basic virsh commands, extending partition in guest OS etc.

virsh_qemu.txt

# Basic command to manage VMs

# list all defined domains (VMs) and their status (running, shut off etc.)
virsh list --all

# stop VM (named _myvm_) gracefully
virsh shutdown _myvm_

# start VM
virsh start _myvm_

# enter VM, you can exit from VM by ^] (control and then ']')
virsh console _myvm_

# shutdown VM immediately, this is equivalent to pulling the plug off
virsh destroy _myvm_

# mark VM to be started automatically
virsh autostart _myvm_

# dump xml config (useful while cloning, renaming etc.)
virsh dumpxml _myvm_ > _myvm_.xml

# cloning

virt-clone -o  centos6template -n _newvm_ -f /srv/vmstore/_newvm__.img


#### how to extend VM filesystem,
# In below example we will be extending logical volume named lv_root (/dev/mapper/vg_root-lv_root)
# that is created on volume group named vg_root

# 1. stop VM, this is important
virsh shutdown _myvm_
# 2. resize qemu image, for example: add 2 gigabytes
cd /srv/vmstore/ && qemu-img  resize _myvm_ +2GB

# 3. start VM and configure LVM:

virsh start _myvm_
virsh console _myvm_

# now insinde guest OS:
fdisk /dev/vda  # add new partition that will be using added unused (yet) space

p
n
p (primary)
'partition number'
'First cylinder' number (see output from 'fdisk -l')
Last cylinder (+cylinders or +size{K,M,G}0
w
reboot VM guest
# assuming new partition is vda4, add it to lvm:
pvcreate /dev/vda4

# extend vg_root volume group
vgextend vg_root /dev/vda4

# extend logical volume to use 100% available space:
lvextend -l +100%FREE /dev/mapper/vg_root-lv_root

# resize ext4:
resize2fs  /dev/mapper/vg_root-lv_root

# done, no reboot necessary

# Extending _myvm_ memory to 4GB
# all commands to be issued on host OS

virsh  shutdown _myvm_

#command below will open text editor
# change <memory  .. > value to 4194304
# and also <currentMemory ..> value to 4194304 too
virsh edit _myvm_
virsh  setmaxmem _myvm_ 4194304
virsh  start _myvm_

# all done, _myvm_ now has 4GB of ram