centos7 telnet 登录升级ssh

https://www.cnblogs.com/missinglihua/articles/7234667.html

ssh升级

http://blog.51cto.com/lidongfeng/1932891

ssh server端口转发

https://www.jb51.net/article/107751.htm

加入系统服务

[Unit]
Description=OpenSSH server daemon
Documentation=man:sshd(8) man:sshd_config(5)
After=network.target

[Service]
ExecStart=/usr/sbin/sshd

[Install]
WantedBy=multi-user.target