In git, it is possible in the default configuration for anyone with commit permission to really mess things up. Someone can do a force push and wipe out everyone else’s commits.
Stop all force pushes
The bare authoritative repository can be configured to deny non-fast-forward commits such as this even when forced. An overview of this is in Git Configuration in the git book. The main settings are:
git config --system receive.denyNonFastForwards true
git config --system receive.denyDeletes true
Note that --system here will write to the /etc/gitconfig file.
Stop some force pushes
For individual branches, there is a pre-receive hook available here on Github.
I have also heard that it is possible to prevent specific users from force pushing using a pre-receive hook on the server.
Note that it is not possible to add the above on Github – the workaround is to let only a limited number of people commit, and have everyone else use pull requests.
Maybe stop some force pushes
Another option is to add a pre-push hook to run on the client, which can be used for projects on Github. This is not strictly enforceable, since a user could remove it and still do a forced push, but it can prevent accidental pushing to master, and would be a decent safety net for people new to git to make sure they can’t accidentally break something too much. Some good-looking instructions for setting it up are in the blog post Do not allow force push to master.
Fast-Forward Only Pull Requests on GitHub
Just email GitHub and ask for them, according to @domenic:
If you want ff-only merges on GitHub, email support@github.com to ask for that feature. I just did! https://t.co/ZaOwwu87jc
— Domenic Denicola (@domenic) June 18, 2014