September 2025 - Users - libvirt List Archives

[libvirt-users] bridge / ubuntu / no arp reply
by François Chenais 15 Oct '26

15 Oct '26

Hello I'm trying to setup a bridged guest on an ubuntu 13.10 but it doesn't work. (Everything is ok with NAT) Network sniffing shows that arp replies don't come back to the guest. Test 1 ------ Guest : ping host_bridge_ip (ok) Test 2 ------ Guest: ping other_lan_host (KO) other_lan_host - receives arp who-is request - sends arp reply - arp -a shows the guest macaddr => Guest doesn't receive reply Test 3 ------ other_lan_host ping the Guest (KO) - arp -a shows "incomplete" addr - Guest receives nothing On Host ------- network tcpdump on bridge or vnet interfaces shows request but no reply ... Thanks in advance for help or ideas François

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Co-stop with non-VMware virtualization?
by Troels Arvin 04 Nov '25

04 Nov '25

Hello, How important is it to consider "co-stop" with non-VMWare virtualization such as KVM? I haven't been able to find anything about this for KVM, but there's some material about it for VMWare (albeit typically rather old material). Based on VMWare material, by "co-stop" I mean the following situation: A VM called "x" has been assigned quite a few vCPUs, e.g. 10, on a hypervisor with e.g. 20 physical cores. The hypervisor is hosting many other VMs, and the many VMs take turn running on the hardware. Now, if it's often the case that, e.g., only 7 physical threads are available when it's x's turn to run, the hypervisor needs to postpone running x till all 10 cores can be allocated at the same time. During this waiting time, x is stopped (co-stop). Is my understanding correct? Or will KVM allow x to run on (e.g.) 7 cores, even though the VM thinks it has 10 vCPUs available? It's my understanding that with KVM, the co-stopped situation is reflected in the VM's "steal time" metric in a tool like "top". Does hyperthreading in either the hypervisor and/or the guest impact the risk of co-stop? -- Regards, Troels Arvin

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Re: domain not getting IP address
by Pavel Mores 22 Sep '25

22 Sep '25

On Thu, Sep 18, 2025 at 11:29 AM Pavel Mores <pmores(a)redhat.com> wrote: > On Thu, Sep 18, 2025 at 10:25 AM Martin Kletzander <mkletzan(a)redhat.com> > wrote: > >> On Wed, Sep 17, 2025 at 04:02:12PM +0200, Pavel Mores wrote: >> >On Wed, Sep 17, 2025 at 3:05 PM Martin Kletzander <mkletzan(a)redhat.com> >> >wrote: >> > >> >> On Wed, Sep 17, 2025 at 02:14:51PM +0200, Pavel Mores via Users wrote: >> >> >Hi, >> >> > >> >> >I'm examining a domain that's connected to the 'default' network >> >> > >> >> ># virsh net-dumpxml default >> >> ><network connections='1'> >> >> > <name>default</name> >> >> > <uuid>c757baa7-2b31-4794-9dfb-0df384575602</uuid> >> >> > <forward mode='nat'> >> >> > <nat> >> >> > <port start='1024' end='65535'/> >> >> > </nat> >> >> > </forward> >> >> > <bridge name='virbr0' stp='on' delay='0'/> >> >> > <mac address='52:54:00:37:b7:92'/> >> >> > <ip address='192.168.122.1' netmask='255.255.255.0'> >> >> > <dhcp> >> >> > <range start='192.168.122.2' end='192.168.122.254'/> >> >> > </dhcp> >> >> > </ip> >> >> ></network> >> >> > >> >> >> >> This is standard. >> >> >> >> >using a device as follows: >> >> > >> >> ><interface type='network'> >> >> > <mac address='52:54:00:ed:06:2e'/> >> >> > <source network='default' >> portid='83db8ca9-baed-47f3-ba0d-1a967ee86aa5' >> >> >bridge='virbr0'/> >> >> > <target dev='vnet19'/> >> >> > <model type='virtio'/> >> >> > <alias name='net0'/> >> >> > <address type='pci' domain='0x0000' bus='0x00' slot='0x02' >> >> >function='0x0'/> >> >> ></interface> >> >> > >> >> >> >> This looks fine. >> >> >> >> >The domain is running but apparently without an IP address: >> >> > >> >> ># virsh domifaddr podvm-podsandbox-totok-8f10756a >> >> > Name MAC address Protocol Address >> >> >> >> >> >------------------------------------------------------------------------------- >> >> > >> >> >> >> This shows that libvirt does not know about any IP address. Does >> adding >> >> "--source agent", "--source arp" or "--source lease" change anything? >> >> >> > >> >'arp' and 'lease' don't but >> > >> ># virsh domifaddr --source agent podvm-podsandbox-totok-8f10756a >> >error: Failed to query for interfaces addresses >> >error: argument unsupported: QEMU guest agent is not configured >> > >> >This is surprising to me since this is a peer pods setup where the domain >> >in question is a podvm running an image which I was told does have >> >the qemu agent running. >> > >> >However the agent shouldn't be necessary for IP address acquisition I >> guess, >> >right? >> > >> >>The requisite host-side interfaces look good (to me anyway :-)): >> >> > >> >> >10: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc htb >> state UP >> >> >group default qlen 1000 >> >> > link/ether 52:54:00:37:b7:92 brd ff:ff:ff:ff:ff:ff >> >> > inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0 >> >> > valid_lft forever preferred_lft forever >> >> >[...] >> >> >35: vnet19: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue >> >> master >> >> >virbr0 state UNKNOWN group default qlen 1000 >> >> > link/ether fe:54:00:ed:06:2e brd ff:ff:ff:ff:ff:ff >> >> > inet6 fe80::fc54:ff:feed:62e/64 scope link proto kernel_ll >> >> > valid_lft forever preferred_lft forever >> >> > >> >> >I can share more information about the setup if necessary but I'll >> stop >> >> >here for now since I feel this must be just a simple stupid oversight >> on >> >> my >> >> >part. Please let me know if you'd like to have additional info. >> >> > >> >> >> >> When this happens to me sometimes, it's most often a firewall issue and >> >> the VM does not get any IP address or cannot communicate outside its >> >> network. >> >> >> > >> >I've seen a firewall suggested as a possible culprit, yes, however I >> don't >> >quite >> >know what it should look like. iptables appear unconfigured: >> > >> ># iptables -L -v -n >> >Chain INPUT (policy ACCEPT 0 packets, 0 bytes) >> > pkts bytes target prot opt in out source >> >destination >> > >> >Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) >> > pkts bytes target prot opt in out source >> >destination >> > >> >Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes) >> > pkts bytes target prot opt in out source >> >destination >> > >> >`nft list ruleset` lists only rules that look managed by libvirt >> >itself(*). At any >> >rate the host machine has no specific hand-configured firewall that I >> know >> >of. >> > >> > >> >> What it can be here is that there are some access issues to the dnsmasq >> >> lease file. >> >> >> >> What's in your /var/lib/libvirt/dnsmasq/virbr0.status file on the host? >> >> >> > >> >It's empty. >> > >> >Thanks Martin! >> >pvl >> > >> >(*) # nft list ruleset >> >table ip libvirt_network { >> >chain forward { >> >type filter hook forward priority filter; policy accept; >> >counter packets 85854914 bytes 398726525237 jump guest_cross >> >counter packets 85854914 bytes 398726525237 jump guest_input >> >counter packets 34777368 bytes 3386943972 jump guest_output >> >} >> > >> >chain guest_output { >> >ip saddr 192.168.122.0/24 iif "virbr0" counter packets 0 bytes 0 accept >> >> This suggests there were no incoming packets from an IP address in the >> range on the bridge. >> >> >iif "virbr0" counter packets 0 bytes 0 reject >> >> And no packets from outside of that range that would fall through to >> this above rule. >> >> [...] >> >> >} >> > >> >chain guest_input { >> >> [...] >> >> >oif "virbr0" ip daddr 192.168.122.0/24 ct state established,related >> counter >> >packets 0 bytes 0 accept >> >> No packets sent to the address range on the bridge, but >> >> >oif "virbr0" counter packets 0 bytes 0 reject >> >> basically no packets sent at all. >> >> >} >> > >> >chain guest_cross { >> >iif "openshift-412" oif "openshift-412" counter packets 0 bytes 0 accept >> >iif "openshift-419" oif "openshift-419" counter packets 0 bytes 0 accept >> >iif "openshift-416" oif "openshift-416" counter packets 0 bytes 0 accept >> >iif "openshift-415" oif "openshift-415" counter packets 0 bytes 0 accept >> >iif "openshift-413" oif "openshift-413" counter packets 0 bytes 0 accept >> >iif "virbr0" oif "virbr0" counter packets 0 bytes 0 accept >> >> No intra-network communication >> >> [...] >> >> >chain guest_nat { >> >type nat hook postrouting priority srcnat; policy accept; >> >> [...] >> >> >ip saddr 192.168.122.0/24 ip daddr 224.0.0.0/24 counter packets 50 bytes >> >3676 return >> >> There were some IPv4 multicast packets, but these could've originated >> from the host. >> >> >ip saddr 192.168.122.0/24 ip daddr 255.255.255.255 counter packets 0 >> bytes >> >0 return >> >> And no broadcast packets from the address space. >> >> >meta l4proto tcp ip saddr 192.168.122.0/24 ip daddr != 192.168.122.0/24 >> >counter packets 0 bytes 0 masquerade to :1024-65535 >> >meta l4proto udp ip saddr 192.168.122.0/24 ip daddr != 192.168.122.0/24 >> >counter packets 0 bytes 0 masquerade to :1024-65535 >> >ip saddr 192.168.122.0/24 ip daddr != 192.168.122.0/24 counter packets 0 >> >bytes 0 masquerade >> >> No NAT, anything. >> >> [...] >> >ip saddr 192.168.14.0/24 ip daddr 224.0.0.0/24 counter packets 50 bytes >> >3675 return >> >> These counters on another range are the same, so I would say all the >> multicast packets on the range we are interested in are just the same, >> hence having nothing to do with the guest. >> >> >} >> >} >> >table ip6 libvirt_network { >> >chain forward { >> >type filter hook forward priority filter; policy accept; >> >counter packets 0 bytes 0 jump guest_cross >> >counter packets 0 bytes 0 jump guest_input >> >counter packets 0 bytes 0 jump guest_output >> >> And totally nothing with IPv6. >> > > As a bit of context, this is a virtlab machine whose primary purpose is to > run > kcli-based openshift clusters whose nodes are libvirt domains. Those are > the > "openshift-41[1-9]" networks and bridges. They are unrelated to the setup > I'm > looking into and most of them are actually obsolete (it's been years now > since > a 4.11 cluster last ran on the host :-)). > > My "guess" would be that the guest did not even get an IP address, maybe >> did not eve try DHCP. Are you sure the guest booted? >> > > I think it is, based on > > # virsh list > Id Name State > ------------------------------------------------- > [...] > 20 podvm-podsandbox-totok-8f10756a running > > But now that you mention it, I'm not positively sure that it tried DHCP. > The zero > traffic on the virbr0 bridge you mention above is overall explainable by > the domain > not having an address *but* if it did try DHCP those packets would show up > in the > virbr0 stats I guess? > > I did check out previously the DHCP leases on the 'default' network: > > # virsh net-dhcp-leases default > Expiry Time MAC address Protocol IP address Hostname Client ID > or DUID > > ----------------------------------------------------------------------------------- > > and there are none but that doesn't rule out any other failure in DHCP. > > The domain runs a peer pods podvm image which I don't have any control > over and > frankly am not familiar with. I assume that it does do DHCP to configure > its interfaces > but as the guest agent example shows my information about the image might > not be > always accurate. > I verified that the VM does do DHCP (there actually doesn't seem to be any other means for a podvm to get its network configured in peer pods). pvl > Is there a way to check if the domain attempts DHCP purely from the > libvirt side, just > using libvirt means? > > Thanks! > pvl >

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domain not getting IP address
by Pavel Mores 18 Sep '25

18 Sep '25

Hi, I'm examining a domain that's connected to the 'default' network # virsh net-dumpxml default <network connections='1'> <name>default</name> <uuid>c757baa7-2b31-4794-9dfb-0df384575602</uuid> <forward mode='nat'> <nat> <port start='1024' end='65535'/> </nat> </forward> <bridge name='virbr0' stp='on' delay='0'/> <mac address='52:54:00:37:b7:92'/> <ip address='192.168.122.1' netmask='255.255.255.0'> <dhcp> <range start='192.168.122.2' end='192.168.122.254'/> </dhcp> </ip> </network> using a device as follows: <interface type='network'> <mac address='52:54:00:ed:06:2e'/> <source network='default' portid='83db8ca9-baed-47f3-ba0d-1a967ee86aa5' bridge='virbr0'/> <target dev='vnet19'/> <model type='virtio'/> <alias name='net0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/> </interface> The domain is running but apparently without an IP address: # virsh domifaddr podvm-podsandbox-totok-8f10756a Name MAC address Protocol Address ------------------------------------------------------------------------------- The requisite host-side interfaces look good (to me anyway :-)): 10: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc htb state UP group default qlen 1000 link/ether 52:54:00:37:b7:92 brd ff:ff:ff:ff:ff:ff inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0 valid_lft forever preferred_lft forever [...] 35: vnet19: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master virbr0 state UNKNOWN group default qlen 1000 link/ether fe:54:00:ed:06:2e brd ff:ff:ff:ff:ff:ff inet6 fe80::fc54:ff:feed:62e/64 scope link proto kernel_ll valid_lft forever preferred_lft forever I can share more information about the setup if necessary but I'll stop here for now since I feel this must be just a simple stupid oversight on my part. Please let me know if you'd like to have additional info. Thanks in advance, pvl

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How to recover from "Display output is not active"
by Jeffrey Walton 11 Sep '25

11 Sep '25

Hi Everyone, I'm working on Ubuntu 22.04.5, amd64, fully patched. It provides QEMU 1:6.2+dfsg-2ubuntu6.26 and libvirt 8.0.0-1ubuntu7.11. The problem I am experiencing is, when the host machine blanks the monitor, I lose the display on the guest when I sit back down at the computer and wake the monitor. The error message (?) in the guest window is, "Display output is not active." The condition happens with both VIRTIO and VGA models. Also see <https://imgur.com/a/tEp73k2>. I have not found a workaround to stop it from happening or recover after it happens. I have to Force Off the VM and then restart the VM to the display back. My host power configuration is: disable sleep, suspend, hibernate and hybrid-sleep via systemd's systemctl. However, I allow the monitor to be turned off after 15 minutes of inactivity. My guest power configuration is whatever the distro provides. Based on my searching, others have experienced the problem. And one fellow says switching to the VGA model fixed it for him. (But no joy for me). Does anyone have any suggestions for a work around? Thanks in advance. (And my apologies if this is the wrong list). Jeff

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QNAP backup of virsh virtual machines and NFS shared drives for Plex, Subversion, Mailbox to OneDrive via rclone
by pjbondi＠systemdatabase.com 10 Sep '25

10 Sep '25

Hello virsh community. https://community.qnap.com/t/qnap-backup-of-virsh-virtual-machines-and-nfs-… Thank you so much for your help with my online virsh backup script. I've posted my script at the above address. I hope it helps someone protect their data. In my opinion, the script is an excellent implementation of --> https://libvirt.org/kbase/live_full_disk_backup.html https://www.worldbackupday.com/en

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List checkpoints
by francisco.garcia＠baculasystems.com 09 Sep '25

09 Sep '25

Hello, I'm using checkpoints to back up Libvirt domains. I'm using the "virsh backup-begin" tool and specifying the dombackup and checkpoint XML files. Everything works correctly (I perform full and incremental backups) without any issues. When I list the checkpoints using the "virsh checkpoint-list DOMAIN --parent --topological" tool, it correctly shows me the entire chain of full and incremental backups. However, when I perform a differential backup, setting the parent of that checkpoint to the last full checkpoint, I have problems when listing them. It tells me that the parent of the differential checkpoint is the last incremental checkpoint, instead of the full checkpoint. And I don't understand why, because when I perform the backup-begin, I specify the full checkpoint in the "incremental" label, and the bitmap generated from the disk is all the data from the full checkpoint on. I put the xmls that I used: FULL BACKUP: dombackup.xml: ``` <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <domainbackup mode="pull"> <server name="localhost" port="10809"/> <disks> <disk name="vda" type="file"> <scratch file="/tmp/libvirt-full-30-vda-debian12.scratch"/> </disk> <disk name="vdb" type="file"> <scratch file="/tmp/libvirt-full-30-vdb-debian12.scratch"/> </disk> </disks> </domainbackup> ``` checkpoint.xml ``` <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <domaincheckpoint> <name>Full-30-Debian12</name> <disks> <disk name="vda" bitmap="Full-30-Debian12" checkpoint="bitmap"/> <disk name="vdb" bitmap="Full-30-Debian12" checkpoint="bitmap"/> <disk name="sda" checkpoint="no"/> </disks> </domaincheckpoint> ``` -------------------------------------------------------- INCREMENTAL BACKUP: dombackup.xml ``` <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <domainbackup mode="pull"> <server name="localhost" port="10809"/> <incremental>Full-30-Debian12</incremental> <disks> <disk name="vda" type="file"> <scratch file="/tmp/libvirt-incremental-35-vda-debian12.scratch"/> </disk> <disk name="vdb" type="file"> <scratch file="/tmp/libvirt-incremental-35-vdb-debian12.scratch"/> </disk> </disks> </domainbackup> ``` checkpoint.xml ``` <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <domaincheckpoint> <name>Incremental-31-Debian12</name> <parent> <name>Full-30-Debian12</name> </parent> <disks> <disk name="vda" bitmap="Incremental-31-Debian12" checkpoint="bitmap"/> <disk name="vdb" bitmap="Incremental-31-Debian12" checkpoint="bitmap"/> <disk name="sda" checkpoint="no"/> </disks> </domaincheckpoint> ``` ----------------------------------------------------------------- DIFFERENTIAL BACKUP: dombackup.xml ``` <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <domainbackup mode="pull"> <server name="localhost" port="10809"/> <incremental>Full-30-Debian12</incremental> <disks> <disk name="vda" type="file"> <scratch file="/tmp/libvirt-differential-36-vda-debian12.scratch"/> </disk> <disk name="vdb" type="file"> <scratch file="/tmp/libvirt-differential-36-vdb-debian12.scratch"/> </disk> </disks> </domainbackup> ``` checkpoint.xml ``` <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <domaincheckpoint> <name>Differential-32-Debian12</name> <parent> <name>Full-30-Debian12</name> </parent> <disks> <disk name="vda" bitmap="Differential-32-Debian12" checkpoint="bitmap"/> <disk name="vdb" bitmap="Differential-32-Debian12" checkpoint="bitmap"/> <disk name="sda" checkpoint="no"/> </disks> </domaincheckpoint> ``` ----------------------------------------------------------------------- After apply several "virsh backup-begin" with these files: ``` virsh checkpoint-list debian12 --topological --parent Name Creation Time Parent -------------------------------------------------------------------------------------------------------------------------------- Full-30-Debian12 2025-07-09 17:08:31 +0200 Incremental-31-Debian12 2025-07-09 17:34:56 +0200 Full-30-Debian12 Differential-32-Debian12 2025-07-09 17:37:51 +0200 Incremental-31-Debian12 ``` I do not know why the parent of "Differential-32-Debian12" is "Incremental-31-Debian12" instead of "Full-30-Debian12". Any ideas?

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