[libvirt] Instances

Dave Sayles sayles.dave at gmail.com
Sat Mar 28 19:03:32 UTC 2015


libvirt/qemu-kvm failing to start interfaces wasn't the problem (though I
thought it was since those interfaces weren't around when the VM wouldn't
start).  I eventually realized that the socket I was telling libvirt to
accept on was in the ephemeral port range, and a webserver I was running on
the same machine was accepting a bunch of connections at VM spin up time.

#mysterysolved

Thanks!

On 28 March 2015 at 14:29, Laine Stump <laine at laine.org> wrote:

> On 03/27/2015 12:42 PM, Dave Sayles wrote:
> > I'm running libvirt with qemu-kvm underneath.
> >
> > My network stack has the eth0 interface which is bridged to a br0
> interface.
> > Usually, when a VM starts up, a new "vnet" interface is created as well
> by
> > libvirt. That vnet interface has a matching HWaddr to the VM that was
> spun up
> > with it, so I'm assuming they're associated somehow.
>
> The vnetX device is a tap device created by libvirt for use by qemu. One
> end of the tap device is attached to the bridge, and the other end is a
> file descriptor which the qemu process connects to the guest's emulated
> network device.
>
> The MAC address of the tap device actually isn't identical to the MAC
> address used by the guest's emluated network device - the first byte is
> 0xFE, and all the other bytes match.
>
> >
> > Sometimes, after using libvirt's "virt-install" to create a VM, I'm
> unable to
> > "virsh start" it. Virsh will print this out to stderr that it couldn't
> start
> > that VM, since the connection was "Reset by peer".
> >
> > I've yet to find a repro case for this issue. Eventually, I am able to
> "virsh
> > start" the instance, but only after several minutes.
> >
> > Are there any known issues with libvirt/qemu-kvm failing to instantiate
> > network devices when it spins up VMs?
>
> What makes you think that is the problem?
>
> >
> > This is printed to the logs as well:
> >
> > Mar 27 16:21:07 localhost kernel: device vnet42 entered promiscuous mode
> > Mar 27 16:21:07 localhost kernel: br0: port 44(vnet42) entering
> forwarding
> > state
> > Mar 27 16:21:07 localhost logger: KVM: 43 guests now active
> > Mar 27 16:21:08 localhost kernel: br0: port 44(vnet42) entering disabled
> > state
> > Mar 27 16:21:08 localhost kernel: device vnet42 left promiscuous mode
> > Mar 27 16:21:08 localhost kernel: br0: port 44(vnet42) entering disabled
> > state
> > Mar 27 16:21:08 localhost logger: KVM: 42 guests now active
>
> None of those are error messages. They are all indications of normal
> operation.
>
> It you don't see any error messages attributes to libvirtd in the logs,
> try looking in /var/log/libvirt/$guestname.log
>



-- 
dgs3
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