查看原版本：ssh -V
查找并删除原装软件：
rpm -qa |grep openssh
for i in $(rpm -qa |grep openssh);do rpm -e $i --nodeps;done
依赖包安装：
yum install -y pam-devel rpm-build openssl-devel gcc lrzsz
#下载地址：
https://cdn.openbsd.org/pub/OpenBSD/OpenSSH/portable/
wget https://cdn.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-8.4p1.tar.gz.asc
tar xf openssh-8.4p1.tar.gz
cd openssh-8.4p1
./configure --prefix=/usr --sysconfdir=/etc/ssh --with-md5-passwords--with-pam--with-tcp-wrappers --with-ssl-dir=/usr/local/ssl --without-hardening
rm -rf /etc/ssh #这步很关键
make && make install
替换启动脚本并设置开机自启：
cp contrib/redhat/sshd.init /etc/init.d/sshd
chkconfig --add sshd
chkconfig sshd on
sed -i "32a PermitRootLogin yes" /etc/ssh/sshd_config
systemctl restart sshd
ssh -V
重启之后如果root远程连接不上（尽管密码是对的依然提示错误）解决办法：关闭防火墙和selinux
systemctl stop firewalld
setenforce 0