本文摘自PHP中文网，作者零下一度，侵删。
1.下载最新的openssh包
2.升级openssh之前要先打开服务器telnet，通过telnet登录服务器，因为升级过程中会导致ssh暂时不能用
打开linux telnet服务：
查看telnet是否已经安装：
rpm -qa|grep telnet
telnet-0.17-48.el6.x86_64
telnet-server-0.17-48.el6.x86_64
如果没有安装，通过yum安装
[root@leotest ~]# yum install telnet
[root@leotest ~]# yum install telnet-server
启动telnet服务：
编辑telnet文件，将disable改成no
[root@leotest xinetd.d]# vi /etc/xinetd.d/telnet
# default: on
# description: The telnet server serves telnet sessions; it uses \
# unencrypted username/password pairs for authentication.
service telnet
{
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/sbin/in.telnetd
log_on_failure += USERID
disable = no
}
重启xinetd服务：
service xinetd restart
or:
/etc/rc.d/init.d/xinetd restart
通过telnet连接服务器：
[c:\~]$ telnet 192.168.5.5
Connecting to 192.168.5.5:23...
Connection established.
To escape to local shell, press 'Ctrl+Alt+]'.
Red Hat Enterprise Linux Server release 6.8 (Santiago)
Kernel 2.6.32-642.el6.x86_64 on an x86_64
login: test
Password:
[test@leotest ~]$
由于默认telnet只能连接普通用户，所以需要登录普通用户之后跳转到root用户
3.备份原openssh相关文件：
cp /usr/sbin/sshd /usr/sbin/sshd.bak
cp /etc/ssh/ssh_config /etc/ssh/ssh_config.bak
cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak
cp /etc/ssh/moduli /etc/ssh/moduli.bak
Note:删除掉下面三个文件，否则安装的时候会报错：
/etc/ssh/ssh_config already exists, install will not overwrite
/etc/ssh/sshd_config already exists, install will not overwrite
/etc/ssh/moduli already exists, install will not overwrite
rm /etc/ssh/ssh_config -fr
rm /etc/ssh/sshd_config -fr
rm /etc/ssh/moduli -fr
yum install pam-devel
yum install zlib-devel
yum install openssl-devel
4.解压并安装openssh
[root@leotest softs]# tar -zxvf openssh-7.4p1.tar.gz
[root@leotest softs]# ls
openssh-7.4p1 openssh-7.4p1.tar.gz openssh-7.4p1-vs-openbsd.diff.gz
[root@leotest softs]# cd openssh-7.4p1
[root@leotest openssh-7.4p1]#./configure --prefix=/usr/local/openssh --sysconfdir=/etc/ssh --with-pam --with-md5-passwords --mandir=/usr/share/man
### configure: error: *** zlib.h missing ?C please install first or check config.log
#yum install zlib-devel
###configure: error: *** Can’t find recent OpenSSL libcrypto (see config.log for details) ***
#yum install openssl openssl-devel
重新编译：
重新编译前要先清理之前的编译信息：
make clean
ldconfig
[root@leotest openssh-7.4p1]# ./configure --prefix=/usr/local/openssh --sysconfdir=/etc/ssh --with-pam --with-md5-passwords --mandir=/usr/share/man
OpenSSH has been configured with the following options:
User binaries: /usr/bin
System binaries: /usr/sbin
Configuration files: /etc/ssh
Askpass program: /usr/libexec/ssh-askpass
Manual pages: /usr/share/man/manX
PID file: /var/run
Privilege separation chroot path: /var/empty
sshd default user PATH: /usr/bin:/bin:/usr/sbin:/sbin
Manpage format: doc
PAM support: no
OSF SIA support: no
KerberosV support: no
SELinux support: no
Smartcard support:
S/KEY support: no
MD5 password support: no
libedit support: no
Solaris process contract support: no
Solaris project support: no
Solaris privilege support: no
IP address in $DISPLAY hack: no
Translate v4 in v6 hack: yes
BSD Auth support: no
Random number source: OpenSSL internal ONLY
Privsep sandbox style: rlimit
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:
Linker flags: -Wl,-z,relro -Wl,-z,now -Wl,-z,noexecstack -fstack-protector-all -pie
Libraries: -lcrypto -lrt -ldl -lutil -lz -lcrypt -lresolv
make && make install
/etc/init.d/sshd restart
5.覆盖旧的文件
cp -p /softs/openssh-7.4p1/contrib/redhat/sshd.init /etc/init.d/sshd
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