If another person has pushed to the same branch as you, Git won't be able to push your changes:
$ git push origin master > To https://hostname/USERNAME/REPOSITORY.git > ! [rejected] master -> master (non-fast-forward) > error: failed to push some refs to 'https://hostname/USERNAME/REPOSITORY.git' > To prevent you from losing history, non-fast-forward updates were rejected > Merge the remote changes (e.g. 'git pull') before pushing again. See the > 'Note about fast-forwards' section of 'git push --help' for details.
You can fix this by fetching and merging the changes made on the remote branch with the changes that you have made locally:
$ git fetch origin # Fetches updates made to an online repository $ git merge origin YOUR_BRANCH_NAME # Merges updates made online with your local work
Or, you can simply use
git pull to perform both commands at once:
$ git pull origin YOUR_BRANCH_NAME # Grabs online updates and merges them with your local work