升级参考文章：
https://www.cnblogs.com/nmap/p/10779658.html（centos7 升级openssh到openssh-8.0p1版本）
https://blog.csdn.net/qq_38000902/article/details/80969769（Linux Centos7 OpenSSH版本低导致的安全漏洞 升级OpenSSH和OpenSSl来修复漏洞）
https://jingyan.baidu.com/article/08b6a5916ecc5214a9092244.html（最全CentOS7升级OpenSSH方案）
https://openbsd.hk/pub/OpenBSD/OpenSSH/portable/（ssh下载）
https://blog.csdn.net/weixin_34301307/article/details/89692821（记一次离线RHEL7，Openssh7.7p1的RPM方式升级）
https://www.cnblogs.com/xun0523/p/9804953.html（Centos 6.x 升级openssh版本）
自己碰到的问题：
1、缺少gcc
[root@credit_elsearch zlib-1.2.8]# gcc -v
bash: gcc: command not found...
[root@credit_elsearch zlib-1.2.8]# ./configure
Checking for gcc...
Compiler error reporting is too harsh for ./configure (perhaps remove -Werror).
** ./configure aborting.
下载参考：http://rpmfind.net/linux/rpm2html/search.php?query=ntp
rpm -ivh mpfr-3.1.1-4.el7.x86_64.rpm
rpm -ivh libmpc-1.0.1-3.el7.x86_64.rpm
rpm -ivh kernel-headers-3.10.0-123.el7.x86_64.rpm
rpm -ivh glibc-headers-2.17-55.el7.x86_64.rpm
rpm -ivh glibc-devel-2.17-55.el7.x86_64.rpm
rpm -ivh cpp-4.8.2-16.el7.x86_64.rpm
rpm -ivh gcc-4.8.2-16.el7.x86_64.rpm
2、编译安装openssl报错：POD document had syntax errors at /usr/bin/pod2man line 69. make: *** [install_docs]
错误如下：
| 1 2 3 4 5 6 7 |
|
解决方法：
执行：
rm -f /usr/bin/pod2man 重新编译安装即可。
3、openssh安装好默认是不执行sshd_config文件的
vim /etc/init.d/sshd
在 ‘$SSHD $OPTIONS && success || failure’这一行上面加上一行 ‘OPTIONS="-f /etc/ssh/sshd_config"’
保存退出
4、root用户无法登陆
解决：vim /etc/ssh/sshd_config
#PermitRootLogin prohibit-password改成PermitRootLogin yes
5、升级openssh后Xshell、SecureCRT等工具无法连接xftp和不能上传文件
解决：vim /etc/ssh/sshd_config
# override default of no subsystems
#Subsystem sftp /usr/local/openssh/libexec/sftp-server改成下面那句
Subsystem sftp internal-sftp
6、PAM报错
Jul 1 13:11:19 credit_elsearch sshd[6027]: PAM unable to dlopen(/usr/lib64/security/pam_stack.so): /usr/lib64/security/pam_stack.so: cannot open shared object file: No such file or directory
Jul 1 13:11:19 credit_elsearch sshd[6027]: PAM adding faulty module: /usr/lib64/security/pam_stack.so
Jul 1 13:11:19 credit_elsearch sshd[6027]: Failed password for root from 10.23.181.28 port 60094 ssh2
经过排查发现是ssh rpm 升级后会修改/etc/pam.d/sshd 文件，如下：
#%PAM-1.0
auth required pam_stack.so service=system-auth
account required pam_nologin.so
account required pam_stack.so service=system-auth
password required pam_stack.so service=system-auth
session required pam_stack.so service=system-auth
修改为之前的即可。修改后的文件如下：
#%PAM-1.0
auth required pam_sepermit.so
auth include password-auth
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 optional pam_keyinit.so force revoke
session include password-auth7、编译和安装openssl时出错，POD document had syntax errors
installing man1/smime.1
smime.pod around line 272： Expected text after =item， not a number
smime.pod around line 276： Expected text after =item， not a number
smime.pod around line 280： Expected text after =item， not a number
smime.pod around line 285： Expected text after =item， not a number
smime.pod around line 289： Expected text after =item， not a number
POD document had syntax errors at /usr/bin/pod2man line 71.
make： *** ［install_docs］ 错误 255
原因分析：这是由于OpenSSL 1.0.1e 与 perl5.18 不兼容。
解决方法：
1、有人验证 安装perl 5.16 可以兼容，安排低版本perl 5.16可以解决问题。
2、删除 pod2man文件：
sudo rm /usr/bin/pod2man