kvm

Mounting installation media for VM installation

This is acutally not a simple task in RH|CentOS.
  • CDROM mount passthrough from host to guest is not supported on my system at least…
  • Mounting an ISO image brings SELinux issues, qemu cannot access these directories initialls, additional configuration is necessary
  • I found the easiest approach is to access the install media via network protocols directly
  • In my first successful test I installed vsftpd and copied the CentOS DVD data to /var/ftp/pub/centos and accessed it via virtualization-manager
  • It is most probably a SELinux issue, found a solution for “Permission denied” when mounting .iso images
    • Had to use one command that allowed me to mount .iso e.g. located in /home/gans/KVM/install: setsebool -P virt_use_nfs 1
    • Maybe I also had to use virt-manager as root, but not sure about that

Important Files and directories

  • KVM Konfiguration Files: /etc/libvirt/qemu
  • Disk images: /var/lib/libvirt/images

Changes in the XML config files are implemented only after libvirtd service restart!

# systemctl restart libvirtd

Important commands

  • virt-manager
  • virt-install
  • virsh
  • virt-clone

virt-install

# virt-install --name test.example.com \
> --ram=1024 --vcpus=2 \
> --disk path=/var/lib/libvirt/images/test.example.com,size=16 \
> --graphics=spice \
> --location=ftp://192.168.122.100/pub/inst \
> --os-type=linux \
> --os-variant=rhel7

If a mistake happens during VM creation, Ctrl+C aborts the process, but the VM will be still running and the same name cannot be reused, because there is a configuration file and virtual disk. To get rid of this wrong VM….

virt-install with kickstart file

For Kickstart installations described later in this chapter, the virt-install command can be used to cite a Kickstart configuration file.

--extra-args="ks=ftp://192.168.122.1/pub/ks1.cfg"

Example:

# virt-install -n outsider1.example.org -r 1024 --disk \
path=/var/lib/libvirt/images/outsider1.example.org.img,size=16 \
-l ftp://192.168.122.1/pub/inst \
-x ks=ftp://192.168.122.1/pub/ks1.cfg

Working example from my lab with kickstart file. Important: It only worked with an ISO image as install source location !

virt-install --name server2.example.com --memory 1024 --vcpus 2 \
--disk /kvm/images/server2.example.com.img,size=16 \
--location /media/iso/CentOS-7-x86_64-Everything-1708.iso --os-type linux --os-variant rhel7 \
--network default --extra-args ks=http://192.168.122.1/inst/ks.cfg

Delete a VM from command line

  1. Stop the VM:

    # virsh destroy test.example.com

2. Delete associated XML configuration file in /etc/libvirt/qemu and virtual disk file in /var/lib/libvirt/images (not if it is to be reused)

# virsh undefine test.example.com --remove-all-storage
  1. Now virt-install can be run again with same name

virsh

VM management from the command line

  • Start VM
  • Stop VM
  • Delete VM
# virsh list --all
# virsh capabilities
# virsh start server1.example.com
# virsh shutdown server1.example.com
# virsh destroy server1.example.com
# virsh autostart server1.example.com
# virsh autostart --disable tester1.example.com

If you have to bring down a virbr interface on host like virbr0 bridge with ich also used by Oracle Virtualbox:

# sudo virsh net-destroy default

virt-clone

System to be cloned must be shutdown first

# virt-clone --original=server1.example.com \
> --name=tester1.example.com \
> --file=/var/lib/libvirt/images/tester1.example.com.img \
> --file=/var/lib/libvirt/images/tester1.example.com-1.img \
> --file=/var/lib/libvirt/images/tester1.example.com-2.img

IP addressing and also MAC address seems to be same like in the original image. To scale that kind of additional changes, the kickstart feature can be used.

Indices and tables