At work I always prefer KVM hosts for reasons such as flexible, free and GUI-less. Yet I never bothered to go deeper into the networking features of Libvirt, so I only connect VMs to the host networks via Linux Bridges or OvS. Far far away from fancy virtual libvirt networks.

Even with this simple networking approach I recently faced a tedious task of reconnecting VMs to different bridges on-the-fly.
My use case came from a need to connect a single traffic generator VM to the different access ports of virtual CPEs. Essentially this meant that I need to reconnect my traffic generator interfaces to different bridges back and forth:

scheme

Apparently there is no such virsh command that will allow you to change bridge attachments for networking devices, so a bit of bash-ing came just handy.

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virsh is a goto console utility for managing Qemu/KVM virtual machines. But when it comes to deletion of the VMs you better keep calm - there is no single command to destroy the VM, its definition XML file and disk image.

Probably not a big problem if you have a long-living VMs, but if you in a testing environment it is naturally to spawn and kill VMs quite often. Lets see how xargs can help us with that routine.

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Author's picture

Roman Dodin

Eagerness to learn & passion to share

Netdevops @ Nuage Networks

Russia