Ubuntu – Import SSH keys for remote server

Why my public key can't be saved as /root/.ssh/myvps.pub?

Your keys can be saved with any name you'd like. However, the ssh client will only automatically search for a few standard names, id_rsa, id_dsa, id_ecdsa, or id_ed25519. If you want to save it under any other name, you need to specify the file name either on the command line:

ssh -i ~/.ssh/myvps root@vps_ip2

or in your ~/.ssh/config file:

Host vps_ip2
    IdentityFile ~/.ssh/myvps
    User root

The bad practice here is that you have your repository in a non-writeable directory. From what you describe, it's even worse and you actually have everyone using the same local git repository! This sort of defeats the entire point of using git in the first place! If any of you screws up the repository, you can't fix it from someone else's local copy. You also can't work at the same time. This is really a very bad setup.

You say you like having to use sudo to make changes. I'm sorry but that just doesn't make sense at all. You control access by controlling what gets merged, not by controlling who can write to the local repository files! Plus, this is a horribly insecure approach: you're giving all of your developers root access to the machine just so they can write their code! I suspect you think this is increasing safety but the truth is that it is doing exactly the opposite.

Tell everyone to run a git clone in their home directories so everyone can have their own, local copy of the code. Next, configure your repository so that it doesn't allow merging without a reviewed pull request. This is something you want anyway.

This will not only let you use git to its fullest extent with everyone having a local copy of the repository which ensures code safety, and allows multiple people to work in parallel, on the same or different branches, it will also have the nice side effect of solving the problem you describe in your question: everyone can now add their own public ssh key to GitHub, store their own private ssh key in $HOME/.ssh/ and be able to push to the repository and open pull requests for the repository owner to review and merge.