linux常用的服務--SSH以及ssh公鑰認證
一、ssh（secure shell）安裝
SSH默認情況下已經安裝了，包裝包的名稱是openssh，使用源碼包安裝的方法是
[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相關的文件詳解
1、 /etc/ssh/sshd_config ssh 服務的主配置文件，基本上所有的ssh相關設定都在這裡
# 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服務默認的端口22，為了安全考慮建議修改成其它端口
#AddressFamily any
ListenAddress 192.168.1.1 -------------監聽的主機，只監聽來自192.168.1.1的ssh連接
#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的協議版本，這裡是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 -----------每個一個小時重新建立一次連接，這裡未開啟
#ServerKeyBits 1024 -----------server key的長度
# Logging
# obsoletes QuietMode and FascistLogging
#SyslogFacility AUTH
SyslogFacility AUTHPRIV ------------當有人使用ssh登入系統的時候，ssh會記錄信息（/var/log/secure）
#LogLevel INFO
# Authentication:
#LoginGraceTime 2m
#PermitRootLogin yes -----------是否允許root登陸，默認是允許的，建議設置成no
#StrictModes yes -------------當使用者的host key改變之後，server就不接受其聯機
#MaxAuthTries 6 --------------最多root嘗試6次連接
#MaxSessions 10
#RSAAuthentication yes -------------是否使用rsa認證，只針對version1
#PubkeyAuthentication yes ------------是否允許public key，只針對version2
#AuthorizedKeysFile .ssh/authorized_keys -------認證文件
#AuthorizedKeysCommand none
#AuthorizedKeysCommandRunAs nobody
# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#RhostsRSAAuthentication no ---------是否僅適用於rhosts認證，為了安全一定設置為否
# 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中的用戶
# Don't read the user's ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes
# To disable tunneled clear text passwords, change to no here!
#PasswordAuthentication yes --------------是否需要密碼認證
#PermitEmptyPasswords no --------------不允許空密碼
PasswordAuthentication yes -------------開啟密碼認證
# Change to no to disable s/key passwords
#ChallengeResponseAuthentication yes
ChallengeResponseAuthentication no -----------不挑戰任何的密碼認證，任何login.conf規定的認證方式，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 -----------啟用pam模塊
# Accept locale-related environment variables ------------環境變量
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 ---------登陸後是否顯示一些默認信息
#PrintLastLog yes ---------顯示上次登錄的信息
#TCPKeepAlive yes -------ssh server會傳keepalive信息給client以此確保兩者的聯機正常，任何一端死後，馬上斷開
#UseLogin no
#UsePrivilegeSeparation yes -------------使用者的權限設定
#PermitUserEnvironment no
#PidFile /var/run/sshd.pid
#MaxStartups 10 ----------最大聯機畫面
#PermitTunnel no
#ChrootDirectory none
# override default of no subsystems
Subsystem sftp /usr/libexec/openssh/sftp-server ---------- sftp服務的設置
++++++++++++以上是sshd服務端+++++++下面是客戶端++++++++
2、/etc/ssh/ssh_config -------ssh客戶端配置文件
# 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 * -----------只匹配設定的主機，這裡默認是匹配所有的主機
# ForwardAgent no ------------連接是否經過驗證代理
# ForwardX11 no ------------x11連接是否被自動重定向到安全的通道和顯示集；
# RhostsRSAAuthentication no -----是否使用rsa算法的基於rhosts的安全驗證
# RSAAuthentication yes ----------是否使用rsa算法驗證
# PasswordAuthentication yes ----------是否使用密碼驗證
# CheckHostIP yes -------------是否驗證ip
# AddressFamily any
# ConnectTimeout 0 ----------連接超時時間
# StrictHostKeyChecking ask
# IdentityFile ~/.ssh/identity
# IdentityFile ~/.ssh/id_rsa
# IdentityFile ~/.ssh/id_dsa
# Port 22 ------------連接遠程主機的端口
# Protocol 2,1 -----------采用的協議版本
# 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 ~ --------------設置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 會把每個你訪問過的計算機的公鑰（public key）都記錄到~/.ssh/known_hosts文件中，當你下次訪問該計算機時，openss會核對公鑰。如果公鑰不同，那openssh就會發出警告，避免你收到DNSHijack等攻擊
三、ssh服務控制命令
啟動ssh服務： service sshd start
關閉ssh服務：service sshdstop
重啟ssh服務： service sshd restart
[root@localhost softs]# netstat -anpt | grep sshd ----------查看sshd的22端口是否打開
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 2854/sshd
ssh命令常用的參數
-l 指定用戶； -p指定端口號； -X開啟x協議轉發
[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: #輸入密碼
Last login: Wed Oct 23 10:20:19 2013 from 192.168.254.152 -----登陸成功
[root@localhost ~]# exit -------斷開ssh連接
logout
Connection to 192.168.254.46 closed.
[root@localhost softs]# ssh -p 22 -l root 192.168.254.46 #P默認為22，可以省略
[email protected]'s password:
[root@localhost softs]# ssh 192.168.254.46
[email protected]'s password:
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
四、ssh的公鑰認證
1.生成密鑰文件
[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 #生成密鑰對
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): #輸入私鑰文件的名稱，直接回車使用默認名稱
Enter passphrase (empty for no passphrase): #輸入密鑰文件的密碼，直接回車不設置密碼
Enter same passphrase again: #再次輸入密碼確認
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/
總計 12
-rw------- 1 root root 1675 10-23 10:28 id_rsa -------生成的私鑰
-rw-r--r-- 1 root root 408 10-23 10:28 id_rsa.pub ------生成的公鑰
-rw-r--r-- 1 root root 396 10-23 10:20 known_hosts ------登陸者的信息
2、將公鑰復制到遠程主機
[root@localhost ~]# scp ~/.ssh/id_rsa.pub
[email protected]:~/.ssh/authorized_keys
------將公鑰復制到遠程服務器指定的目錄下，並且重命名為authorized_keys。scp是openssh自帶的工具。
[email protected]'s password: --------輸入遠程主機的密碼
id_rsa.pub 100% 408 0.4KB/s 00:00
3、登錄到遠程主機
[root@localhost ~]# ssh 192.168.254.46
[email protected]'s password:
查看該主機的系統版本
[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 ~]#
然後再該主機上同樣生成公鑰
[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 |
+-----------------+
將公鑰傳到192.168.254.153上面
[root@localhost ~]# ssh-copy-id -i ~/.ssh/id_rsa.pub
[email protected] ======另外一種遠程傳公鑰的方法
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: ----------------輸入192.168.254.153的密碼
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 ----------不用輸密碼可以直接登陸了
五 、ssh客戶端的使用
ssh 客戶端的命令主要包括ssh ，scp和sftp
1、ssh的使用
ssh
[email protected] 以root身份 遠程登錄遠程主機
2、scp命令
scp命令可以用來通過安全加密的連接在機器之間進行文件的傳輸，與rcp相似。它傳文件的一般語法為
scp localfile username@hostip:/newfilename
localfile 本地文件名稱，username 遠程主機用戶名 hostip遠程主機的ip地址
舉例：scp /var/log/httpd/access.log
[email protected]:/var/log/
把本地/var/log/httpd/下的access.log文件傳到遠程主機對應的/var/log/下面
3、sftp命令
sftp工具可以用來打開一次安全互動的ftp對話。與ftp類似，但是sftp使用安全加密的連接，一般語法為
sftp
[email protected]
[root@localhost .ssh]# sftp 192.168.254.153 sftp登陸，因為我交換了公鑰，所以無需密碼認證
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 我隨便下載了一個文件
Fetching /root/my.cnf to my.cnf
/root/my.cnf 100% 4920 4.8KB/s 00:00
sftp> quit
六、訪問控制
/etc/host.allow和/etc/hosts.deny
這兩個文件時控制遠程訪問設置的，通過該設置可以允許或者拒絕某個ip或者ip段訪問linux的某項服務。
[root@localhost .ssh]# vi /etc/hosts.allow
sshd:192.168.0.*:allow 允許該網段訪問
sshd:192.168.1.15:allow 允許該ip地址訪問
[root@localhost .ssh]# vi /etc/hosts.deny
sshd:all:deny -------表示拒絕所有的sshd遠程連接
當/etc/hosts.deny 跟/etc/hosts.allow沖突時會以哪個為准？這裡有個規則
首先檢查hosts.allow文件，若找到相關的策略則允許訪問，否則繼續檢查hosts.deny ，若找到相關的策略則拒絕訪問；如果兩個文件中都沒有匹配的策略則允許訪問；如果二者沖突時以hosts.allow為准。
注意：如果這兩個文件配置修改了，必須要重啟service xinetd服務才能生效
