首先看一下实验环境:
[root@localhost ~]# cat /proc/version #ip 192.168.254.130
Linux version 2.6.32-431.el6.x86_64 (mockbuild@c6b8.bsys.dev.centos.org) (gcc version 4.4.7 20120313 (Red Hat 4.4.7-4) (GCC) ) #1 SMP Fri Nov 22 03:15:09 UTC 2013
[root@wulaoer ~]# cat /proc/version #ip 192.168.254.131
Linux version 2.6.32-431.el6.x86_64 (mockbuild@c6b8.bsys.dev.centos.org) (gcc version 4.4.7 20120313 (Red Hat 4.4.7-4) (GCC) ) #1 SMP Fri Nov 22 03:15:09 UTC 2013
wlof@wlof-virtual-machine:~$ sudo cat /proc/version #192.168.254.129
[sudo] wlof 的密码：
Linux version 4.2.0-16-generic (buildd@lcy01-07) (gcc version 5.2.1 20151003 (Ubuntu 5.2.1-21ubuntu2) ) #19-Ubuntu SMP Thu Oct 8 15:35:06 UTC 2015
两台centos和一台ubuntu，两台centos版本相同，为了区分我把每台的用户用红色进行区分。如果你的是刚刚安装的系统那就需要你安装ssh，centos直接yum -y install ssh 如果是ubuntu的话就用sudo apt-get install openssh-server很简单的，一条命令执行就可以了。
第一：密钥生成
[root@wulaoer ~]# ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa. #私钥文件
Your public key has been saved in /root/.ssh/id_rsa.pub. #公钥文件
The key fingerprint is:
8e:5f:78:ca:fc:79:cc:e0:c7:18:2a:31:2f:0a:8d:40 root@wulaoer
The key's randomart image is:
+--[ RSA 2048]----+
| |
| |
| E |
|. |
|. S |
| . o oo .o |
| o . .+oooB |
| . o+o+o.* |
| .. o=.oo |
+-----------------+
[root@wulaoer ~]# cd /root/.ssh/ #如果是ubuntu的话是家目录下的用户名下的.ssh目录下。
[root@wulaoer .ssh]# ls
id_rsa id_rsa.pub
第二：可以直接在本地修改公钥文件名也可以在传送的过程修改，这个根据自己习惯。
[root@wulaoer .ssh]# ll
总用量 12
-rw-------. 1 root root 1675 5月 12 23:10 id_rsa
-rw-r--r--. 1 root root 394 5月 12 23:10 id_rsa.pub
-rw-r--r--. 1 root root 397 5月 12 20:13 known_hosts
[root@wulaoer .ssh]# mv id_rsa.pub authorized_keys #或者
[root@wulaoer .ssh]# scp -r authorized_keys 192.168.254.130:/root/.ssh/
root@192.168.254.130's password:
authorized_keys 100% 394 0.4KB/s 00:00
第三：测试直接登录看一下需不需要使用密码。
[root@wulaoer .ssh]# ssh 192.168.254.130
Last login: Fri May 13 00:28:12 2016 from 192.168.254.131
[root@localhost ~]#
这里需要注意下，主机名已经发送变化，说明已经登录成功。
一台机器名wulaoe和一台ubuntu同时免密码登录localhost，wulaoer已经设置好了，下面是设置ubuntu。
wlof@wlof-virtual-machine:~$ cd /home/wlof/.ssh/ #这里的wolf是我的用户名下的家目录
wlof@wlof-virtual-machine:~/.ssh$ ls
known_hosts
wlof@wlof-virtual-machine:~/.ssh$ ssh-keygen -t rsa #如果这里要是加sudo的话认证的用户就是root了，要看一下认证文件的路径
Generating public/private rsa key pair.
Enter file in which to save the key (/home/wlof/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/wlof/.ssh/id_rsa. #私钥文件路径
Your public key has been saved in /home/wlof/.ssh/id_rsa.pub. #公钥文件路径
The key fingerprint is:
SHA256:fE+oB2MQ4GFwWa4Misx8BsTTPRBtcztHWgkoUA/G78A wlof@wlof-virtual-machine
The key's randomart image is:
+---[RSA 2048]----+
|.o*BX++.. . |
|.o.B+X o + |
| .+ =.* = |
|=..E o * . . |
|o+ o= S o . |
| o . . = o |
| . . . |
| . |
| |
+----[SHA256]-----+
wlof@wlof-virtual-machine:~/.ssh$ ls
id_rsa id_rsa.pub known_hosts
ssh验证测试
wlof@wlof-virtual-machine:~/.ssh$ scp -r id_rsa.pub root@192.168.254.130:/root/.ssh/authorized_keys #在这里要注意必须要在连接的IP前加root@，要不系统默认会用当前用户名，在这里已经要用追加的方式加进去
root@192.168.254.130's password:
id_rsa.pub 100% 407 0.4KB/s 00:00
wlof@wlof-virtual-machine:~/.ssh$ ssh 192.168.254.130
wlof@192.168.254.130's password: wlof@wlof-virtual-machine:~/.ssh$ ssh root@192.168.254.130
Last login: Fri May 13 00:28:44 2016 from 192.168.254.131
[root@localhost ~]# #主机名已经切换过来，说明登录成功
一台登录多台设置,现在两台centos已经可以相互之间直接登录，现在让ubuntu直接访问两台centos。
首先把ubuntu的公钥复制到两台centos上：
wolf@wolf-virtual-machine:~$ cd /home/wolf/.ssh/
wolf@wolf-virtual-machine:~/.ssh$ ls
id_rsa id_rsa.pub known_hosts
wolf@wolf-virtual-machine:~/.ssh$ scp -r id_rsa.pub root@192.168.254.130:/root/.ssh/authorized_keyss #复制到130上，这里为了和131的公钥区分我在后边多加了一个‘s’
root@192.168.254.130's password:
id_rsa.pub 100% 407 0.4KB/s 00:00
wolf@wolf-virtual-machine:~/.ssh$ scp -r id_rsa.pub root@192.168.254.131:/root/.ssh/authorized_keyss #复制到131上，同上
The authenticity of host '192.168.254.131 (192.168.254.131)' can't be established.
RSA key fingerprint is SHA256:tzpgk9Y/bBiToYmQz3URfDxUKseZ739+kk4TKuDBa5U.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.254.131' (RSA) to the list of known hosts.
root@192.168.254.131's password:
id_rsa.pub
下面就需要在两个centos里设置了，把ubuntu的公钥追加到authorized_keys里，记得是追加不是覆盖。
[root@localhost .ssh]# cat authorized_keyss >> authorized_keys #130上的公钥追加
[root@localhost .ssh]# cat authorized_keys
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAriBZExBXEVl6lzlP5e+ZipchsKQUN9CXQ/oP+tJsfSu8pVt+u1EA8bzNBFg8wSTLqkWIXw9Ko+soPu3cuUzf3ChGWxyutIjYIDbzQ8dm/Ikns6UYGbFAKBmzm+K+mdxKlRvc0DlfM4mBmXwGvp5Mu4bmOU5tBcXxeBACduv4hFwi3fHZ7Kk5WNCuuhHsSmC9udhOTd9eohaY243hYMf7DXssUqR3jltk6Lyl7Cty9/a9Qh/U42/VEEmJ8LaWscRcViLLHv+CCXTlp5s5p9N2HIByHYRQI179hIvZqnmT4GLNpX6vweLWAOqNIragjqUf7PeZxOBhxSQaTNrJJdm71w== root@localhost.localdomain
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDVul880Bj7HmbtObRXODujHNjpYa65dfr+D+k03KL9Woij77jj7oLhpdMk80bINGftCkY612Ou/xCNjPB07UNa1uyoSuXZxGZX4k+f0N4JS9R2qUw9aJKlpciohLrPItXo+Syq7TUOGfi9mB/WoF1aAPdCWYhO8J+J8voFjoAqFDlONzId/xBdELGLBSv6FUG1O2YDVyvHnlrfalxSZvSKdpM/dl8KdogZ8qjDGbLKkkYg7be+na9RRnMt/L8I+Dvww/sxpdZ7JHn23nxkf4Yrln88jcUrJDxYChchD/JBHtV2mFg32w1FPQ2Y3lPSpW6GriQWHc5qeRuGg7JkT1sN wolf@wolf-virtual-machine
在后面查看的时候可以看出是两个公钥了，131上的设置同上，。
[root@wulaoer .ssh]# cat authorized_keyss >> authorized_keys
[root@wulaoer .ssh]# cat authorized_keys
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEArcYpkcSlOgMWzeihri9aFkQC0ggV8s/lhycAo04UuEBhkFVCOk/y3mEXK+16LgHaCekrKyXQakKfRo8/Qdkl87gSFTgU9thA+bMAPf6hwCbHQ4t0Hi+4d0I/rQrI3MTsDNxXGzMfH1w7ZpV6DkYlQ4gcGRGaywyryyuBgypsxsG2ejlZ8Zaa6nv+VYhRe5CzzwC8tCkgCJ6fXGfCP8LWxOPTKKg9AwmIEceuJe0PErrZNADCBmqOGsY/jx6hFqeUNN38QllIta7H9dfogcWsYCEm1PxfDrkBu/eX8qS9qHc5YU64akN1uojPE4Ar5vsT3A083cyiu7Eo91X7T+s1mw== root@localhost.localdomain
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDVul880Bj7HmbtObRXODujHNjpYa65dfr+D+k03KL9Woij77jj7oLhpdMk80bINGftCkY612Ou/xCNjPB07UNa1uyoSuXZxGZX4k+f0N4JS9R2qUw9aJKlpciohLrPItXo+Syq7TUOGfi9mB/WoF1aAPdCWYhO8J+J8voFjoAqFDlONzId/xBdELGLBSv6FUG1O2YDVyvHnlrfalxSZvSKdpM/dl8KdogZ8qjDGbLKkkYg7be+na9RRnMt/L8I+Dvww/sxpdZ7JHn23nxkf4Yrln88jcUrJDxYChchD/JBHtV2mFg32w1FPQ2Y3lPSpW6GriQWHc5qeRuGg7JkT1sN wolf@wolf-virtual-machine
实验结构测试，在ubuntu上直接登录两个不同的centos：
wolf@wolf-virtual-machine:~/.ssh$ ssh root@192.168.254.130 #登录到130上了
Last login: Fri May 13 16:09:15 2016 from 192.168.254.131
[root@localhost ~]# ls
anaconda-ks.cfg install.log Python-2.7.3 rdo-release-liberty-3.noarch.rpm
epel-release-6-8.noarch.rpm install.log.syslog Python-2.7.3.tar.bz2
[root@localhost ~]# exit
logout
Connection to 192.168.254.130 closed.
wolf@wolf-virtual-machine:~/.ssh$ ssh root@192.168.254.131 #登录到131上了
Last login: Sat May 14 00:06:54 2016 from 192.168.254.1
[root@wulaoer ~]# ls
anaconda-ks.cfg install.log install.log.syslog
以下是关于sshd服务端的配置详解ubuntu和centos的文件都一样，这里以centos为例：
[root@localhost ~]# vi /etc/ssh/sshd_config #ssh的主配置文件，基本的ssh相关设置都在这里 # $OpenBSD: sshd_config,v 1.80 // :: djm Exp $ # This is the sshd server system-wide configuration file. See
# sshd_config() for more information. # This sshd was compiled with PATH=/usr/local/bin:/bin:/usr/bin # The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented. Uncommented options change a
# default value. #Port #sshd服务默认的端口22，为了安全建议修改成其它端口
#AddressFamily any
#ListenAddress 0.0.0.0 #监听的主机，可以监听所有的ssh连接
#ListenAddress :: # Disable legacy (protocol version ) support in the server for new
# installations. In future the default will change to require explicit
# activation of protocol
Protocol #ssh的协议版本，这里是2 # HostKey for protocol version
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version
#HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key # Lifetime and size of ephemeral version server key
#KeyRegenerationInterval 1h #每个一个小时重新建立一次连接，这里没有开启
#ServerKeyBits #server key的长度 # Logging
# obsoletes QuietMode and FascistLogging
#SyslogFacility AUTH
SyslogFacility AUTHPRIV #当有人使用ssh登入系统的时候，ssh会记录信息
#LogLevel INFO # Authentication: #LoginGraceTime 2m
#PermitRootLogin yes #是否允许root登录，默认是允许的，建议设置成no
#StrictModes yes #当使用者的host key改变之后，server就不接受其它连接
#MaxAuthTries #最多root尝试6次连接
#MaxSessions #RSAAuthentication yes #是否使用rsa认证，只针对version1
#PubkeyAuthentication yes #是否允许public key，只针对version2
#AuthorizedKeysFile .ssh/authorized_keys #认证文件,客户端连接过来的公钥默认文件命
#AuthorizedKeysCommand none
#AuthorizedKeysCommandRunAs nobody # For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#RhostsRSAAuthentication no #是否仅适用于rhost认证，为了安全一定设置为否
# similar for protocol version
#HostbasedAuthentication no
# Change to yes if you don't trust ~/.ssh/known_hosts for
# RhostsRSAAuthentication and HostbasedAuthentication
#IgnoreUserKnownHosts no #是否忽略掉~/.shosts files中的用户
# Don't read the user's ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes # To disable tunneled clear text passwords, change to no here!
#PasswordAuthentication yes #是否需要密码认证
#PermitEmptyPasswords no #不允许空密码
PasswordAuthentication yes #开启密码认证 # Change to no to disable s/key passwords
#ChallengeResponseAuthentication yes
ChallengeResponseAuthentication no #不挑战任何的密码认证，任何login.conf规定的认证方式，都禁用 # Kerberos options
#KerberosAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no
#KerberosUseKuserok yes # GSSAPI options
#GSSAPIAuthentication no
GSSAPIAuthentication yes
#GSSAPICleanupCredentials yes
GSSAPICleanupCredentials yes
#GSSAPIStrictAcceptorCheck yes
#GSSAPIKeyExchange no # Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication. Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
#UsePAM no #启用pam模块
UsePAM yes # Accept locale-related environment variables #环境变量
AcceptEnv LANG LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE LC_MONETARY LC_MESSAGES
AcceptEnv LC_PAPER LC_NAME LC_ADDRESS LC_TELEPHONE LC_MEASUREMENT
AcceptEnv LC_IDENTIFICATION LC_ALL LANGUAGE
AcceptEnv XMODIFIERS #AllowAgentForwarding yes
#AllowTcpForwarding yes
#GatewayPorts no
#X11Forwarding no
X11Forwarding yes
#X11DisplayOffset
#X11UseLocalhost yes
#PrintMotd yes #登录后是否显示一些默认信息
#PrintLastLog yes #显示上次登录的信息
#TCPKeepAlive yes #ssh server会传keepalive信息给client以此确保两者的联机正常，任何一断死后。马上断开
#UseLogin no
#UsePrivilegeSeparation yes #使用者的权限设定
#PermitUserEnvironment no
#Compression delayed
#ClientAliveInterval
#ClientAliveCountMax
#ShowPatchLevel no
#UseDNS yes
#PidFile /var/run/sshd.pid
#MaxStartups ::
#PermitTunnel no
#ChrootDirectory none # no default banner path
#Banner none # override default of no subsystems
Subsystem sftp /usr/libexec/openssh/sftp-server #sftp服务的设置 # Example of overriding settings on a per-user basis
#Match User anoncvs
# X11Forwarding no
# AllowTcpForwarding no
# ForceCommand cvs server
sshd服务端配置
以下是关于ssh客户端的文件
[root@localhost ~]# vi /etc/ssh/ssh_config # $OpenBSD: ssh_config,v 1.25 // :: djm Exp $ # This is the ssh client system-wide configuration file. See
# ssh_config() for more information. This file provides defaults for
# users, and the values can be changed in per-user configuration files
# or on the command line. # Configuration data is parsed as follows:
# . command line options
# . user-specific file
# . system-wide file
# Any configuration value is only changed the first time it is set.
# Thus, host-specific definitions should be at the beginning of the
# configuration file, and defaults at the end. # Site-wide defaults for some commonly used options. For a comprehensive
# list of available options, their meanings and defaults, please see the
# ssh_config() man page. # Host * #只匹配设定的主机，这里默认是匹配所有的主机
# ForwardAgent no #连接是否经过验证代理
# ForwardX11 no #x11连接是否被自动重定向到安全的通道和显示集；
# RhostsRSAAuthentication no #是否使用rsa算法的基于rhosts的安全验证
# RSAAuthentication yes #是否使用rsa算法验证
# PasswordAuthentication yes #是否使用密码验证
# HostbasedAuthentication no
# GSSAPIAuthentication no
# GSSAPIDelegateCredentials no
# GSSAPIKeyExchange no
# GSSAPITrustDNS no
# BatchMode no
# CheckHostIP yes #是否验证ip
# AddressFamily any
# ConnectTimeout #连接超时时间
# StrictHostKeyChecking ask
# IdentityFile ~/.ssh/identity
# IdentityFile ~/.ssh/id_rsa
# IdentityFile ~/.ssh/id_dsa
# Port #连接远程主机的端口
# Protocol , #采用的协议版本
# Cipher 3des
# Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc
# MACs hmac-md5,hmac-sha1,umac-@openssh.com,hmac-ripemd160
# EscapeChar ~ #设置escape字符
# Tunnel no
# TunnelDevice any:any
# PermitLocalCommand no
# VisualHostKey no
Host *
GSSAPIAuthentication yes
# If this option is set to yes then remote X11 clients will have full access
# to the original X11 display. As virtually no X11 client supports the untrusted
# mode correctly we set this to yes.
ForwardX11Trusted yes
# Send locale-related environment variables
SendEnv LANG LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE LC_MONETARY LC_MESSAGES
SendEnv LC_PAPER LC_NAME LC_ADDRESS LC_TELEPHONE LC_MEASUREMENT
SendEnv LC_IDENTIFICATION LC_ALL LANGUAGE
SendEnv XMODIFIERS
ssh客户端配置文件
最后，说一下~/.ssh/known_hosts文件的作用
ssh 会把每个你访问过的计算机的公钥（public key）都记录到~/.ssh/known_hosts文件中，当你下次访问该计算机时，openss会核对公钥。如果公钥不同，那openssh就会发出警告，避免你收到DNSHijack等攻击