Libvirt cheatsheet

Remote connection over ssh

virt-manager -c qemu+ssh://root@10.0.0.1/system

In the installation/cloning examples below, I precreated LV using lvcreate. The path's given point to the LVs (For example /dev/xen02/member.root)
Installing without virtio might end up with a slow VM.

virt-install --name=member \
--ram 1024 \
--os-type linux --os-variant debianlenny \
--file /dev/xen02/member.root \
--network network=default \
--vnc \
--noautoconsole \
--hvm \
--cdrom /home/lmwangi/debian-505-amd64-netinst.iso
--force yes

Virtio speeds up things a lot.

virt-install --name=nms01 \
--ram 512 \
--os-type linux --os-variant debianlenny \
--disk path=/dev/dm-8,bus=virtio \
--network network=default,model=virtio \
--vnc \
--noautoconsole \
--cdrom /home/lmwangi/debian-505-amd64-netinst.iso
--virt-type kvm \
--force yes

Cloning is easy. Create/Install a template VM and clone it to create your workhorses.

virt-clone \
--prompt \
--connect qemu:///system \
--original template \
--name "champ" \
--file /dev/xen02/champ.root

By default, your default network should be started.

virsh net-start default && virsh net-autostart default

You can also view an existing VM's definition.

# virsh net-dumpxml default

default
900a487e-d5a6-b731-7bb0-3997fc0455fb







.....

You can also hotplug disks. The VM wasn't stable though :(

virsh # detach-disk
error: command 'detach-disk' requires option
error: command 'detach-disk' requires option
virsh # detach-disk nosql vdb
Disk detached successfully

virsh # attach-disk nosql /dev/xen02/nosql.storage vdb
Disk attached successfully

On the VM, you may need to

modprobe acpiphp

Occasionally, I have legacy VMs that were not properly created (Someone bypassed libvirt.) Cloning is a pain. In essence, I create a similar LV (same size), define a VM using the new LV and then dd over the LV

[root@vm01 ~]# lvdisplay cnix/box1_root
--- Logical volume ---
LV Name /dev/cnix/box1_root
VG Name cnix
LV UUID xxxx-xxxx.....
LV Write Access read/write
LV Status available
# open 1
LV Size 19.53 GB
Current LE 5000
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:12

[root@vm01 ~]# lvcreate -L 19.53G -n signer sdbvg
Rounding up size to full physical extent 19.53 GB
Logical volume "signer" created

[root@vm01 ~]# virt-clone --prompt --original legacy1 --name signer --file /dev/sdbvg/signer.root --file /dev/sdbvg/signer.swap
This will overwrite the existing path '/dev/sdbvg/signer.root'!
Do you really want to use this disk (yes or no) yes
This will overwrite the existing path '/dev/sdbvg/signer.swap'!

Do you really want to use this disk (yes or no) yes
Cloning /dev/cnix/legacy1_root | 20 GB 02:11
Cloning /dev/cnix/legacy1_swap | 2.0 GB 00:08

Clone 'signer' created successfully.

Sometimes this is not always flawless

virt-clone --prompt --original master --name master1 --file /dev/sdbvg/master1.root --file /dev/sdbvg/master1.swap
ERROR Domain 'master' was not found.
What is the name of the original virtual machine? master
ERROR Domain 'master' was not found.
What is the name of the original virtual machine? legacy1
ERROR Domain 'legacy1' was not found.
What is the name of the original virtual machine? ERROR

So we have to dd the image to the new hdd

[root@vm01 ~]# dd if=/dev/cnix/legacy1_root of=/dev/sdbvg/master1.root
dd if=/dev/cnix/legacy2_root of=/dev/sdbvg/member.root
40960000+0 records in
40960000+0 records out
20971520000 bytes (21 GB) copied, 1237.21 seconds, 17.0 MB/s

And boot the new VM