linux常用的服务--SSH以及ssh公钥认证

一、ssh（secure shell）安装

SSH默认情况下已经安装了，包装包的名称是openssh，使用源码包安装的方法是

[root@localhost logs]# yum install openssh

………………………………

Downloading Packages:
(1/4): openssh-5.3p1-84.1.el6.x86 | 236 kB     00:00     
(2/4): openssh-askpass-5.3p1-84.1 |  53 kB     00:00     
(3/4): openssh-clients-5.3p1-84.1 | 355 kB     00:00     
(4/4): openssh-server-5.3p1-84.1. | 299 kB     00:00 

……………………

二、ssh相关的文件详解

1、 /etc/ssh/sshd_config   ssh 服务的主配置文件，基本上所有的ssh相关设定都在这里

# This is the sshd server system-wide configuration file.  See
# sshd_config(5) 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 22       -----sshd服务默认的端口22，为了安全考虑建议修改成其它端口

#AddressFamily any
ListenAddress 192.168.1.1  -------------监听的主机，只监听来自192.168.1.1的ssh连接
#ListenAddress ::
# Disable legacy (protocol version 1) support in the server for new
# installations. In future the default will change to require explicit
# activation of protocol 1
Protocol 2           ----------------ssh的协议版本，这里是2

# HostKey for protocol version 1
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
#HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key

# Lifetime and size of ephemeral version 1 server key
#KeyRegenerationInterval 1h                -----------每个一个小时重新建立一次连接，这里未开启
#ServerKeyBits 1024       -----------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（/var/log/secure）
#LogLevel INFO

# Authentication:
#LoginGraceTime 2m
#PermitRootLogin yes        -----------是否允许root登陆，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就不接受其联机
#MaxAuthTries 6               --------------最多root尝试6次连接
#MaxSessions 10

#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
#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rhosts认证，为了安全一定设置为否
# similar for protocol version 2
#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
# 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 bypassthe 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 yes      -----------启用pam模块
# 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
#PrintMotd yes       ---------登陆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，任何一端死后，马上断开
#UseLogin no
#UsePrivilegeSeparation yes   -------------使用者的权限设定
#PermitUserEnvironment no
#PidFile /var/run/sshd.pid
#MaxStartups 10     ----------最大联机画面
#PermitTunnel no
#ChrootDirectory none
# override default of no subsystems

Subsystem       sftp    /usr/libexec/openssh/sftp-server         ----------  sftp服务的设置

++++++++++++以上是sshd服务端+++++++下面是客户端++++++++

2、/etc/ssh/ssh_config    -------ssh客户端配置文件

# This is the ssh client system-wide configuration file.  See
# ssh_config(5) 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.
# 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
#   CheckHostIP yes    -------------是否验证ip
#   AddressFamily any
#   ConnectTimeout 0   ----------连接超时时间
#   StrictHostKeyChecking ask
#   IdentityFile ~/.ssh/identity
#   IdentityFile ~/.ssh/id_rsa
#   IdentityFile ~/.ssh/id_dsa
#   Port 22          ------------连接远程主机的端口
#   Protocol 2,1  -----------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,[email protected],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

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

3、~/.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

三、ssh服务控制命令

启动ssh服务： service sshd start

关闭ssh服务：service sshdstop

重启ssh服务： service sshd restart

 [root@localhost softs]# netstat -anpt | grep sshd     ----------查看sshd的22端口是否打开

tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN      2854/sshd 

ssh命令常用的参数

-l  指定用户；   -p指定端口号；   -X开启x协议转发

[root@localhost softs]# ssh [email protected]
The authenticity of host '192.168.254.46 (192.168.254.46)' can't be established.
RSA key fingerprint is 18:5f:3e:08:d0:a7:f1:93:f9:34:63:41:31:24:2a:02.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.254.46' (RSA) to the list of known hosts.
[email protected]'s password:           #输入密码

Last login: Wed Oct 23 10:20:19 2013 from 192.168.254.152      -----登陆成功

[root@localhost ~]# exit -------断开ssh连接
logout
Connection to 192.168.254.46 closed.

[root@localhost softs]# ssh -p 22 -l root 192.168.254.46   #P默认为22，可以省略
[email protected]'s password: 

[root@localhost softs]# ssh 192.168.254.46
[email protected]'s password:

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

四、ssh的公钥认证

1.生成密钥文件

[root@localhost ~]# lsb_release -a   -------先看一下我的linux版本
LSB Version:    :core-3.1-ia32:core-3.1-noarch:graphics-3.1-ia32:graphics-3.1-noarch
Distributor ID: RedHatEnterpriseServer
Description:    Red Hat Enterprise Linux Server release 5.5 (Tikanga)
Release:        5.5
Codename:       Tikanga

[root@localhost ~]# ssh-keygen -t rsa         #生成密钥对
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):         #输入私钥文件的名称，直接回车使用默认名称
Enter passphrase (empty for no passphrase):    #输入密钥文件的密码，直接回车不设置密码
Enter same passphrase again:                          #再次输入密码确认
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
d3:41:dd:41:56:a2:ca:7a:81:9a:64:74:d7:df:32:9e [email protected]

[root@localhost ~]# ll /root/.ssh/
总计 12
-rw------- 1 root root 1675 10-23 10:28 id_rsa      -------生成的私钥
-rw-r--r-- 1 root root  408 10-23 10:28 id_rsa.pub  ------生成的公钥
-rw-r--r-- 1 root root  396 10-23 10:20 known_hosts ------登陆者的信息

2、将公钥复制到远程主机

[root@localhost ~]# scp ~/.ssh/id_rsa.pub [email protected]:~/.ssh/authorized_keys

------将公钥复制到远程服务器指定的目录下，并且重命名为authorized_keys。scp是openssh自带的工具。

[email protected]'s password:      --------输入远程主机的密码
id_rsa.pub                 100%  408     0.4KB/s   00:00 

3、登录到远程主机

[root@localhost ~]# ssh 192.168.254.46
[email protected]'s password:

查看该主机的系统版本

[root@localhost ~]# cat /proc/version 
Linux version 2.6.32-71.el6.x86_64 ([email protected]) (gcc version 4.4.4 20100726 (Red Hat 4.4.4-13) (GCC) ) #1 SMP Fri May 20 03:51:51 BST 2011
[root@localhost ~]# 

然后再该主机上同样生成公钥

[root@localhost ~]# 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.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
6b:35:ba:70:2d:06:ee:3e:80:37:7b:ee:9c:1f:c1:2e [email protected]
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|                 |
|                 |
|       .         |
|   .  . S o      |
|  . +. o * .     |
|   . +E X .      |
|    .ooB +       |
|     =Boo        |
+-----------------+

  将公钥传到192.168.254.153上面

[root@localhost ~]# ssh-copy-id -i ~/.ssh/id_rsa.pub [email protected]   ======另外一种远程传公钥的方法
The authenticity of host '192.168.254.153 (192.168.254.153)' can't be established.
RSA key fingerprint is 4d:24:b3:e8:82:11:bf:e1:a0:0c:45:27:57:8e:a1:c8.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.254.153' (RSA) to the list of known hosts.
[email protected]'s password:     ----------------输入192.168.254.153的密码

Now try logging into the machine, with "ssh '[email protected]'", and check in:

  .ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

[root@localhost ~]# ssh [email protected]
Last login: Wed Oct 23 09:55:54 2013 from 192.168.254.152    ----------不用输密码可以直接登陆了

五 、ssh客户端的使用

ssh 客户端的命令主要包括ssh ，scp和sftp

1、ssh的使用 

ssh [email protected] 以root身份 远程登录远程主机

2、scp命令

scp命令可以用来通过安全加密的连接在机器之间进行文件的传输，与rcp相似。它传文件的一般语法为

scp localfile username@hostip:/newfilename

localfile  本地文件名称，username 远程主机用户名 hostip远程主机的ip地址

举例：scp  /var/log/httpd/access.log  [email protected]:/var/log/

把本地/var/log/httpd/下的access.log文件传到远程主机对应的/var/log/下面

3、sftp命令

sftp工具可以用来打开一次安全互动的ftp对话。与ftp类似，但是sftp使用安全加密的连接，一般语法为

sftp [email protected]

[root@localhost .ssh]# sftp 192.168.254.153   sftp登陆，因为我交换了公钥，所以无需密码认证
Connecting to 192.168.254.153...
sftp> ls  ---------查看有哪些文件 
Desktop                                                 
anaconda-ks.cfg                                         
glibc-2.7-2.i386.rpm                                    
glibc-common-2.7-2.i386 .rpm                            
glibc-devel-2.7-2.i386.rpm                              
glibc-headers-2.7-2.i386.rpm                            
index.php                                               
install.log                                             
install.log.syslog                                      
jdk1.7.0                                                
mbox                                                    
my.cnf                                                  
phpMyAdmin-4.0.8-all-languages.tar.gz                   
sftp> get my.cnf           我随便下载了一个文件
Fetching /root/my.cnf to my.cnf    
/root/my.cnf          100% 4920     4.8KB/s   00:00    
sftp> quit

六、访问控制

/etc/host.allow和/etc/hosts.deny

这两个文件时控制远程访问设置的，通过该设置可以允许或者拒绝某个ip或者ip段访问linux的某项服务。

[root@localhost .ssh]# vi /etc/hosts.allow

sshd:192.168.0.*:allow  允许该网段访问

sshd:192.168.1.15:allow  允许该ip地址访问

[root@localhost .ssh]# vi /etc/hosts.deny

sshd:all:deny   -------表示拒绝所有的sshd远程连接

当/etc/hosts.deny 跟/etc/hosts.allow冲突时会以哪个为准？这里有个规则

首先检查hosts.allow文件，若找到相关的策略则允许访问，否则继续检查hosts.deny ，若找到相关的策略则拒绝访问；如果两个文件中都没有匹配的策略则允许访问；如果二者冲突时以hosts.allow为准。

注意：如果这两个文件配置修改了，必须要重启service xinetd服务才能生效