! [rejected] master -> master (fetch first)

Solution 1:

The answer is there, git is telling you to fetch first.

Probably somebody else has pushed to master already, and your commit is behind. Therefore you have to fetch, merge the changeset, and then you'll be able to push again.

If you don't (or even worse, if you force it by using the --force option), you can mess up the commit history.

EDIT: I get into more detail about the last point, since a guy here just gave the Very Bad Advice of using the --force option.

As git is a DVCS, ideally many other developers are working on the same project as you, using the same repository (or a fork of it). If you overwrite forcefully with your changeset, your repository will mismatch other people's, because "you rewrote history". You will make other people unhappy and the repository will suffer. Probably a kitten in the world will cry, too.

TL;DR

1. If you want to solve, fetch first (and then merge).
2. If you want to hack, use the --force option.

You asked for the former, though. Go for 1) always, even if you will always use git by yourself, because it is a good practice.

Solution 2:

try:

git fetch origin master
git merge origin master

After to wrote this code I received other error: (non-fast-forward)

I write this code:

git fetch origin master:tmp
git rebase tmp
git push origin HEAD:master
git branch -D tmp

And resolved my problem

Solution 3:

You should use git pull, that´s command do a git fetch and next do the git merge.

If you use a git push origin master --force command, you may have problems in the future.

Solution 4:

pull is always the right approach but one exception could be when you are trying to convert a none-Git file system to a Github repository. There you would have to force the first commit in.

git init
git add README.md
git add .
git commit -m "first commit"
git remote add origin https://github.com/userName/repoName.git
git push --force origin master