一、防止ssh升级失败连接不上，首先开启telnet服务：
安装xinetd和telnet-server
yum -y install xinetd yum -y install telnet-server
配置开机启动
systemctl enable xinetd.service systemctl enable telnet.socket
启动服务
systemctl start telnet.socket systemctl start xinetd
查看端口,看到23端口已打开
netstat -tunlp|grep 23
开启防火墙允许访问23端口(没开防火墙跳过此步骤)
firewall-cmd --add-port=23/tcp --permanent firewall-cmd --reload
默认root无法远程访问，修改/etc/securetty
vi /etc/securetty #在末尾添加 pts/0 pts/1 pts/2 pts/3 pts/4
测试用telnet连接
telnet 192.168.139.101 23 输入用户 输入密码
二、开始升级
1、openssh源码包下载：
wget https://cdn.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-8.9p1.tar.gz
2、备份ssh相关文件：
cd /usr/bin/ mkdir bak.1021 cp -arf scp sftp ssh ssh-add ssh-agent ssh-keygen ssh-keyscan bak.1021/ mv /usr/libexec/openssh/sftp-server bak.1021/ ls bak.1021/
cd /usr/sbin/ mkdir bak.1021 cp -arf sshd bak.1021/ ls bak.1021/
3、备份ssh配置文件：
mv /etc/ssh /etc/ssh.1021
4、安装依赖：
yum -y install gcc yum -y install zlib yum -y install zlib-devel yum -y install openssl-devel yum -y install pam-devel
5、编译安装：
tar xf openssh-8.9p1.tar.gz cd openssh-8.9p1 ./configure --prefix=/usr/local/openssh --sysconfdir=/etc/ssh --with-pam --with-zlib --with-md5-passwords --with-tcp-wrappers --without-openssl-header-check make make install
6、修改sshd配置文件：
vi /etc/ssh/sshd_config
修改以下选项
PermitRootLogin yes SyslogFacility AUTHPRIV Subsystem sftp /usr/libexec/openssh/sftp-server
7、拷贝新版本ssh：
cp -arf /usr/local/openssh/sbin/sshd /usr/sbin/ cp -arf /usr/local/openssh/bin/* /usr/bin/
8、#拷贝新版本sftp-server
cp /usr/local/openssh/libexec/sftp-server /usr/libexec/openssh/
9、恢复秘钥文件
cp -arf /etc/ssh.1021/ssh_host* /etc/ssh/ chmod 600 /etc/ssh/ssh_host_*_key
10、修改sshd.service文件
sed -i 's/Type=notify/Type=simple/g' /usr/lib/systemd/system/sshd.service
11、重启sshd
systemctl daemon-reload systemctl restart sshd
查看状态
systemctl status sshd netstat -tunlp|grep 22
如果启动失败，查看日志，按住shift g 可以查看最后的日志
journalctl -u sshd
13、查看版本
sshd -V ssh -V
14、最后工作：关闭telnet服务
systemctl disable xinetd.service systemctl disable telnet.socket
systemctl stop telnet.socket systemctl stop xinetd
