Seems there is an issue floating around when a user tries to push on their GitLab CentOS installation. There are two ways one can push to a git repo. Using their username:password through http and using their ssh key without the need of a password. For example:

git push https://centos.local/axil/git.git master

will prompt for the GitLab username:password

whereas

git push git@centos.local:axil/git.git master

will push to the repo without the need of a password just using the ssh key I uploaded using the GitLab interface.

Note: Pushing via ssh usually requires that you have set up properly your .ssh/config for the user you are pushing from. Mine entry for example looks like:

Host centos.local
  User axil
  Hostname centos.local
  PreferredAuthentications publickey
  IdentityFile /home/axil/.ssh/id_rsa

If you have installed GitLab on CentOS/RHEL, you may not be able to push via ssh and the reason is the restrictions SELinux has on /home/git/.ssh/ directory. In order to fix this problem, simply run as root:

restorecron -Rv /home/git/.ssh/

You can read more here.

The above fix has already taken its way upstream in the CentOS guide at the gitlab-recipes repo. If you find any other issues you are welcome to submit them in the bug tracker.