkout -f
            $NEW_SHA1

in your
hook. Although it's not touching your usual working-copy it is
updating references in the git-dir (specifically the HEAD
reference), as shown in your
error:

...
remote: HEAD
            is now at da71aed... syntax
            error
...

Your
hook is doing exit 1 to reject the update, but it's not
(re)resetting the HEAD reference after
failure.

I think you need to update the failure
branch in your hook like
so:

...
if [
            "$NAGIOS_CHECK_STATUS" -ne 0 ]
 then
 echo "Your configs did not
            parse correctly, there was an error. Output follows."
 cat
            $GIT_WORK_TREE/check.out

 /usr/bin/git reset --hard $OLD_SHA1 #
            <-- Add This
 exit 1
else

            ...