[CentOS] How do I get the kernel srpm?

I tried to follow the work flow shown in https://wiki.centos.org/Sources, but 
it does not seem to work:

I did this:

mkdir CentOS
pushd CentOS
git clone https://git.centos.org/git/centos-git-common.git
git clone https://git.centos.org/git/rpms/kernel.git
pushd kernel/
git checkout c6
../centos-git-common/get_sources.sh

And I got the message:

Missing metadata. Please run from inside a sources git repo

What am I missing?
                              

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