Note! Backup your data first!

• Remove content in VM. Free some space, reduce filesystems, logical volumes etc. For example reduce home directory.

  # log in as root via serial, or via SSH.
  
  umount /home
  fsck /dev/mapper/VolGroup-lv_home
  lvresize --resizefs -L1G /dev/mapper/VolGroup-lv_home
  mount /home

• If you need to reduce the rootfs, boot from network, usb or cd/dvd. Then resize the filesystem. For example, edit guest to boot from systemrescuecd.

  lvresize -r -L8G /dev/VolGroup/lv_root

• Shrink physical volume. First move LV's to beginning.

  pvdisplay -m
  pvmove -v /dev/vda2:2296-2551 /dev/vda2:0-255 --alloc anywhere
  pvmove -v /dev/vda2:2552-2799 /dev/vda2:256-503 --alloc anywhere
  pvmove -v /dev/vda2:10428-12475 /dev/vda2:504-2551 --alloc anywhere
  pvresize -v --setphysicalvolumesize 16G /dev/vda2

• On the KVM host, reduce the LV.

  lvresize -L16G /dev/vg_kvm1/vmns2

• On the guest force fsck check at next boot, and reboot.

  touch /forcefsck
  reboot

• Add cdrom device.

  virsh edit vmns2
  <disk type='file' device='cdrom'>
    <driver name='qemu' type='raw'/>
    <source file='/isos/systemresucecd-x86-2.2.0.iso'/>
    <target dev='hdc' bus='ide'/>
    <readonly/>
    <address type='drive' controller='0' bus='1' unit='0'/>
  </disk>

• Boot from cdrom first.

  <os>
    <type arch='x86_64' machine='pc-0.12'>hvm</type>
    <boot dev='cdrom'/>
    <boot dev='hd'/>
  </os>

• Boot VM and reduce rootfs. When finished, remove the cdrom device and boot device.

• See: https://github.com/flegmatik/linux-rootfs-resize

  cd /opt
  rpm -ivh http://ftp-stud.hs-esslingen.de/pub/epel/6/i386/epel-release-6-8.noarch.rpm
  yum install git parted cloud-utils
  git clone https://github.com/flegmatik/linux-rootfs-resize.git
  cd linux-rootfs-resize
  ./install