1. 前置条件

首先安装telnet保证额外的连接，另外注意一旦卸载openssh那么久无法重新连接了，所以不能断开连接

yum install telnet* -y && \

systemctl start telnet.socket && \

systemctl enable telnet.socket && \

mv /etc/securetty /etc/securetty.bak && \

systemctl disable --now firewalld && \

yum remove -y openssl && \

yum remove -y openssh

2. 安装软件包

注意顺序不能乱因为存在依赖关系，否则会导致无法安装缺少依赖

rpm -ivh openssl-1.1.1w-1.el7.x86_64.rpm --nodeps && \

rpm -ivh openssh-9.5p1-1.el7.x86_64.rpm && \

rpm -ivh openssh-server-9.5p1-1.el7.x86_64.rpm && \

rpm -ivh openssh-clients-9.5p1-1.el7.x86_64.rpm && \

yum localinstall -y *.rpm

3. 配置软件

3.1 配置秘钥

生成一个秘钥，并且设置秘钥权限，如果不设置会导致sshd启动后无法读取秘钥，进而导致进程无法启动

##生成秘钥并且赋予权限

ssh-keygen -t dsa -f /etc/ssh/ssh_host_dsa_key -N "" && \

chmod 600 /etc/ssh/ssh_host_*_key

3.2 修改配置文件

这里查询出的配置项必须保持一致，可以在此基础上增加其他的功能

[root@localhost ~]# grep ^[A-Z] /etc/ssh/sshd_config

PermitRootLogin yes

PasswordAuthentication yes

UsePAM yes

Subsystem sftp /usr/libexec/openssh/sftp-server

3.3 修复pam的sshd模块

##替换内容重启

vi /etc/pam.d/sshd

文件内容如下—一行都不能少，如果少会导致ssh服务正常，却无法登录

#%PAM-1.0

auth required pam_sepermit.so

auth substack password-auth

auth include postlogin

# Used with polkit to reauthorize users in remote sessions

-auth optional pam_reauthorize.so prepare

account required pam_nologin.so

account include password-auth

password include password-auth

# pam_selinux.so close should be the first session rule

session required pam_selinux.so close

session required pam_loginuid.so

# pam_selinux.so open should only be followed by sessions to be executed in the user context

session required pam_selinux.so open env_params

session required pam_namespace.so

session optional pam_keyinit.so force revoke

session include password-auth

session include postlogin

# Used with polkit to reauthorize users in remote sessions

-session optional pam_reauthorize.so prepare

3.4 重启服务

直接重启即可，如果遇到问题可以查看服务运行状态

systemctl daemon-reload && \

systemctl restart sshd

4 查看结果

[root@localhost ~]# cat /etc/redhat-release

CentOS Linux release 7.4.1708 (Core) //查看操作系统版本

[root@localhost ~]# ssh -V

OpenSSH_9.5p1, OpenSSL 1.1.1w 11 Sep 2023 //查看SSH和SSL版本

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