我正在使用 ssh 密钥，但有一天突然停止工作。这就是我尝试克隆时得到的结果。此外，known_hosts 文件中没有任何内容。我该怎么办？
sarthak@Sarthak:~/.ssh$ git clone git@github.com:sarthmit/Andrew-Ng-ML-solutions.git
Cloning into 'Andrew-Ng-ML-solutions'...
ssh_exchange_identification: Connection closed by remote host
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
sarthak@Sarthak:~/Desktop/Web Scraping$ ssh -vvv git@github.com
OpenSSH_7.2p2 Ubuntu-4ubuntu2.2, OpenSSL 1.0.2g 1 Mar 2016
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: resolving "github.com" port 22
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to github.com [192.30.253.113] port 22.
debug1: Connection …