Since few time, I use Github for my projects and I have an issue when I want to push commits.
To beginning, I have forked a repository. Then I have cloned the fork (with command line
git clone https://github.com/ ...
git commit -a
fatal: could not read Username for 'https://github.com': No such file or directory
What I had to do was:
git remote rm origin
git remote add origin 'firstname.lastname@example.org:username/repo.git'
Then, I was able to push my changes.