Xshell意外关闭可能会出现这种问题，如遇如下错误可解决：

Connecting to 47.106.80.28:22…
Connection established.
To escape to local shell, press ‘Ctrl+Alt+]’.

Socket error Event: 32 Error: 10053.
Connection closing…Socket close.

Connection closed by foreign host.

Disconnected from remote host(47.106.80.28) at 21:34:21.

Type `help’ to learn how to use Xshell prompt.

由于意外关闭，linux 中秘钥的权限会跟着更改，至于原因暂时未知，解决办法如下：

可通过网页控制台进入系统，服务器供应商都会提供对应的网页控制端，可登陆系统，网页登录不受影响。
执行如下代码：
//进入到ssh秘钥目录
cd /etc/ssh
//更改秘钥权限
chmod 400 ./*
重启sshd
sudo systemctl restart sshd

xshell再次连接，成功！