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