Xen的虚拟化分为半虚拟化以及全虚拟化技术，其中半虚拟化主要是通过修改 Linux 核心来完成的虚拟化技术。Xen 的半虚拟化技术主要是用在相同发行版本的 Linux 上，如果你想要使用半虚拟化的方式启动多个虚拟机器，那么虚拟机器全部都必须是相同的操作系统，甚至要求相同版本与相同核心的 Linux 发行版本。如果你想要安装不同版本的 Linux 或者是其他的 OS ( Windows XP) 时，那就得要使用全虚拟化技术了。
全虚拟化技术必须满足以下条件：
硬件支持 Intel 的 VT 技术 (Virtualization Technology, Intel-VT)；
硬件支持 AMD 的 SVM 技术 (Secure Virtual Machine, AMD-SVM or, AMD-V)。
下面来切实体验一下xen：
一、确定你的cpu是否支持虚拟化技术
# cat /proc/cpuinfo |grep flags |egrep -o 'pae|vmx|svm'
pae
svm
pae
svm
显示了PAE以及SVM，说明我的CPU支持全虚拟化技术。
二、安装Xen
1.安装Xen的基本程序
# yum install -y xen*
2.安装Xen的内核
# yum install -y kernel-xen*
3.安装Xen的虚拟管理程序
# yum install -y virt-manager
以上安装完毕，就来配置Xen的环境了。
三、配置Xen环境
修改grub.conf文件，以Xen的内核来启动系统
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You do not have a /boot partition. This means that
# all kernel and initrd paths are relative to /, eg.
# root (hd0,0)
# kernel /boot/vmlinuz-version ro root=/dev/sda1
# initrd /boot/initrd-version.img
#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/boot/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.18-238.12.1.el5xen)
root (hd0,0)
kernel /boot/xen.gz-2.6.18-238.12.1.el5
module /boot/vmlinuz-2.6.18-238.12.1.el5xen ro root=LABEL=/
module /boot/initrd-2.6.18-238.12.1.el5xen.img
title CentOS (2.6.18-238.el5)
root (hd0,0)
kernel /boot/vmlinuz-2.6.18-238.el5 ro root=LABEL=/
initrd /boot/initrd-2.6.18-238.el5.img
修改完毕，重启系统，shell界面就可以看到
# uname -a
Linux Xen 2.6.18-238.12.1.el5xen #1 SMP Tue May 31 14:02:29 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux
再看一下
# xm list
Name ID Mem(MiB) VCPUs State Time(s)
Domain-0 0 1228 2 r-----444.8
Xen的log所在地
# ll /var/log/xen/
total 44
drwx------ 2 root root 4096 May 10 05:30 console
-rw-r--r-- 1 root root 9653 Jun 10 15:07 domain-builder-ng.log
-rw-r--r-- 1 root root36 Jun 10 14:53 xend-debug.log
-rw-r--r-- 1 root root 17855 Jun 10 15:07 xend.log
-rw-r--r-- 1 root root36 Jun 10 15:07 xen-hotplug.log
四、建立虚拟机
准备工作
这里我们安装虚拟机采用NFS的方式，如果你对你的网络比较自信，也可以采用网络安装的方式，视具体情况而定。
创建一个NFS Server并将光盘根目录下的文件copy 进去，同时分享出来并允许Xen宿主机访问，这个不是重点，就不写过程了
下面进入真正的虚拟机安装阶段
# virt-install -n CentOS -r 512 --vcpus=1 \
> --nographic -f /opt/vm/centos.img -s 20 -p \
> -l nfs:192.168.1.249:/home/netinstall
解释一下各参数的意义：
-n 代表虚拟机的名字
-r 分配给虚拟机的内存
--vcpus 分配给虚拟机的CPU
--nographic 不适用图形界面
-f 虚拟机磁盘映像的所在地
-s 虚拟机磁盘映像的大小，单位记得是GB
-p 半虚拟化的方式
-l 安装映像的路径
PS：上面是采用NFS的方式，如果internet比较快，就换成internet上的源，门户网站sohu,163均有开源的镜像站点，另外中国科技大学的镜像站点也不错
# 开源镜像站点
163 http://mirrors.163.com
sohu http://mirrors.sohu.com
科大 http://mirrors.ustc.edu.cn
运行上面的安装虚拟机命令后，会提示以下的信息
Starting install...
Retrieving file vmlinuz... | 2.1 MB 00:00
Retrieving file initrd.img... 85% [=========================== ] 5.6 MB/s | 6.7 MB 00:00 ETA
Message from syslogd@ at Fri Jun 10 15:07:07 2011 ...
Xen kernel: Disabling IRQ #16
Retrieving file initrd.img... | 7.9 MB 00:00
Creating storage file... | 20 GB 00:00
Creating domain... |0 B 00:00
Connected to domain centos
Escape character is ^]
Bootdata ok (command line is method=nfs:192.168.1.249:/home/netinstall)
Linux version 2.6.18-238.el5xen (mockbuild@builder10.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)) #1 SMP Thu Jan 13 16:41:45 EST 2011
BIOS-provided physical RAM map:
Xen: 0000000000000000 - 0000000020800000 (usable)
No mptable found.
Built 1 zonelists. Total pages: 133120
Kernel command line: method=nfs:192.168.1.249:/home/netinstall
Initializing CPU#0
PID hash table entries: 4096 (order: 12, 32768 bytes)
Xen reported: 2812.790 MHz processor.
Console: colour dummy device 80x25
Dentry cache hash table entries: 131072 (order: 8, 1048576 bytes)
Inode-cache hash table entries: 65536 (order: 7, 524288 bytes)
Software IO TLB disabled
Memory: 496384k/532480k available (2529k kernel code, 27260k reserved, 1736k data, 196k init)
Calibrating delay using timer specific routine.. 7050.28 BogoMIPS (lpj=14100572)
Security Framework v1.0.0 initialized
SELinux: Initializing.
selinux_register_security: Registering secondary module capability
Capability LSM initialized as secondary
Mount-cache hash table entries: 256
CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line)
CPU: L2 Cache: 1024K (64 bytes/line)
CPU: Physical Processor ID: 0
CPU: Processor Core ID: 1
(SMP-)alternatives turned off
Brought up 1 CPUs
checking if image is initramfs... it is
Grant table initialized
NET: Registered protocol family 16
Brought up 1 CPUs
PCI: setting up Xen PCI frontend stub
ACPI: Interpreter disabled.
Linux Plug and Play Support v0.97 (c) Adam Belay
pnp: PnP ACPI: disabled
xen_mem: Initialising balloon driver.
usbcore: registered new driver usbfs
usbcore: registered new driver hub
PCI: System does not support PCI
PCI: System does not support PCI
NetLabel: Initializing
NetLabel: domain hash size = 128
NetLabel: protocols = UNLABELED CIPSOv4
NetLabel: unlabeled traffic allowed by default
NET: Registered protocol family 2
IP route cache hash table entries: 32768 (order: 6, 262144 bytes)
TCP established hash table entries: 131072 (order: 9, 2097152 bytes)
TCP bind hash table entries: 65536 (order: 8, 1048576 bytes)
TCP: Hash tables configured (established 131072 bind 65536)
TCP reno registered
audit: initializing netlink socket (disabled)
type=2000 audit(1307689628.858:1): initialized
VFS: Disk quotas dquot_6.5.1
Dquot-cache hash table entries: 512 (order 0, 4096 bytes)
Initializing Cryptographic API
alg: No test for crc32c (crc32c-generic)
ksign: Installing public key data
Loading keyring
- Added public key C099FB4D84A418B6
- User ID: CentOS (Kernel Module GPG key)
io scheduler noop registered
io scheduler anticipatory registered
io scheduler deadline registered
io scheduler cfq registered (default)
pci_hotplug: PCI Hot Plug PCI Core version: 0.5
rtc: IRQ 8 is not free.
Non-volatile memory driver v1.2
Linux agpgart interface v0.101 (c) Dave Jones
brd: module loaded
Xen virtual console successfully installed as xvc0
Bootdata ok (command line is method=nfs:192.168.1.249:/home/netinstall)
Linux version 2.6.18-238.el5xen (mockbuild@builder10.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)) #1 SMP Thu Jan 13 16:41:45 EST 2011
BIOS-provided physical RAM map:
Xen: 0000000000000000 - 0000000020800000 (usable)
No mptable found.
Built 1 zonelists. Total pages: 133120
Kernel command line: method=nfs:192.168.1.249:/home/netinstall
Initializing CPU#0
PID hash table entries: 4096 (order: 12, 32768 bytes)
Xen reported: 2812.790 MHz processor.
Console: colour dummy device 80x25
Dentry cache hash table entries: 131072 (order: 8, 1048576 bytes)
Inode-cache hash table entries: 65536 (order: 7, 524288 bytes)
Software IO TLB disabled
Memory: 496384k/532480k available (2529k kernel code, 27260k reserved, 1736k data, 196k init)
Calibrating delay using timer specific routine.. 7050.28 BogoMIPS (lpj=14100572)
Security Framework v1.0.0 initialized
SELinux: Initializing.
selinux_register_security: Registering secondary module capability
Capability LSM initialized as secondary
Mount-cache hash table entries: 256
CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line)
CPU: L2 Cache: 1024K (64 bytes/line)
CPU: Physical Processor ID: 0
CPU: Processor Core ID: 1
(SMP-)alternatives turned off
Brought up 1 CPUs
checking if image is initramfs... it is
Grant table initialized
NET: Registered protocol family 16
Brought up 1 CPUs
PCI: setting up Xen PCI frontend stub
ACPI: Interpreter disabled.
Linux Plug and Play Support v0.97 (c) Adam Belay
pnp: PnP ACPI: disabled
xen_mem: Initialising balloon driver.
usbcore: registered new driver usbfs
usbcore: registered new driver hub
PCI: System does not support PCI
PCI: System does not support PCI
NetLabel: Initializing
NetLabel: domain hash size = 128
NetLabel: protocols = UNLABELED CIPSOv4
NetLabel: unlabeled traffic allowed by default
NET: Registered protocol family 2
IP route cache hash table entries: 32768 (order: 6, 262144 bytes)
TCP established hash table entries: 131072 (order: 9, 2097152 bytes)
TCP bind hash table entries: 65536 (order: 8, 1048576 bytes)
TCP: Hash tables configured (established 131072 bind 65536)
TCP reno registered
audit: initializing netlink socket (disabled)
type=2000 audit(1307689628.858:1): initialized
VFS: Disk quotas dquot_6.5.1
Dquot-cache hash table entries: 512 (order 0, 4096 bytes)
Initializing Cryptographic API
alg: No test for crc32c (crc32c-generic)
ksign: Installing public key data
Loading keyring
- Added public key C099FB4D84A418B6
- User ID: CentOS (Kernel Module GPG key)
io scheduler noop registered
io scheduler anticipatory registered
io scheduler deadline registered
io scheduler cfq registered (default)
pci_hotplug: PCI Hot Plug PCI Core version: 0.5
rtc: IRQ 8 is not free.
Non-volatile memory driver v1.2
Linux agpgart interface v0.101 (c) Dave Jones
brd: module loaded
Xen virtual console successfully installed as xvc0
Event-channel device installed.
Uniform Multi-Platform E-IDE driver Revision: 7.00alpha2
ide: Assuming 50MHz system bus speed for PIO modes; override with idebus=xx
ide-floppy driver 0.99.newide
usbcore: registered new driver hiddev
usbcore: registered new driver usbhid
drivers/usb/input/hid-core.c: v2.6:USB HID core driver
PNP: No PS/2 controller found. Probing ports directly.
i8042.c: No controller found.
mice: PS/2 mouse device common for all mice
md: md driver 0.90.3 MAX_MD_DEVS=256, MD_SB_DISKS=27
md: bitmap version 4.39
TCP bic registered
Initializing IPsec netlink socket
NET: Registered protocol family 1
NET: Registered protocol family 17
XENBUS: Device with no driver: device/vbd/51712
XENBUS: Device with no driver: device/vif/0
Initalizing network drop monitor service
Write protecting the kernel read-only data: 498k
Greetings.
anaconda installer init version 11.1.2.224 starting
mounting /proc filesystem... done
creating /dev filesystem... done
mounting /dev/pts (unix98 pty) filesystem... done
mounting /sys filesystem... done
anaconda installer init version 11.1.2.224 using /dev/xvc0 as console
trying to remount root filesystem read write... done
mounting /tmp as ramfs... done
running install...
running /sbin/loader
其它的方法非常的简单，按提示来就行了。虚拟机完装好了，安装过程中可以通过ctrl+]回到宿主机。
五、虚拟机的一些管理命令
xm dm xen的dmesg信息
xm create CentOS 启动虚拟机centos
xm console centos 以文本方式连接至虚拟机
xm reboot centos 重启虚拟机
xm shutdown centos 关闭虚拟机
xm pause centos 暂停虚拟机
xm resume centos 恢复被暂停的虚拟机
………
虚拟机的配置文件位于/etc/xen下以虚拟机的名字为名称
name = "centos"
uuid = "5ec1488a-42ec-87a7-8001-49243f29497f"
maxmem = 512
memory = 512
vcpus = 1
bootloader = "/usr/bin/pygrub"
on_poweroff = "destroy"
on_reboot = "restart"
on_crash = "restart"
disk = [ "tap:aio:/opt/vm/centos.img,xvda,w" ]
vif = [ "mac=00:16:36:45:e1:b1,bridge=xenbr0,script=vif-bridge" ]
要想Xen虚拟机随开机自启动，要这样做
# ln -s /etc/xen/centos /etc/xen/auto/
# /etc/init.d/xendomains start
Starting auto Xen domains: centosUsing <class 'grub.GrubConf.GrubConfigFile'> to parse /grub/menu.lst
(skip)[done] [ OK ]