I create the key using the command ssh-keygen
ssh-keygen -t rsa -b 4096 -C "email@example.com"
The key is written to the file ~/.ssh/id_rsa. During the day I have been using them (for git push github.com on site). And the next day I find out that you can not push. It turned out that the file ~/.ssh/id_rsa changed (there was a long text, but in the end someone has cut it by half). The public key is also changed.
How could this happen?
This has been going on three virtual machines that I create on c9.io.