git add 错误，git add不了文件

git 错误

git命令行模式，输入git add 命令出现如下错误

fatal: Unable to create ‘C:/Users/cp/Documents/GitHub/first/.git/index.lock’: File exists.

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.

HEAD，指到当前我的远程github learngit仓库的master分支，如图想git add 当前的更改（对应图中未提交的更改），git add出现如上错误。

提示存在 index.lock 文件，进入C:/Users/cp/Documents/GitHub/first/.git,删除掉index.lock文件，即可解决