flyinweb's blog

1、安装
首先要在存储设备上做好RAID，设置好iSCSI 目标方（target）。
这里主要说明iSCSI initiator的安装。
不同的操作系统对应各自的iSCSI initiator，以Redhat enterprise5为例。到网上下载iscsi-initiator-utils-6.2.0.742-0.5.el5.i386.rpm
# rpm -ivh iscsi-initiator-utils-6.2.0.742-0.5.el5.i386.rpm
在服务器上安装了iSCSI initiator以及iscsiadm
iscsiadm是基于命令行的iscsi管理工具，提供了对iscsi节点、会话、连接以及发现记录的操作。
iscsiadm的使用说明可以查看/usr/share/doc/iscsi-initiator-utils-6.2.0.742/README，也可以运行man iscsiadm或iscsiadm -help

Q. I’ve CentOS 5 server running on Dell hardware. I’m getting following error message in my /var/log/message file (some time message is also shown on console):

Jul 05 12:04:05 dell01 kernel: end_request: I/O error, dev fd0, sector 0
Jul 05 12:04:05 dell01 kernel: Buffer I/O error on device fd0, logical block 0
Jul 05 12:04:18 dell01 kernel: end_request: I/O error, dev fd0, sector 0
Jul 05 12:04:18 dell01 kernel: Buffer I/O error on device fd0, logical block 0
Jul 05 12:04:30 dell01 kernel: end_request: I/O error, dev fd0, sector 0
Jul 05 12:04:42 dell01 kernel: end_request: I/O error, dev fd0, sector 0

What do they mean? How do I fix this problem?

A. This message appears when you don’t have a floppy drive attached to Linux server. Solution is quite simple just disable driver for floppy and reboot the system. You can verify this with the following command (this solution works with RHEL, CentOS, Redhat, Ubuntu/Debian and other Linux distros) :
# lsmod | grep -i floppy
Output:

floppy                 95465  0

Open file called /etc/modprobe.d/blacklist:
# vi /etc/modprobe.d/blacklist
Listing a module (driver name) in this file prevents the hotplug scripts from loading it. Usually that'd be so that some other driver will bind it instead,
no matter which driver happens to get probed first. Sometimes user mode tools can also control driver binding. Append following line:
blacklist floppy
Save and close the file. Now reboot the Linux server:
# reboot

Source from:http://www.cyberciti.biz/faq/linux-end_request-ioerror-dev-fd0-sector0/

简介： 随着Internet技术的迅猛发展，网络技术、性能的不断提高，高可伸缩性、高可用性、可管理性、价格有效性的网络服务技术将成为网络服务技术的主导。各种平台下的技术方案应运而生。本文试图以一篇完整的理论+实践性的文字来介绍如何在优秀的开源操作系统Linux下创建低成本、高性能、高可用的服务集群系统。文中所使用的系统和软件包均为最新版本。希望通过对本文的阅读能使你对如何创建Linux下的集群系统有所帮助。

1.Linux下的解决方案

Linux下的集群系统通常可以分为三类：

1. HA容错集群 (Fail-over Cluster)
   高可用性集群（High available）用于不可间断服务的环境下。提供冗余的容错备份，在主节点失效后，能够立即接管相关资源及继续提供相应服务。
2. 负载均衡集群 (Load Balancing Cluster)
   在应用服务的高负载情况下运用该技术，由多台节点提供高可伸缩的，高负载的服务器组。以保证对外提供良好的服务响应。
3. HPC高性能计算机集群 (High Performance Computing)
   概念并不完全统一，有一定争论，应该理解为并行系统，主要用于科学计算。

我们都知道网易、搜狐等大型门户都有“通行证”的概念，这个通行证系统就是今天讨论的“单点登录系统”。其主要特征是多个站点一个用户中心，一点登陆后其他也自动登录，注销也是。比如我们在126登录了邮箱，再去163.com就是登陆状态。就好比要建一个摩天大楼,打好地基是重点之重.看到SSO的重要性了吧.

下面我简单介绍一下国际一些名气比较大的SSO解决方案:

 Raid and Logical Volume Managers are great, until you lose data.

 Over the weekend I had the worrying experience of losing my LVM settings and potentially all my data… a quick search on the web showed a confusing set of information, much of it for older versions of LVM and therefore rather suspect.

Well, I recovered all my data and it was really quite simple, so I’ve written up what I did in the hope that someone else, in a similar situation, will find it useful. It’s a scary thing, losing the whole hard disk and knowing that, in reality, its all there.

IP Range To CIDR Convertor

// Convert a given Ip range to CIDR notation.

# cat  rangeToCidr

/* rangeToCidr.c - Convert Ip ranges to CIDR */ 
 
/* 
modification history http://snippets.dzone.com/tag/cidr
-------------------- 
01a,17sep08,karn written 
*/ 
 
/* includes */ 
 
#include<stdio.h> 
#include<unistd.h> 
#include<string.h> 
#include<math.h> 
#include<errno.h> 
#include <sys/socket.h> 
#include <netinet/in.h> 
#include <arpa/inet.h> 
 
/* defines */ 
//#define DBG 
#ifdef DBG 
#define DEBUG(x) fprintf(stderr,x) 
#else 
#define DEBUG 
#endif /* DBG */ 
 
#define IP_BINARY_LENGTH 32+1  /* 32 bits ipv4 address +1 for null */ 
#define IP_HEX_LENGTH    10    
#define MAX_CIDR_MASK    32 
#define MAX_CIDR_LEN     18+1   /*255.255.255.255/32*/ 
 
/* Forward declaratopms */ 
void rangeToCidr(uint32_t from ,uint32_t to, 
                 void (callback)(char *cidrNotation)); 
int ipToBin(uint32_t ip , char * pOut); 
 
void printNotation(char *cidrNotation); 
 
/* Globals */ 
 
 
/******************************************************************************* 
* 
* ipToBin - convert an ipv4 address to binary representation  
*           and pads zeros to the beginning of the string if  
*           the length is not 32  
*           (Important for ranges like 10.10.0.1 - 20.20.20.20 ) 
* 
* ip   - ipv4 address on host order 
* pOut - Buffer to store binary. 
* 
* RETURNS: OK or ERROR  
*/ 
 
int ipToBin(uint32_t ip , char * pOut) 
    { 
    char hex[IP_HEX_LENGTH]; 
    int i; 
    int result=0; 
    int len; 
    char pTmp[2]; 
    int tmp; 
    /* 
     * XXX: Could use bit operations instead but was easier to debug 
     */ 
    char binMap[16][5] = {  
                        "0000","0001","0010","0011", "0100", 
                        "0101","0110","0111","1000", "1001", 
                        "1010","1011","1100", "1101","1110","1111", 
                        }; 
    pTmp[1]=0x0; 
    memset(hex,0x0,sizeof(hex)); 
    len=sprintf(hex,"%x",ip); 
 
    for(i=0;i<len;i++) 
        { 
 
        /* Ugly but to use strtol , we need the last byte as null */ 
        pTmp[0]=hex[i]; 
 
        errno = 0; 
        tmp = strtol(pTmp, 0x0, 16); 
 
        /* Should not happen */ 
        if (errno != 0) 
            { 
            memset(pOut,'0',IP_BINARY_LENGTH -1); 
            DEBUG ("strtol failed for hex 0x%s\n",pTmp); 
            return -1; 
            } 
 
        result+=sprintf(pOut+result,"%s",binMap[tmp]); 
        } 
 
        DEBUG("bits %u printed for ip address for hex len %u\n",result,len); 
        /* if length is not 32 , pad the start with zeros*/ 
 
    if(result < IP_BINARY_LENGTH-1) 
        { 
        char pSwap[IP_BINARY_LENGTH]; 
        strncpy(pSwap,pOut,IP_BINARY_LENGTH); 
        memset(pOut,'0',IP_BINARY_LENGTH); 
        strncpy(pOut+IP_BINARY_LENGTH-1-result,pSwap,result); 
        DEBUG("corrected length to 32\n"); 
        } 
 
    else if (result > IP_BINARY_LENGTH-1) 
        return -1; 
 
    /* Success */ 
    return 0; 
    } 
 
/******************************************************************************* 
*  main :  
*  
*  arg1 : Start Ip Address 
*  arg2 : End Ip address 
*/ 
 
int main (int argc,char **argv) 
    { 
    long fromIp, toIp; 
    struct in_addr addr; 
    if(argc !=3 ) 
        { 
        printf("Usage: %s <from> <to>\n",argv[0]); 
        return(0); 
        } 
 
    /* All operation on host order */    
    if (inet_aton(argv[1],&addr) == 0) 
        goto error; 
    fromIp = ntohl(addr.s_addr); 
 
    if (inet_aton(argv[2],&addr) ==0) 
        goto error; 
    toIp = ntohl(addr.s_addr); 
 
    rangeToCidr(fromIp,toIp,printNotation); 
 
    return 0; 
error: 
    printf("Invalid Argument\n"); 
    return -EINVAL; 
    } 
 
 
/******************************************************************************* 
* 
* rangeToCidr - convert an ip Range to CIDR, and call 'callback' to handle 
*               the value.  
* 
* from     - IP Range start address 
* to       - IP Range end address 
* callback - Callback function to handle cidr. 
* RETURNS: OK or ERROR  
*/ 
 
void rangeToCidr(uint32_t from ,uint32_t to, 
                 void (callback)(char *cidrNotation)) 
    { 
    int     cidrStart = 0; 
    int     cidrEnd = MAX_CIDR_MASK - 1; 
    long    newfrom; 
    long    mask; 
    char    fromIp[IP_BINARY_LENGTH]; 
    char    toIp[IP_BINARY_LENGTH]; 
    struct  in_addr addr; 
    char    cidrNotation[MAX_CIDR_LEN]; 
 
    memset (fromIp,0x0,sizeof(fromIp)); 
    memset (toIp,0x0,sizeof(toIp)); 
 
    if ( ipToBin(from,fromIp) != 0 )  
        return; 
    if ( ipToBin(to,toIp) != 0 ) 
        return; 
 
    DEBUG ("from %lu to %lu\n", from,to); 
    DEBUG("from %s\n",fromIp); 
    DEBUG("to   %s\n",toIp); 
 
    if(from < to ) 
        { 
 
        /* Compare the from and to address ranges to get the first 
         * point of difference 
         */ 
 
        while(fromIp[cidrStart]==toIp[cidrStart]) 
            cidrStart ++; 
        cidrStart = 32 - cidrStart -1 ; 
        DEBUG("cidrStart is %u\n",cidrStart); 
 
        /* Starting from the found point of difference make all bits on the  
         * right side zero  
         */ 
 
        newfrom = from >> cidrStart +1  << cidrStart +1 ;         
 
        /* Starting from the end iterate reverse direction to find  
         * cidrEnd 
         */  
        while( fromIp[cidrEnd] == '0' && toIp[cidrEnd] == '1') 
            cidrEnd --; 
 
        cidrEnd = MAX_CIDR_MASK - 1 - cidrEnd; 
        DEBUG("cidrEnd is %u\n",cidrEnd); 
 
        if(cidrEnd <= cidrStart) 
            { 
            /*  
             * Make all the bit-shifted bits equal to 1, for 
             * iteration # 1. 
             */ 
             
            mask = pow (2, cidrStart ) - 1; 
            DEBUG("it1 is %lu \n",newfrom | mask ); 
            rangeToCidr (from , newfrom | mask, callback); 
            DEBUG("it2 is %lu \n",newfrom | 1 << cidrStart); 
            rangeToCidr (newfrom | 1 <<  cidrStart ,to ,callback); 
            } 
        else 
            { 
            addr.s_addr = htonl(newfrom); 
            sprintf(cidrNotation,"%s/%d",  
                    inet_ntoa(addr), MAX_CIDR_MASK-cidrEnd); 
            if (callback != NULL) 
                callback(cidrNotation); 
            } 
        } 
 
    else 
        { 
        addr.s_addr = htonl(from); 
        sprintf(cidrNotation,"%s/%d",inet_ntoa(addr),MAX_CIDR_MASK); 
        if(callback != NULL) 
            callback(cidrNotation); 
        } 
    } 
 
/******************************************************************************* 
* 
* printNotation - This is an example callback function to handle cidr notation.  
* 
* RETURNS: 
*/ 
 
void printNotation(char *cidrNotation) 
{ 
    printf("%s\n",cidrNotation); 
} 

编译：

# gcc rangeToCidr.c -lm -o rang2cidr

Perl版本：

#!/usr/bin/perl -w 
# range2cidr.pl 
 
use Net::CIDR; 
use Net::CIDR ':all'; 
 
if (@ARGV == 0) { 
  die "Usage Example: $0 192.168.0.0-192.168.255.255 \n"; 
} 
 
print join("\n", Net::CIDR::range2cidr("$ARGV[0]")) . "\n"; 

I'm new to networking and need help with network settings. I'm looking for a tool for calculating available host address ranges with CIDR using Linux command prompt. How do I use subnet calculator under Linux or UNIX?