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一、安装KVM
grep -E 'vmx|svm' /proc/cpuinfo #查看CPU是否支持KVM，只有支持才能做
lsmod | grep kvm #查看CPU是否支持KVM，只有支持才能做
yum install qemu-kvm qemu-kvm-tools virt-manager libvirt virt-install -y安装完毕通过下面命令都可以看到多出一个新的网络设备virbr0
brctl show
ifconfig设置libvirtd服务开机启动,libvirt对虚拟机不产生任何影响，只是用来管理的
systemctl enable libvirtd.service
systemctl start libvirtd.service
systemctl status libvirtd.serviceqemu-img工具创建磁盘
qemu-img create -f raw /opt/Centos-7.2-x86_64.raw 10G创建虚拟机
需要提前准备ISO镜像
virt-install --virt-type kvm --name Centos-7.2-x86_64 --ram 1024 --cdrom=/tmp/CentOS-7-x86_64-DVD-1511.iso --disk /opt/Centos-7.2-x86_64.raw --network network=default --graphics vnc,listen=0.0.0.0 --noautoconsole 紧接着用vncviewer工具，连接过去，然后安装虚拟机，注意关闭宿主机的防火墙和selinux
iptables -F
connect:宿主机:5900
选中Install CentOS7 ，按tab键，输入net.ifnames=0 biosdevname=0
分区那里不用设置swap分区。本身就是虚拟机了，再设置swap分区，效果很差.
最后一步要注意，点击reboot，它其实是关机。需要手动使用virsh命令启动
virsh常用命令
virsh --help
virsh list
virsh list --all
virsh shudown Centos-7.2-x86_64(主机名)
virsh destroy Centos-7.2-x86_64(主机名) 类似kill -9 进程号
virsh start Centos-7.2-x86_64
virsh undefine Centos-7.2-x86_64 #会删除/etc/libvirt/qemu的xml文件，可以通过dumpxml的xml恢复，前提是磁盘文件没有问题
virsh edit Centos-7.2-x86_64
virsh suspended Centos-7.2-x86_64
virsh resume Centos-7.2-x86_64
virsh dumpxml Centos-7.2-x86_64 > Centos-7.2-x86_64.backup
virsh define Centos-7.2-x86_64.backup
virsh autostart Centos-7.2-x86_64
ps -aux |grep kvm
KVM虚拟机配置文件说明
cat /etc/libvirt/qemu/Centos-7.2-x86_64.xml
vnc的端口是-1 表示监听再5900端口上
<graphics type='vnc' port='-1' autoport='yes' listen='0.0.0.0'>
这里是最大内存和当前内存，以及cpu数量
<memory unit='KiB'>4096000</memory>
<currentMemory unit='KiB'>1048576</currentMemory>
<vcpu placement='auto' current='1'>4</vcpu>
下面是硬盘路径和格式
<driver name='qemu' type='raw'/>
<source file='/opt/CentOS-7.1-x86_64.raw'/>
hvm表示硬件虚拟化
<type arch='x86_64' machine='pc-i440fx-rhel7.0.0'>hvm</type>
二、快照
快照配置文件在/var/lib/libvirt/qemu/snapshot/虚拟机名称/下
ls /var/lib/libvirt/qemu/snapshot/Centos-7.2-x86_64/快照命令
virsh --help | grep snapshot
snapshot-create Create a snapshot from XML
snapshot-create-as Create a snapshot from a set of args
snapshot-current Get or set the current snapshot
snapshot-delete Delete a domain snapshot
snapshot-dumpxml Dump XML for a domain snapshot
snapshot-edit edit XML for a snapshot
snapshot-info snapshot information
snapshot-list List snapshots for a domain
snapshot-parent Get the name of the parent of a snapshot
snapshot-revert Revert a domain to a snapshot转换磁盘的格式
raw磁盘格式的虚拟机不支持快照功能，要使用镜像功能，磁盘格式必须为qcow2
转换格式时虚拟机必须先关机
qemu-img convert -f raw -O qcow2 /opt/Centos-7.2-x86_64.raw /opt/Centos-7.2-x86_64.qcow2
qemu-img info /opt/Centos-7.2-x86_64.qcow2修改配置文件的disk模块，把磁盘改成最新的qcow2的这个文件，同时格式也改成qcow2的
virsh edit Centos-7.2-x86_64
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source file='/opt/Centos-7.2-x86_64.qcow2'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
</disk>改好之后，检查启动是否正常
virsh start Centos-7.2-x86_64
virsh shutdown Centos-7.2-x86_64快照备份，启动kvm和关闭的情况都可以快照
virsh snapshot-create Centos-7.2-x86_64 #每次创建一个快照之前，都可以在KVM虚拟机上touch一个文件，下面恢复快照的时候，可以检查该文件是否存在
virsh snapshot-list Centos-7.2-x86_64
virsh snapshot-create Centos-7.2-x86_64
virsh snapshot-list Centos-7.2-x86_64
virsh snapshot-current Centos-7.2-x86_64 # 查看当前快照
virsh snapshot-list Centos-7.2-x86_64
Name Creation Time State
------------------------------------------------------------
1533869463 2018-08-10 10:51:03 +0800 shutoff
1533869964 2018-08-10 10:59:24 +0800 running
1533869988 2018-08-10 10:59:48 +0800 running
1533870006 2018-08-10 11:00:06 +0800 running
virsh snapshot-revert Centos-7.2-x86_64 1533870006 #恢复到某个快照
virsh snapshot-revert Centos-7.2-x86_64 1533869964
virsh snapshot-delete Centos-7.2-x86_64 1533869502 #删除到某个快照
qemu-img info /opt/Centos-7.2-x86_64.qcow2 #qemu-img info也可以查看快照
image: /opt/Centos-7.2-x86_64.qcow2
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 2.2G
cluster_size: 65536
Snapshot list:
ID TAG VM SIZE DATE VM CLOCK
1 1533869463 0 2018-08-10 10:51:03 00:00:00.000
2 1533869964 380M 2018-08-10 10:59:24 00:05:47.239
3 1533869988 380M 2018-08-10 10:59:48 00:06:07.406
4 1533870006 380M 2018-08-10 11:00:06 00:06:21.841
Format specific information:
compat: 1.1
lazy refcounts: falseCPU和内存动态扩容
CPU和内存的动态扩容可以通过virt-install 命令实现
virt-install --help | grep cpu
--vcpus VCPUS Number of vcpus to configure for your guest. Ex:
--vcpus 5
--vcpus 5,maxcpus=10,cpuset=1-4,6,8
--vcpus sockets=2,cores=4,threads=2,
--cpu CPU CPU model and features. Ex:
--cpu coreduo,+x2apic
--cpu host-passthrough
--cpu host
virt-install --help | grep memory
usage: virt-install --name NAME --memory MB STORAGE INSTALL [options]
--memory MEMORY Configure guest memory allocation. Ex:
--memory 1024 (in MiB)
--memory 512,maxmemory=1024
--memory 512,maxmemory=1024,hotplugmemorymax=2048,hotplugmemoryslots=2
--memdev MEMDEV Configure a guest memory device. Ex:
--memtune MEMTUNE Tune memory policy for the domain process.
--memorybacking MEMORYBACKING
Set memory backing policy for the domain process. Ex:
--memorybacking hugepages=on
也通过修改配置文件实现,首先需要修改支持动态更改cpu和内存
<memory unit='KiB'>4096000</memory>
<currentMemory unit='KiB'>2097152</currentMemory>
<vcpu placement='auto' current='1'>4</vcpu>
动态修改cpu
virsh setvcpus Centos-7.2-x86_64 2 --liveKVM虚拟机查看 cat /proc/cpuinfo | grep processor | wc -l
另外动态修改CPU，只能动态的添加，不能动态的减少，如果要减少可以通过关闭kvm，修改配置文件操作
virsh dominfo Centos-7.2-x86_64 | grep CPU动态修改内存
virsh qemu-monistor-command Centos-7.2-x86_64 --hmp --cmd info balloon
virsh qemu-monitor-command Centos-7.2-x86_64 --hmp --cmd balloon 2048
virsh dominfo Centos-7.2-x86_64| grep memory另一种修改kvm内存的方式，另外修改内存不能超过最大内存
virsh setmem Centos-7.2-x86_64 748288在规划是考虑到想要热添加，当时装虚拟机的时候，就要考虑这个问题，设置max内存和cpu
关于硬盘扩容部分，虽然可以resize增大，但是有丢失数据的风险，生产中不推荐使用
KVM的网络部分
启动kvm虚拟机，会多出一个vnet0网络设备，这是虚拟启动后生成的。
ifconfig
virbr0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255
ether 52:54:00:2f:b1:73 txqueuelen 0 (Ethernet)
RX packets 13 bytes 1042 (1.0 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 5 bytes 670 (670.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
vnet0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500kvm虚拟机启动后，vnet0默认桥接到了virbr0上，关闭后消失
此时的kvm虚拟机出去的流量是接到virbr0上，然后经过宿主机的iptables的nat，再经过eth0出去
这就有网络瓶颈了，而且依靠iptables，如果你把iptables关闭无法上网了。同时ip地址是地址池中分配的内网地址
iptables -t nat -vnL
Chain POSTROUTING (policy ACCEPT 5 packets, 585 bytes)
pkts bytes target prot opt in out source destination
2 269 RETURN all -- * * 192.168.122.0/24 224.0.0.0/24
0 0 RETURN all -- * * 192.168.122.0/24 255.255.255.255
0 0 MASQUERADE tcp -- * * 192.168.122.0/24 !192.168.122.0/24 masq ports: 1024-65535
0 0 MASQUERADE udp -- * * 192.168.122.0/24 !192.168.122.0/24 masq ports: 1024-65535
0 0 MASQUERADE all -- * * 192.168.122.0/24 !192.168.122.0/24
7 855 POSTROUTING_direct all -- * * 0.0.0.0/0 0.0.0.0/0
7 855 POSTROUTING_ZONES_SOURCE all -- * * 0.0.0.0/0 0.0.0.0/0
7 855 POSTROUTING_ZONES all -- * * 0.0.0.0/0 0.0.0.0/0 #brctl show
bridge name bridge id STP enabled interfaces
virbr0 8000.5254002fb173 yes vnet0kvm获取的地址来源于下面
ps aux | grep dns #DNS服务
less /var/lib/libvirt/dnsmasq/default.conf #DNS配置文件