If no other git process is currently running, this probably means a git process crashed in this repo

今天git突然崩溃，崩溃时正在使用创建的新分支。等到重新进入，用git checkout master命令显示

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.

解决方案：

　　把仓库目录里的.git/index.lock文件（文件是隐藏的）删除就可以了。删除index.lock不会影响Git使用。是说index文件被锁住了，但是还有一个index文件要进行操作。

　　一个仓库配有一个.git文件夹，在这个文件夹里面生成了一个index.lock文件，导致index文件不能被操作，所以把index.lock删除就ok