一、升级前准备工作
安装openssh过程需gcc，zlib-devel,openssl-devel,等编译环境，如果通过rpm包来安装，需要解决各种依赖包，故配置本地yum源解决依赖问题。
1. 配置本地yum源
[root@localhost cdrom]# mount /dev/cdrom /mnt/cdrom/ #挂载关盘
[root@localhost ~]# cd /etc/yum.repos.d/
[root@localhost yum.repos.d]# vi CentOS-Media.repo #配置yum源环境
[c6-media]
name=CentOS-$releasever - Media
baseurl=file:///mnt/cdrom #指定光盘路径
gpgcheck=1
enabled=1
gpgkey=file:///mnt/cdrom/RPM-GPG-KEY-CentOS-6
2. 安装telnet服务
安装telnet服务，防止升级openssh失败，不能远程登录操作系统（安装过程略，可以通过rpm或yum安装）
3.上传 openssh-7.5p1.tar.gz
二、升级openssh
1.升级前备份openssh配置
[root@localhost chu]# mv /etc/ssh /etc/ssh.old
[root@localhost chu]# mv /etc/init.d/sshd /etc/init.d/sshd.old
2.卸载当前openssh
[root@localhost chu]# rpm -qa |grep openssh
openssh-5.3p1-117.el6.x86_64
openssh-server-5.3p1-117.el6.x86_64
[root@localhost chu]# rpm -e --nodeps openssh-5.3p1-117.el6.x86_64
[root@localhost chu]# rpm -e --nodeps openssh-server-5.3p1-117.el6.x86_64
error reading information on service sshd: No such file or directory
error: %preun(openssh-server-5.3p1-117.el6.x86_64) scriptlet failed, exit status 1
卸载 openssh-5.3p1-117.el6.x86_64报错
解决办法：
[root@localhost chu]# rpm -e --noscripts openssh-server-5.3p1-117.el6.x86_64
3.源码编译
在编译源码过程中会多次出现报错问题，可以通过日志查看缺少编译环境，在安装对应包。
1）第一次编译
[root@localhost openssh-7.5p1]# ./configure --prefix=/usr --sysconfdir=/etc/ssh
checking for gcc... no
checking for cc... no
checking for cl.exe... no
configure: error: in `/home/packgates/ssh_pack/openssh-7.5p1':
configure: error: no acceptable C compiler found in $PATH
See `config.log' for more details
报错：缺少gcc
2）安装gcc编译器
[root@localhost openssh-7.5p1]# yum install gcc
3）第二次编译
[root@localhost openssh-7.5p1]# ./configure --prefix=/usr --sysconfdir=/etc/ssh
checking for zlib.h... no
configure: error: *** zlib.h missing - please install first or check config.log ***
报错：缺少zlib-devel
4）安装zlib-devel
[root@localhost openssh-7.5p1]# yum install zlib-devel
5）第三次编译
[root@localhost openssh-7.5p1]# ./configure --prefix=/usr --sysconfdir=/etc/ssh
checking openssl/opensslv.h presence... no
checking for openssl/opensslv.h... no
configure: error: *** OpenSSL headers missing - please install first or check config.log ***
报错：没有openssl-devel
6）安装openssl-devel
[root@localhost openssh-7.5p1]# yum install openssl-devel
7）第四次编译
[root@localhost openssh-7.5p1]# ./configure --prefix=/usr --sysconfdir=/etc/ssh
......
Host: x86_64-pc-linux-gnu
Compiler: gcc
Compiler flags: -g -O2 -Wall -Wpointer-arith -Wuninitialized -Wsign-compare -Wformat-security -Wno-pointer-sign -fno-strict-aliasing -D_FORTIFY_SOURCE=2 -ftrapv -fno-builtin-memset -fstack-protector-all -fPIE
Preprocessor flags: -D_XOPEN_SOURCE=600 -D_BSD_SOURCE -D_DEFAULT_SOURCE
Linker flags: -Wl,-z,relro -Wl,-z,now -Wl,-z,noexecstack -fstack-protector-all -pie
Libraries: -lcrypto -lrt -ldl -lutil -lz -lcrypt -lresolv
没有报错
8）最后一步 make && make install
[root@localhost openssh-7.5p1]# make && make install
......
ssh-keygen: generating new host keys: RSA DSA ECDSA ED25519
/usr/sbin/sshd -t -f /etc/ssh/sshd_config
检查安装结果：
[root@localhost openssh-7.5p1]# ssh -V
OpenSSH_7.5p1, OpenSSL 1.0.1e-fips 11 Feb 2013
安装成功。
4.配置ssh服务
1.复制启动文件到/etc/init.d/目录下并命名sshd
[root@localhost openssh-7.5p1]# cp contrib/redhat/sshd.init /etc/init.d/sshd
2.ssh加入到开机启动
[root@localhost openssh-7.5p1]# chkconfig --add sshd #ssh加入到开机启动
[root@localhost openssh-7.5p1]# chkconfig --list sshd #检查ssh开机启动状态
sshd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
3.允许root登录ssh
[root@localhost openssh-7.5p1]# vi /etc/ssh/sshd_config
新加一行PermitRootLogin yes
4.重启ssh服务
[root@localhost openssh-7.5p1]# service sshd restart
Stopping sshd: [ OK ]
/sbin/restorecon: lstat(/etc/ssh/ssh_host_key.pub) failed: No such file or directory
Starting sshd: [ OK ]
最后测试，能ssh登录到操作系统，至此升级openssh完成。
其他
在安装openssh前，本想先卸载旧的openssl,安装新的openssl，结果卸载后yum不能使用，只要又重新openssl,过程见如下。
卸载openssl后踩的坑，卸载后yum安装报错。
[root@localhost ssh_pack]# rpm -e --nodeps openssl-1.0.1e-48.el6.x86
[root@localhost ssh_pack]# yum install gcc
There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:
libssl.so.10: cannot open shared object file: No such file or directory
Please install a package which provides this module, or
verify that the module is installed correctly.
It's possible that the above module doesn't match the
current version of Python, which is:
2.6.6 (r266:84292, Jul 23 2015, 15:22:56)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-11)]
If you cannot solve this problem yourself, please go to
the yum faq at:
http://yum.baseurl.org/wiki/Faq
挂载光盘，重新安装openssl
[root@localhost Packages]# rpm -ivh openssl-devel-1.0.1e-48.el6.x86_64.rpm openssl-1.0.1e-48.el6.x86_64.rpm --nodeps --force
ssh登录问题
问题1：crt登录报错（提示信息：Password authentication faild. Please verify that the username and password are correct.）
重启sshd服务后，crt能登录，但是重启过程中报如下错误。
[root@localhost chu]# service sshd restart
Stopping sshd: [ OK ]
/sbin/restorecon: lstat(/etc/ssh/ssh_host_key.pub) failed: No such file or directory
Starting sshd: [ OK ]
解决办法：
[root@localhost ssh]# vi /etc/init.d/sshd <<-------启动脚本
# /sbin/restorecon /etc/ssh/ssh_host_key.pub
官方通告（http://www.openssh.com/txt/release-6.9），openssh从7.0以后版本不在对version1.x支持了，相应的RSA1算法也不再支持，编译openssh源码后不会再/etc/ssh目录下生成ssh_host_key.pub文件。在启动脚本中注释掉/etc/ssh/ssh_host_key.pub即可。
问题2：crt不能登录，重启ssh服务，crt登录恢复，重启操作系统后，必须重启ssh服务，ssh登录恢复。
检查开机启动，ssh服务状态，都是正常的
[root@localhost ssh]# chkconfig --list sshd
sshd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
[root@localhost ssh]# service sshd status
sshd (pid 1309) is running...
[root@localhost ssh]# netstat -npl |grep 22
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1309/sshd
tcp 0 0 :::22 :::* LISTEN 1309/sshd
1.通过在本地ssh root@127.0.0.1,报/root/.ssh/known_hosts错误，清空known_hosts文件内容，ssh登录恢复正常。
2.关闭selinux
总结：用ssh登录服务器，ssh会把每个访问服务器的公钥(public key)都记录在/root/.ssh/known_hosts文件中，当下次访问相同服务器时，ssh就会核对公钥。升级openssh后，以前的公钥信息还存在，登录时就会不匹配，因此需要清空以前的公钥，重新生成新的公钥才能重新登录。
