Virsh allows you to manage virtual machines from the command line. You can define new VMs by specifying their XML configuration files, list both active and inactive VMs, start and shutdown VMs, and edit VM attributes like CPUs, memory, and network interfaces by exporting the XML configuration, making changes, and reimporting it. USB devices can be passed through to VMs after modifying AppArmor settings and specifying the device's vendor and product IDs in the VM's XML configuration.

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Manage your virtual machines
From the shell
You can manage your VMs from the shell using virsh. You can get a list of the
available commands if you type "help". Type "help command" to get additional
infos for a particular command.
Define your new VM
Before you can manage your new VM with virsh, you must define it:
$ virsh --connect qemu:///system
Connecting to uri: qemu:///system
Welcome to virsh, the virtualization interactive terminal.
Type: 'help' for help with commands
'quit' to quit
virsh # define /etc/libvirt/qemu/newvm.xml
Domain newvm defined from /etc/libvirt/qemu/newvm.xml
Note that to list newvm, you must use 'list --inactive' or 'list --all', since
list without any options will only list currently running machines.
List your VMs
Virsh allows you to list the virtual machines available on the current host:
yhamon@paris:/etc/libvirt/qemu$ virsh --connect qemu:///system
Connecting to uri: qemu:///system
Welcome to virsh, the virtualization interactive terminal.
Type: 'help' for help with commands
'quit' to quit
virsh # help list
NAME
list - list domains
SYNOPSIS
list [--inactive | --all]
DESCRIPTION
Returns list of domains.
OPTIONS
--inactive list inactive domains
--all list inactive & active domains
virsh # list
Id Name State
----------------------------------
15 mirror running
16 vm2 running
virsh # list --all
Id Name State
----------------------------------
15 mirror running
16 vm2 running
- test5 shut off
Define, undefine, start, shutdown, destroy VMs
The VMs you see with list --all are VMs that have been "defined" from an XML
file. Every VM is configured via a XML file in /etc/libvirt/qemu. If you want to
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remove a VM from the list of VMs, you need to undefine it:
virsh # undefine test5 # WARNING: undefine will delete your XML file!
Domain test5 has been undefined
virsh # list --all
Id Name State
----------------------------------
15 mirror running
16 vm2 running
To be able to undefine a virtual machine, it needs to be shutdown first:
virsh # shutdown mirror
Domain mirror is being shutdown
This command asks for a nice shutdown (like running shutdown in command line).
Notice: Ubuntu 10.04 server doesn't have acpid installed by default. This
package needs to be installed on the guest OS before it will listen to any
requests from the host.
You can also use "destroy", the more brutal way of shutting down a VM,
equivalent of taking the power cable off:
virsh # destroy mirror
Domain mirror destroyed
If you have made a change to the XML configuration file, you need to tell KVM to
reload it before restarting the VM:
virsh # define /etc/libvirt/qemu/mirror.xml
Domain mirror defined from /etc/libvirt/qemu/mirror.xml
Then, to restart the VM:
virsh # start mirror
Domain mirror started
Suspend and resume a Virtual Machine
Virsh allows you to easily suspend and resume a virtual machine.
virsh # suspend mirror
Domain mirror suspended
virsh # resume mirror
Domain mirror resumed
Editing the attributes of a Virtual Machine
libvirt stores it's configuration as xml in '/etc/libvirt/qemu'. The xml is easy
to understand, and is similar to VMware *.vmx files. While it is possible to
edit these files in place and restart libvirt-bin for the changes to take
affect, the recommended method for modifying the attributes of a virtual machine
is via virsh (or virt-manager, if it supports changing the hardware you want to
change). The concept is simple:
export (aka 'dump') the xml of the virtual machine you want to edit
edit the xml
import (aka 'define') the xml
For example, to edit the machine named 'foo' (you can get a list of your
machines with 'virsh list --all'), do:
$ virsh dumpxml foo > /tmp/foo.xml
(edit /tmp/foo.xml as needed)
$ virsh define /tmp/foo.xml
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Adding CPUs
KVM allows you to create SMP guests. To allocate two CPUs to a VM, dump the xml
as above, then edit your xml to have:
<domain type='kvm'>
...
<vcpu>2</vcpu>
...
</domain>
Now define the VM as above.
Adding Memory
To change the memory allocation in a VM, dump the xml as above, then edit your
xml to have:
<domain type='kvm'>
...
<memory>262144</memory>
<currentMemory>262144</currentMemory>
...
</domain>
Now define the VM as above. Keep in mind that the memory allocation is in
kilobytes, so to allocate 512MB of memory, use 512 * 1024, or 524288.
Changing the Network Card Model
kvm and qemu currently default to using the rtl8139 NIC. Supported NICs in
Ubuntu 8.04 LTS are i82551, i82557b, i82559er, ne2k_pci, pcnet, rtl8139, e1000,
and virtio. To use an alternate NIC, dump the xml as above, then edit your xml
to have:
<domain type='kvm'>
...
<interface type='network'>
...
<model type='e1000'/>
</interface>
...
</domain>
Now define the VM as above.
Adding USB Device Pass-through
Limitations
USB protocol 1.1 only
Device must be plugged in before KVM starts
Apparmor modifications needed
Apparmor Modification
In order for a software program to access the usb device correctly the apparmor
must be changed. Edit /etc/apparmor.d/abstractions/libvirt-qemu and uncomment
some lines.:
# WARNING: uncommenting these gives the guest direct access to host hardware.
# This is required for USB pass through but is a security risk. You have been
# warned.
/sys/bus/usb/devices/ r,
/sys/devices/*/*/usb[0-9]*/** r,
/dev/bus/usb/*/[0-9]* rw,
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After making the changes apparmor must be restarted.:
$ sudo /etc/init.d/apparmor restart
Adding USB devices
First find the usb Vendor ID and Product ID.:
$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 005 Device 012: ID 0a5c:2110 Broadcom Corp. Bluetooth Controller
Bus 005 Device 003: ID 0483:2016 SGS Thomson Microelectronics Fingerprint Reader
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
In the event that the Broadcom Corp. Bluetooth Controller wans to be selected
the vendor and product ids are 0a5c and 2110 respectively. These can be entered
into the xml profile. This can be done through virsh through the edit <domain>
command.:
<domain type='kvm'>
<name>windowsxp</name>
…
<devices>
…
<hostdev mode='subsystem' type='usb'>
<source>
<vendor id='0x0a5c'/>
<product id='0x2110'/>
</source>
</hostdev>
</devices>
</domain>
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