I have run gitlabhq rails server on virtual machine, following 1-6 steps from this tutorial https://github.com/gitlabhq/gitlab-recipes/blob/master/install/centos/README.md a
GitLab by default marks master
branch as protected
(See part Protecting your code
in https://about.gitlab.com/2014/11/26/keeping-your-code-protected/ why). If so in your case, then this can help:
Open your project > Settings > Repository and go to "Protected branches", find "master" branch into the list and click "Unprotect" and try again.
via https://gitlab.com/gitlab-com/support-forum/issues/40
For version 8.11 and above how-to here: https://docs.gitlab.com/ee/user/project/protected_branches.html#restricting-push-and-merge-access-to-certain-users