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How to live migrate with copy-storage-inc and zfs snapshot replication?
by Dan Vatca 22 May '24

22 May '24

Hello everybody, I am trying to understand how I can create a setup with two libvirt + kvm + zfs systems, in which I can: 1. Create a domain on sys-a, with storage space on a zfs filesystem. This filesystem stores the qcow2 image, any qcow2 disk snapshots, memory dumps and domain XML definition. 2. Take consistent ZFS snapshots every 15 minutes, and sync them to sys-b. The snapshots will be replicated using syncoid. These will be using scripts to quiesce the VM. 3. Given that most of the disk is synced (at most 15 minutes ago), what are the things I need to ensure (libvirt snapshots, memory snapshot, etc), so that I can do a live migration while copying just the incremental changes since the last snapshot I already transferred? I was trying to use virsh migrate —copy-storage-inc, however I could not find any working example that would copy just the incremental changes. I could find the theory of the snapshot backing chain, however —copy-storage-inc complains that it cannot replicate while there are snapshots present. (error: Requested operation is not valid: cannot migrate domain with 1 snapshots). I this scenario possible? Dan Vatca

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Guests: Unable to get IP address
by Arun Mani J 21 May '24

21 May '24

Hey all. I'm exploring virt-manager, libvirt etc. I downloaded Debian 12 KDE ISO and when launched using virt-manager, it does not seem to connect to network. nmcli says it has failed to get an IP address. However, if I run the same ISO inside GNOME Boxes, then it is able to connect to network. I checked the XML configuration of both and found this: ```xml <interface type="user"> <mac address="52:54:00:ea:f9:69"/> <model type="virtio"/> <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/> </interface> ``` However, the one created via virt-manager has this: ```xml <interface type="network"> <mac address="52:54:00:5d:c7:9e"/> <source network="default"/> <model type="virtio"/> <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/> </interface> ``` What I'm not able to understand is, why does the user mode networking work fine but not network mode? My ultimate goal is to set up routed configuration, so one can directly SSH into the guests. Packages: - virt-manager - 4.1.0 (Debian) - libvirt0 - 10.3.0-3 (Debian) - GNOME Boxes - 46.0 (Flatpak) Please let me know if you need any other information. It is a pretty much clean installation with no extra configuration, so I don't think I messed up anything. Thank you! Arun Mani J

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stats : active memory / disk latency
by Peter Quiring 21 May '24

21 May '24

Two stats that VMWare offers that I can't seem to find in libvirt is "active" memory and disk latency. Any idea how I could extract these stats? libvirt offers memory stats such as maximum, current, unused, usable, etc. but these are all 100% or 0% of what the VM has available. Looking for an "active" value. /proc/memstat has similar stats within a Linux VM but need to get from libvirt. Disk latency is also sometimes critical information. Thanks, -- Peter Quiring

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qemu guest agent with openbsd
by Christian Haumesser 13 May '24

13 May '24

Hello, I have an OpenBSD 7.5 guest running on Debian bookworm with libvirt (9.0) and qemu (7.2). I'd like to use the qemu guest agent in this guest, but I can't seem to figure out how to craft the libvirt xml to expose the serial port in a way that OpenBSD and libvirt can use it together (or if it’s even possible). Per the libvirt docs <https://wiki.libvirt.org/Qemu_guest_agent.html>, I’m currently using: > <channel type='unix'> > <source mode='bind'/> > <target type='virtio' name='org.qemu.guest_agent.0'/> > </channel> But OpenBSD doesn’t directly support the virtio console driver. Consistent with this 2020 thread <https://undeadly.org/cgi?action=article;sid=20200514073852> from the OpenBSD ports making list, I see the following message in my guest’s dmesg output: > virtio5 at pci0 dev 10 function 0 "Qumranet Virtio Console" rev 0x00 > virtio5: no matching child driver; not configured Thanks to this libvir-list thread <https://listman.redhat.com/archives/libvir-list/2015-October/120250.html> from 2015, I’ve realized that I can manually expose an ISA serial console that will allow me to connect to the guest agent using native qemu tooling; but there doesn’t seem to be a way to create a channel that libvirt can communicate over without virtio console support in the guest. The thread discusses a couple of approaches to resolving this issue with code changes, but it seems like the discussion stalled out before anything happened. Am I missing something or is it still impossible? Thanks!

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jfKVM - new app using libvirt
by Peter Quiring 07 May '24

07 May '24

jfKVM is a new web-based VM management system based on libvirt. jfkvm.sf.net https://pquiring.github.io/javaforce/projects/jfkvm/docs/help.html Thanks, -- Peter Quiring

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What's wrong with internal VM snapshots?
by Marius Vollmer 06 May '24

06 May '24

Hi! I am trying to improve the support for VM snapshots in the Cockpit web console, and I am afraid I have questions... We have been asked to prefer the "external" over the "internal" snapshot format, at least on RHEL. I haven't yet figured out why, and consequently I am struggling with deciding how hard the Cockpit UI should push people towards external snapshots. So, what's wrong with internal snapshots? I heard they are "unreliable", but how so in detail? Does the data structure inside the qcow2 files get corrupted easily? Do they behave poorly when the snapshot process runs out of disk in the middle? That sort of thing would help me a lot to figure out what Cockpit should be doing on platforms other than RHEL. And how well (or how soon) can external snapshots be expected to work? I have severely messed up my libvirt state a couple of times while playing around with them, and my confidence in them right now isn't great. :-) Are you surprised by this? Or are external snapshots not yet considered ready? (Most recent example from my experiments: Deleting a full system snapshot of a paused machine fails with "internal error: unable to execute QEMU command 'block-commit': Block node is read-only". Reverting to it works and after that it can also be deleted, all while the VM is paused.) Thanks!

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Error Cannot acquire state change lock from remoteDispatchDomainMigratePrepare3Params during live migration of domains
by Christian Rohmann 25 Apr '24

25 Apr '24

Hallo libvirt-users! we observe lock-ups / timeouts with in prometheus-libvirt-exporter (https://github.com/inovex/prometheus-libvirt-exporter) when libvirt is live-migrating domains: > Timed out during operation: cannot acquire state change lock (held by > monitor=remoteDispatchDomainMigratePrepare3Params) All of the source code can be found at: https://github.com/inovex/prometheus-libvirt-exporter/blob/master/pkg/expor…. Basically the error happens when DomainMemoryStats or other operational domain info is queried via the libvirt socket. 1) We are actually using the read-only socket at '/var/run/libvirt/libvirt-sock-ro', so there should not be any locking required. Is there any way to not run into lock contention, like running a request with some "nolock" indication? 2) This being reported as timeout waiting for the lock, what is the timeout and would waiting a bit longer help? Or is the lock active during the whole time a domain live migration is running? 3) Is this in any way related to the type of migration? Tunneled vs. native (https://libvirt.org/migration.html)? 4) Is there any indication that we could use to skip those domains (or certain queries)? The same issue was actually previously reported for another implementation of a Prometheus exporter (https://github.com/kumina/libvirt_exporter/issues/33) Currently the exporter locks up or throws the mentioned timeout errors during the the migration of 200 domains, 5 at a time. It would be awesome to find a way to make this work as smooth as possible, even during live migrations! I am thankful for any insights into how the libvirt socket, the various calls, the locking mechanisms or live migration modes work! Regards Christian

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How to configure the default connection for virsh
by Nir Soffer 19 Apr '24

19 Apr '24

We are using minikube vms, which require adding the user to to libvirt group[1]. We use `virsh -c qemu:///system` for debugging these vms or related libvirt networks. Using virsh without specifying the '-c' argument is a common mistake that leads to trouble, for example creating the libvirt default network incorrectly. I wonder if it is possible to configure virsh so it uses -c qemu:///system by default? We know that this is not great, but we don't know a better way to use minikube with the kvm2 driver. The minikube vms are started for creating a development environment and during CI, and they cannot require a password or any complicated setup. [1] https://github.com/kubernetes/minikube/issues/3467 Nir

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Linking virtual sound cards in two virtual machines?
by Lars Kellogg-Stedman 16 Apr '24

16 Apr '24

I would like to create a virtual audio cable between two libvirt guests such that sound output from guest A goes to sound input on guest B, and vice versa. I figure the solution to this is using something like the pulseaudio's "virtual sink", but I'm not entirely sure what the syntax would look like (fwiw, I'm on Fedora 39, which means libvirt 9.7.0, which means this has to be through libvirt's pulseaudio driver rather than the pipewire driver, since the latter isn't available in 9.7.0). I started by creating a virtual sink (and yes, I realize that's only half the process): pactl load-module module-null-sink sink_name=vaudio0 And adding the following snippet to the domain xml for guest "node1.virt": <audio id='1' type='pulseaudio'> <input name='vaudio0' streamName='node1-in' latency='100'/> <output name='vaudio0' streamName='node1-out' latency='100'/> </audio> But trying to start this guest results in: error: Failed to start domain 'node1.virt' error: internal error: process exited while connecting to monitor: audio: Could not init `pa' audio driver There doesn't appear to be any additional information in /var/log/libvirt/qemu/node1.virt.log. I'm wondering if someone has an example of what this might look like? Thanks, -- Lars Kellogg-Stedman <lars(a)redhat.com>

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'nconnect' nfs mount option support
by Abhisar Sinha 15 Apr '24

15 Apr '24

Hi, Is there a way to specify the 'nconnect' nfs mount opt value in the XML file used by 'virsh create-pool' command? If not, how hard would it be to implement this functionality? Please advise. Thanks, Abhisar

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