1.If no other git process is currently running, this probably means a git process crashed in this repository earlier. Make sure no other git process is running and remove the file manually to continue.
解决方法：
rm -f ./.git/index.lock
2.git push 提示 “更新被拒绝，因为您当前分支的最新提交落后于其对应的远程分支”
解决方法：
A.本地已存在项目,需要先获取远端更新并与本地合并,再git push,具体操作如下:
git remote add origin https://github.com/username/Hello-World.git
git fetch origin //获取远程更新
git merge origin/master //把更新的内容合并到本地分支
B.下面方式也可以解决此问题
git pull origin master
