6 Managing A KVM Guest

Fedora 14 KVM Host:

KVM guests can be managed through virsh, the “virtual shell”. To connect to the virtual shell, run

virsh –connect qemu:///system

This is how the virtual shell looks:

[root@server1 ~]# virsh –connect qemu:///system
Welcome to virsh, the virtualization interactive terminal.
Type: ‘help’ for help with commands
‘quit’ to quit
virsh #

You can now type in commands on the virtual shell to manage your guests. Run


to get a list of available commands:

virsh # help
help print help
attach-device attach device from an XML file
attach-disk attach disk device
attach-interface attach network interface
autostart autostart a domain
capabilities capabilities
cd change the current directory
connect (re)connect to hypervisor
console connect to the guest console
cpu-baseline compute baseline CPU
cpu-compare compare host CPU with a CPU described by an XML file
create create a domain from an XML file
start start a (previously defined) inactive domain
destroy destroy a domain
detach-device detach device from an XML file
detach-disk detach disk device
detach-interface detach network interface
define define (but don’t start) a domain from an XML file
domid convert a domain name or UUID to domain id
domuuid convert a domain name or id to domain UUID
dominfo domain information
domjobinfo domain job information
domjobabort abort active domain job
domname convert a domain id or UUID to domain name
domstate domain state
domblkstat get device block stats for a domain
domifstat get network interface stats for a domain
dommemstat get memory statistics for a domain
domblkinfo domain block device size information
domxml-from-native Convert native config to domain XML
domxml-to-native Convert domain XML to native config
dumpxml domain information in XML
edit edit XML configuration for a domain
find-storage-pool-sources discover potential storage pool sources
find-storage-pool-sources-as find potential storage pool sources
freecell NUMA free memory
hostname print the hypervisor hostname
list list domains
migrate migrate domain to another host
migrate-setmaxdowntime set maximum tolerable downtime
net-autostart autostart a network
net-create create a network from an XML file
net-define define (but don’t start) a network from an XML file
net-destroy destroy a network
net-dumpxml network information in XML
net-edit edit XML configuration for a network
net-list list networks
net-name convert a network UUID to network name
net-start start a (previously defined) inactive network
net-undefine undefine an inactive network
net-uuid convert a network name to network UUID
iface-list list physical host interfaces
iface-name convert an interface MAC address to interface name
iface-mac convert an interface name to interface MAC address
iface-dumpxml interface information in XML
iface-define define (but don’t start) a physical host interface from an XML file
iface-undefine undefine a physical host interface (remove it from configuration)
iface-edit edit XML configuration for a physical host interface
iface-start start a physical host interface (enable it / “if-up”)
iface-destroy destroy a physical host interface (disable it / “if-down”)
managedsave managed save of a domain state
managedsave-remove Remove managed save of a domain
nodeinfo node information
nodedev-list enumerate devices on this host
nodedev-dumpxml node device details in XML
nodedev-dettach dettach node device from its device driver
nodedev-reattach reattach node device to its device driver
nodedev-reset reset node device
nodedev-create create a device defined by an XML file on the node
nodedev-destroy destroy a device on the node
nwfilter-define define or update a network filter from an XML file
nwfilter-undefine undefine a network filter
nwfilter-dumpxml network filter information in XML
nwfilter-list list network filters
nwfilter-edit edit XML configuration for a network filter
pool-autostart autostart a pool
pool-build build a pool
pool-create create a pool from an XML file
pool-create-as create a pool from a set of args
pool-define define (but don’t start) a pool from an XML file
pool-define-as define a pool from a set of args
pool-destroy destroy a pool
pool-delete delete a pool
pool-dumpxml pool information in XML
pool-edit edit XML configuration for a storage pool
pool-info storage pool information
pool-list list pools
pool-name convert a pool UUID to pool name
pool-refresh refresh a pool
pool-start start a (previously defined) inactive pool
pool-undefine undefine an inactive pool
pool-uuid convert a pool name to pool UUID
secret-define define or modify a secret from an XML file
secret-dumpxml secret attributes in XML
secret-set-value set a secret value
secret-get-value Output a secret value
secret-undefine undefine a secret
secret-list list secrets
pwd print the current directory
quit quit this interactive terminal
exit quit this interactive terminal
reboot reboot a domain
restore restore a domain from a saved state in a file
resume resume a domain
save save a domain state to a file
schedinfo show/set scheduler parameters
dump dump the core of a domain to a file for analysis
shutdown gracefully shutdown a domain
setmem change memory allocation
setmaxmem change maximum memory limit
setvcpus change number of virtual CPUs
suspend suspend a domain
ttyconsole tty console
undefine undefine an inactive domain
update-device update device from an XML file
uri print the hypervisor canonical URI
vol-create create a vol from an XML file
vol-create-from create a vol, using another volume as input
vol-create-as create a volume from a set of args
vol-clone clone a volume.
vol-delete delete a vol
vol-wipe wipe a vol
vol-dumpxml vol information in XML
vol-info storage vol information
vol-list list vols
vol-pool returns the storage pool for a given volume key or path
vol-path returns the volume path for a given volume name or key
vol-name returns the volume name for a given volume key or path
vol-key returns the volume key for a given volume name or path
vcpuinfo domain vcpu information
vcpupin control domain vcpu affinity
version show version
vncdisplay vnc display
snapshot-create Create a snapshot
snapshot-current Get the current snapshot
snapshot-delete Delete a domain snapshot
snapshot-dumpxml Dump XML for a domain snapshot
snapshot-list List snapshots for a domain
snapshot-revert Revert a domain to a snapshot
virsh #


shows all running guests;

list –all

shows all guests, running and inactive:

virsh # list –all
Id Name State
1 vm10 running
virsh #

If you modify a guest’s xml file (located in the /etc/libvirt/qemu/ directory), you must redefine the guest:

define /etc/libvirt/qemu/vm10.xml

Please note that whenever you modify the guest’s xml file in /etc/libvirt/qemu/, you must run the define command again!

To start a stopped guest, run:

start vm10

To stop a guest, run

shutdown vm10

To immediately stop it (i.e., pull the power plug), run

destroy vm10

Suspend a guest:

suspend vm10

Resume a guest:

resume vm10

These are the most important commands.



to leave the virtual shell.

7  Creating An LVM-Based Guest

Fedora 14 KVM Host:

LVM-based guests have some advantages over image-based guests. They are not as heavy on hard disk IO, and they are easier to back up (using LVM snapshots).

To use LVM-based guests, you need a volume group that has some free space that is not allocated to any logical volume. In this example, I use the volume group /dev/vg_server1 with a size of approx. 465GB…


[root@server1 ~]# vgdisplay
— Volume group —
VG Name vg_server1
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 3
VG Access read/write
VG Status resizable
Cur LV 2
Open LV 2
Max PV 0
Cur PV 1
Act PV 1
VG Size 465.56 GB
PE Size 4.00 MB
Total PE 119184
Alloc PE / Size 26420 / 103.20 GB
Free PE / Size 92764 / 362.36 GB
VG UUID aHRSbB-piY1-maoZ-OWPy-DHIy-Bl2F-MPD0y2
[root@server1 ~]#

… that contains the logical volume /dev/vg_server1/lv_root with a size of approx. 98GB and the logical volume /dev/vg_server1/lv_swap (about 5.5GB) – the rest is not allocated and can be used for KVM guests:


[root@server1 ~]# lvdisplay
— Logical volume —
LV Name /dev/vg_server1/lv_root
VG Name vg_server1
LV UUID QCl4x8-zR8r-yYZE-dNp1-leQk-ei9n-vTCcb4
LV Write Access read/write
LV Status available
# open 1
LV Size 97.66 GB
Current LE 25000
Segments 1
Allocation inherit
Read ahead sectors auto
– currently set to 256
Block device 253:0
— Logical volume —
LV Name /dev/vg_server1/lv_swap
VG Name vg_server1
LV UUID rRg2Ua-WBbi-8bjn-TC0E-DBf2-Gcr2-k1nivK
LV Write Access read/write
LV Status available
# open 1
LV Size 5.55 GB
Current LE 1420
Segments 1
Allocation inherit
Read ahead sectors auto
– currently set to 256
Block device 253:1
[root@server1 ~]#

I will now create the virtual machine vm11 as an LVM-based guest. I want vm11 to have 20GB of disk space, so I create the logical volume /dev/vg_server1/vm11 with a size of 20GB:

lvcreate -L20G -n vm11 vg_server1

Afterwards, we use the virt-install command again to create the guest:

virt-install –connect qemu:///system -n vm11 -r 512 –vcpus=2 –disk path=/dev/vg_server1/vm11 -c /vm/debian-500-amd64-netinst.iso –vnc –noautoconsole –os-type linux –os-variant debianlenny –accelerate –network=bridge:br0 –hvm

Please note that instead of -f ~/vm11.qcow2 I use –disk path=/dev/vg_server1/vm11, and I don’t need the -s switch to define the disk space anymore because the disk space is defined by the size of the logical volume vm11 (20GB).

Now follow chapter 5 to install that guest.

8 Links

– DONE –