Virtual disk images for the KVM-guests can be placed in /var/lib/libvirt by default. In case you prefer to use another location to store the disk images,SELinux will,by default,prevent access and the security context of that location needs to be changed in order to use it for KVM. To change the SELinux context when storing the images in another location (/vm for example):

[jensd @kvmhost ~ ] $ sudo semanage fcontext -a -t virt _image _t "/vm(/.*)?" [jensd @kvmhost ~ ] $ sudo restorecon -R /vm

Now,to add a new VM,we can use virt-install.

Example to add a windows-guest:

1 2 3 4 5 [jensd @kvmhost ~ ] $ sudo virt -install --connect qemu : / / /system -n vmwin7 -r 1024 --vcpus =2 --disk path = /var /lib /libvirt /images /vmwin7 .img ,size =10 --graphics vnc ,listen =0 .0 .0 .0 --noautoconsole --os - type windows --os -variant win7 --accelerate --network =bridge :virbr0 --hvm --cdrom /var /X17 -59186 .iso Starting install . . . Allocating 'vmwin7.img' | 10 GB 00 :00 :00 Creating domain . . . | 0 B 00 :00 :00 Domain installation still in progress . Waiting for installation to complete .

Explanation of the arguments that were given to virt-install:

• –connect qemu:///system : connect to KVM on the local system,we could also connect to another KVM-host and define our new VM there
• -n vmwin7 :name of the new VM: vmwin7
• -r 1024: amount of memory for the VM: 1GB
• –vcpus=2 : amount of virtual CPU’s for the VM: 2
• –disk path=/var/lib/libvirt/images/vmwin7.img,size=10 : where to store the virtual disk image of the VM and the size: 10GB
• –graphics vnc,listen=0.0.0.0 : how to display the VM’s console: via VNC accessible from outside
• –noautoconsole : do not automatically connect to the console
• –os-type windows –os-variant win7 : type of guest OS (from the list given above)
• –accelerate : use KVM HW-acceleration
• –network=bridge:virbr0 : network bridge to use
• –hvm : full virtualisation
• –cdrom /var/X17-59186.iso : location of the installation ISO

After launching the above command,you should be able to connect with VNC to the host and get on the console-display of the VM. The console displays what would normally,on a physical machine,appear on the attached monitor.

By default,VNC will use the first availablescreen on port 5900. To be sure which screen is used,we can use virsh to show the attached console-screens for VNC:

[jensd @kvmhost ~ ] $ sudo virsh vncdisplay vmwin7 :0

:0 means the first screen and real port 5900 as you can also see when checking with netstat which ports are currently listening:

[jensd @kvmhost ~ ] $ netstat -tln |grep :59 tcp 0 0 0 .0 .0 .0 :5900 0 .0 .0 .0 : * LISTEN

From this point,we can complete the windows installation as if it would be a normal physical system:

After completing the installation with VNC,we end up with a Windows-VM that is running on our KVM-host:

As for the networking part,we use the earlier created bridge (virbr0) to do NAT. This means that the KVM-host NAT’s all our connections to the real network connected to the KVM-host. If DHCP is active on that network,it can be used in the VM. Otherwise you will have to configure a static IP in the same subnet.

Example to add a Linux-guest:

To add a Linux guest,next to the already added Windows-guest is quite similar:

1 2 3 4 5 [jensd @kvmhost ~ ] $ sudo virt -install --connect qemu : / / /system -n vmdeb7 -r 512 --vcpus =1 --disk path = /var /lib /libvirt /images /vmdeb7 .img ,size =2 --graphics vnc ,listen =0 .0 .0 .0 --noautoconsole --os - type linux --os -variant debianwheezy --accelerate --network =bridge :virbr0 --hvm --cdrom /tmp /debian -7 .5 .0 -amd64 -netinst .iso Starting install . . . Allocating 'vmdeb7.img' | 2 .0 GB 00 :00 :00 Creating domain . . . | 0 B 00 :00 :02 Domain installation still in progress . You can reconnect to the console to complete the installation process .

As with the Windows-VM,after launching this command,you should be able to connect with VNC to the host and get on the console of the VM to complete theDebian installation.

To know which VNC-display number (and port) is used for a certain VM,the same command as used earlier should do:

[jensd @kvmhost ~ ] $ sudo virsh vncdisplay vmdeb7 :1

Above command gives :1 as result,meaning that the guest vmdeb7 can be contacted with VNC on port 5901:

After finishing the installation,weend up with a Linux guest running on top of our KVM-host. Which Linux distro we are using doesn’t matter since we’re doing full virtualization.

1 2 3 4 5 root @deb : ~ # uname -a Linux deb 3 .2 .0 -4 -amd64 #1 SMP Debian 3 .2 .60 -1 +deb7u3 x86 _64 GNU /Linux root @deb : ~ # cat /proc /cpuinfo |grep model model : 13 model name : QEMU Virtual CPU version 1 .5 .3

Considering network,the same as with the Windows VM applies here. Our connections are NATted trough the KVM-host and we can use the DHCP-server of our real network.

1 2 3 4 5 6 7 8 9 10 11 12 root @deb : ~ # ping -c1 8 .8 .8 .8 PING 8 .8 .8 .8 (8 .8 .8 .8 ) 56 (84 ) bytes of data . 64 bytes from 8 .8 .8 .8 : icmp _req =1 ttl =128 time =23 .8 ms -- - 8 .8 .8 .8 ping statistics -- - 1 packets transmitted , 1 received , 0 % packet loss , time 0ms rtt min /avg /max /mdev = 23 .855 /23 .855 /23 .855 /0 .000 ms root @deb : ~ # ip a show eth0 2 : eth0 : &lt ;BROADCAST ,LOWER _UP &gt ; mtu 1500 qdisc pfifo _fast state UP qlen 1000 link /ether 52 :54 :00 :33 :65 :75 brd ff :ff :ff :ff :ff :ff inet 192 .168 .202 .140 /24 brd 192 .168 .202 .255 scope global eth0 inet6 fe80 ::5054 :ff :fe33 :6575 /64 scope link valid_lft forever preferred _lft forever

More KVM actions

Besides creating VM’s,it’s a good thing to know some basic operations regarding VM-managent.

List the active virtual machines:

[jensd @kvmhost ~ ] $ sudo virsh --connect qemu : / / /system list Id Name State -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 7 vmwin7 running 8 vmdeb7 running

Get more information about a guest:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 [jensd @kvmhost ~ ] $ sudo virsh dominfo vmwin7 Id : 7 Name : vmwin7 UUID : f913c6fa -b597 -437d -b6f5 -797314e34847 OS Type : hvm State : running CPU (s ) : 2 CPU time : 20955 .1s Max memory : 1048576 KiB Used memory : 1048576 KiB Persistent : yes Autostart : disable Managed save : no Security model : selinux Security DOI : 0 Security label : system _u :system_r :svirt_t :s0 :c638 ,c926 (enforcing )

Stop a running guest:

To stop a running VM in a clean way (as you would press the power button to start the shutdown sequence):

[jensd @kvmhost ~ ] $ sudo virsh --connect qemu : / / /system shutdown vmdeb7 Domain vmdeb7 is being shutdown

This triggers a normal,clean,shutdown on the guest:

1 2 3 4 root @deb : ~ # Broadcast message from root @deb (Wed Aug 27 09 :09 :16 2014 ) : Power button pressed The system is going down for system halt NOW !

To force stop a running VM that doesn’t want to shutdown in a clean way:

[jensd @kvmhost ~ ] $ sudo virsh --connect qemu : / / /system destroy vmdeb7 Domain vmdeb7 destroyed

Start aguest:

[jensd @kvmhost ~ ] $ sudo virsh --connect qemu : / / /system start vmdeb7 Domain vmdeb7 started

Delete aguest:

First we need to make sure that the guest is stopped before it can be deleted. In case you don’t want the virtual disk image anymore either,you’ll have to delete it manually after undefining the guest.

[jensd @kvmhost ~ ] $ sudo virsh --connect qemu : / / /system destroy vmcen6 Domain vmcen6 destroyed [jensd @kvmhost ~ ] $ sudo virsh --connect qemu : / / /system undefine vmcen6 Domain vmcen6 has been undefined [jensd @kvmhost ~ ] $ sudo rm -f /var /lib /libvirt /images /vmcen6 .img

After removing a disk-image,it’s a good thing to refresh the storage pool of KVM:

[jensd @kvmhost ~ ] $ sudo virsh pool -refresh default Pool default refreshed

Automatically let a guest start when the host starts

When rebooting your host,you probably want some or all the guests that are defined on thathost to start at the same time. By default,the guest are not automatically started.

[jensd @kvmhost ~ ] $ sudo virsh --connect qemu : / / /system autostart vmdeb7 Domain vmdeb7 marked as autostarted [jensd @kvmhost ~ ] $ sudo virsh --connect qemu : / / /system dominfo vmdeb7 |grep Auto Autostart : enable

Part 3: Using KVM with the virt-manager GUI

Starting the GUI

Managing KVM with the CLI is not so difficult and it can be very handy to script certain day-to-day tasks. Sometimes,you just need to keep an overview and require a little more user-friendliness. For that,you can use virt-manager,which is a graphical interface for libvirt and is mainly built for KVM. When you want to manage your guest with virt-manager,you can either do it on the host itself,by starting an X-server locally or use X11 forwarding on a headless server (more informationhere).

Make sure that you have enough permissions to use virt-manager and simply execute virt-manager from the command line:

1 [root @kvmhost ~ ] # virt -manager

If all goes well,you should be presented with the virt-manager GUI:

Basic actions

From the initial start-up screen,you can immediately see a list of configured guests on this host and take actions on them like: Run,Pause,Shutdown,Reboot,Force off,…

When selecting a guest,you can also click on Open to display the console as we did earlier using VNC:

Advanced actions

Other possibilities using the virt-manager interface:

Connect to another host-system to manage the VM’s running there,using File -> Add connection (like using the –connect on the CLI)

Migrate a VM to another KVM-host: right click on the VM and choose Migrate…

Clone a VM to the same or another KVM-host: right click on the VM and choose Clone…

As you can see,the virt-manager interface is not very complicated and most of the basic tasks don’t need any explanation.

After completing all of the above steps,basic installation and using KVM shouldn’t have any secrets anymore for you. The next thing to do is experiment and test a little more with KVM and hopefully start to use it in your production environment.

url---http://jensd.be/207/linux/install-and-use-centos-7-as-kvm-virtualization-host

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