Centos5.5下建立无盘系统

 1.          简介

本文介绍通过VMware建立Centos无盘系统的测试过程

基本实现原理：在Image Server上建立dhcp,tftp,nfs服务，然后启动diskless client—>dhcp获得IP—>tftp获取内核文件vmlinuz(可引导的、压缩的内核), initrd.img(用来临时的引导硬件到实际内核vmlinuz能够接管并继续引导的状态)--->通过nfsroot(Mounting the root filesystem via NFS)来挂载根分区到Image Server上实现无盘系统

 

2.          通过Yum 安装dhcp,tftp,nfs ,busybox-anaconda(用于redhat的安装管理程序一个单一的binary,包含大量系统指令,包括shell), system-config-netboot-cmd(用于命令行下建立无盘环境)

l  yum –y install dhcp tftp nfs-utils nfs-utils-lib busybox-anaconda system-config-netboot-cmd

 

3.          修改dhcp配置文件并启动

l  vi /etc/dhcpd.conf   allow bootp; allow booting;   ddns-update-style interim; ignore client-updates;   subnet 192.168.159.0 netmask 255.255.255.0 { range 192.168.159.200 192.168.159.220; default-lease-time 21600; max-lease-time 43200; option routers 192.168.159.2; option domain-name-servers 192.168.159.2; option subnet-mask 255.255.255.0; option domain-name "pwrd.com"; option time-offset -18000; filename "linux-install/pxelinux.0";  #需要指定pxelinux.0(PXE启动引导文件)的位置，默认在/tftpboot下 next-server 192.168.159.120;      #指定tftp的IP地址   #可以指定diskless client的IP地址 host test4 {     hardware ethernet 00:0c:29:a3:86:c3;     fixed-address 192.168.159.130;   } }   #启动dhcp, 如有报错可以查看/var/log/messages 中的log l  /etc/init.d/dhcpd start

 

4.          修改tftp配置文件并启动

l  vi /etc/xinetd.d/tftp   service tftp {         socket_type             = dgram         protocol                = udp         wait                    = yes         user                    = root         server                  = /usr/sbin/in.tftpd         server_args             = -s /tftpboot  #指定tftp下载的主目录         disable                 = no      #从yes改为no         per_source              = 11         cps                     = 100 2         flags                   = IPv4 }   #启动tftp, 如有报错可以查看/var/log/messages 中的log l  /etc/init.d/xinetd start

 

5.         建立diskless client所需要的root目录,并同步系统文件到diskless root目录中,在根目录下排除不需要的目录即可,比如/proc /sys

l  mkdir -p /diskless/centos/test4/root/   #192.168.159.120为本机,image server l  rsync -v -a -e ssh --exclude='/proc/*' --exclude='/sys/*' --exclude='/mnt/*' 192.168.159.120:/ /diskless/centos/test4/root/

 

6.          修改NFS配置文件,指定挂载目录,并启动NFS服务

#snapshot 是为了那些每一个diskless client都需要读写的部分，例如/var/log/messages等 l  vi /etc/exports /diskless/centos/test4/root/             *(rw,sync,no_root_squash,no_all_squash) /diskless/centos/test4/root/snapshot/     *(rw,sync,no_root_squash,no_all_squash)   #启动portmap 和NFS, 如有报错可以查看/var/log/messages 中的log /etc/init.d/portmap start /etc/init.d/nfs start   查看rpcinfo和export list rpcinfo –p showmount -e 192.168.159.120

 

 

7.          命令下设置diskless的引导环境

#The “pxeos” enables you to create a new operating system under /tftpboot and places the vmlinux and initrd images there. Options for “pxeos”: -a: Adds new O.S. -i: Description of O.S. -p: Protocol to use -D: If set to 1, then it indicates it’s diskless -s: NFS server -L: Location of your O.S., this should contain the vmlinuz and initrd somewhere in it. #生成NFS引导的内核文件 l  pxeos -a -i centoskernel -p NFS -D 1 -s 192.168.159.120 -L /diskless/centos/test4 centoskernel   #查看pxeos是否成功 l  pxeos -l   #查看NFS引导的内核文件是否生成 l  ll /tftpboot/linux-install/centoskernel/   #查看pxeos生成的配置文件 l  more /tftpboot/linux-install/pxelinux.cfg/pxeos.xml   The “pxeboot” command adds clients to the diskless environment and creates the HEX file for the host in the /tftpboot directory  Options for “pxeboot”: -a: Adds new host -O: Name of O.S. (You should have already created this with the system-config-netboot or pxeos) -r: Size of ram disk -S: Snapshot name of the diskless client. -e: The interface through which the pxe boot will take place. -N: NIS domain -s: Serial console settings to view remote consoles during boot up #生成diskless client所需要的启动文件，指定IP为192.168.159.130 l  pxeboot -a -O centoskernel -r 28753 -S test4 -e eth0 -s console=ttyS0,115200n8r 192.168.159.130   #也可以不用pxeboot命令，而用01+MAC地址作为文件名（注意小写,由于PXE的寻址规律） l  cat /tftpboot/linux-install/pxelinux.cfg/01-00-0c-29-a3-86-c3 default centoskernel label centoskernel     kernel centoskernel/vmlinuz     append console=ttyS0,9600n8 initrd=centoskernel/initrd.img root=/dev/ram0 init=disklessrc NFSROOT=192.168.159.120:/servers_drbd/centos/coreclient/test4 ramdisk_size=28753 ETHERNET=eth0 SNAPSHOT=test4

 

8.         新建一台Vmware,只需分配内存和CPU,作为diskless client

如何获取MAC地址:

diskless client启动时会广播DHCP request, 在Image Server中 tail -f /var/log/messages可以看到,根据step 7中的格式写入到/tftpboot/linux-install/pxelinux.cfg中,或者写入到step 3中的dhcpd.conf,并分配固定IP地址,然后用step 7中的pxeboot生成启动文件

l  tail -f /var/log/messages Dec 11 00:50:29 test3 dhcpd: DHCPDISCOVER from 00:0c:29:a3:86:c3 via eth0 Dec 11 00:50:29 test3 dhcpd: DHCPOFFER on 192.168.159.130 to 00:0c:29:a3:86:c3 via eth0 Dec 11 00:50:31 test3 dhcpd: DHCPREQUEST for 192.168.159.130 (192.168.159.120) from 00:0c:29:a3:86:c3 via eth0 Dec 11 00:50:31 test3 dhcpd: DHCPACK on 192.168.159.130 to 00:0c:29:a3:86:c3 via eth0   l  ls /tftpboot/linux-install/pxelinux.cfg/01-00-0c-29-a3-86-c3

 

9.          启动成功后可以检查diskless client和image server的同步情况

由于NFS设置成了sync模式,则在diskless client上的任何增删改操作都会实时同步到image server的nfs 挂载目录

 

 

 

参考资料：

http://www.linuxquestions.org/questions/red-hat-31/building-a-diskless-redhat-enterprise-linux-cluster-765393/

http://wiki.centos.org/zh/HowTos/DisklessClients