Re: Overwriting bare repositories' master

[Sylvain Beucler <beuc@gnu.org>]

On Sun, Oct 29, 2006 at 01:59:42PM -0800, Junio C Hamano wrote:
> Sylvain Beucler <beuc@gnu.org> writes:
> 
> > I tried and I found something that doesn't seem to follow the
> > documentation:
> >
> > repo_one$ git push Beuc@cvs.sv.gnu.org:/srv/git/sources/administration.git \
> >   master:refs/heads/master
> > # [OK]
> > repo_two$ git push --force Beuc@cvs.sv.gnu.org:/srv/git/administration.git \
> >   +refs/heads/master:refs/heads/master
> > updating 'refs/heads/master'
> >   from ee3bda653dfabaf0f78f2a9977abec180f2b19dc
> >   to   c9a726b610bafc82142a16af80b83d28375ca619
> > Generating pack...
> > Done counting 0 objects.
> > Total 0, written 0 (delta 0), reused 0 (delta 0)
> > Unpacking 0 objects
> > error: denying non-fast forward; you should pull first
> >
> > From man git-push:
> > "If the optional plus + is used, the remote ref is updated even if it
> > does not result in a fast forward update."
> >
> > This also makes one wonder how the 'pu' git branch is updated.
> >
> > One the one hand, this means that sysadmin intervention is required to
> > reset such a repository, which is bad. One the other hand, this is
> > also a security because users cannot erase history, even if there a
> > cron job to prune&pack the git repositories, which is good.
> >
> > Is this by design? Or should it work?
> 
> I suspect (because I cannot see your .git/config in the
> repository; which would say "[core] sharedrepository = 1" if my
> suspicion is correct) that this is fairly new heavyhanded safety
> valve added by the list around mid September, with this:
> 
>     commit 11031d7e9f34f6a20ff4a4bd4fa3e5e3c0024a57
>     Author: Johannes Schindelin <Johannes.Schindelin@gmx.de>
>     Date:   Thu Sep 21 01:07:54 2006 +0200
> 
>         add receive.denyNonFastforwards config variable
> 
>         If receive.denyNonFastforwards is set to true,
>         git-receive-pack will deny non fast-forwards, i.e. forced
>         updates. Most notably, a push to a repository which has that
>         flag set will fail.
> 
>         As a first user, 'git-init-db --shared' sets this flag,
>         since in a shared setup, you are most unlikely to want
>         forced pushes to succeed.
> 
> The reasoning is exactly as you guessed.
> 
> I think the intention of the patch is that the repository
> administrators are expected to either (1) adjust the
> non-fast-forwarding branch to fast-forward (by reset --hard to
> an ancestor of what you are trying to push into), (2)
> temporarily disable the safety value by editing .git/config, or
> (3) instead of pushing into it, force fetching into it from the
> repository machine.
> 
> It is doing what it was designed to do.  It is a different issue
> if the design is good, but rewinding the public branch is not
> something even a repository administrator should take lightly
> and not expected to happen often (except in cases like yours
> where the administrator is tipping his toe into the water), so I
> think overall the current behaviour is an acceptable balance
> between safety and convenience.
> 
> My public repository is not shared (only I can push into it) so
> this is a non-issue for my 'pu' branch.


You perfectly guessed the situation.

Setting denyNonFastforwards=false allowed the forced push to succeed.
For reference the config file was
(http://cvs.sv.gnu.org/r/test.git/config):
[core]
	repositoryformatversion = 0
	filemode = true
	sharedrepository = 1
[receive]
	denyNonFastforwards = true

This sounds like a sound design :)

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