- 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

3 4

does the 'bandwidth' work?
by lejeczek 09 Oct '26

09 Oct '26

Hi guys. I have a network like so: <network> <name>10_1_1</name> <uuid>864fb78e-0fb0-4c32-bb47-0e5ac68d9491</uuid> <forward mode='bridge'/> <bridge name='nm-bridge1011'/> <bandwidth> <inbound average='610351' peak='620000'/> <outbound average='610351' peak='620000'/> </bandwidth> </network> I'd expect this to limit network to 10Gbs - since this is in kibibytes - I assume these two add to make the max? But when I _iperf3_ in guests then I get speeds near host's native, which are much higher than expected limit. Am I missing something - no <bandwidth> in guests - or there actually might be an issue here? I'm on Centos10 with libvirt-12.8.0-1.el10 thanks, L.

2 4

When libvirt would start dnsmasq?
by lejeczek 08 Oct '26

08 Oct '26

Hi guys. Under what circumstances libvrirt would start _dnsmasq_ on it's own? I certainly did not plan for libvirt to manage dhcp but sometimes I find: -> $ netstat -utapn | grep \:67 udp 0 0 0.0.0.0:67 0.0.0.0:* 19678/dnsmasq -> $ ps -Fp 19678 UID PID PPID C SZ RSS PSR STIME TTY TIME CMD dnsmasq 19678 1 0 2258 1824 8 Oct07 ? 00:00:00 /usr/sbin/dnsmasq --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro --dhcp-script=/usr/libexec/libvirt_leaseshelper which... does fcuk up my main (should be the only) DHCP server. Is it possible to tell libvirt not to do that no matter the circumstances? (or it's not libvirt?) many thanks, L.

3 4

Failed to unseal secret using TPM2
by lejeczek 30 Aug '26

30 Aug '26

Hi guys. Do you have some idea what is failing here: Starting virtsecretd.service - libvirt secret daemon... Failed to unseal secret using TPM2: Operation not permitted virtsecretd.service: Failed to set up credentials: Protocol error virtsecretd.service: Failed at step CREDENTIALS spawning /usr/sbin/virtsecretd: Protocol error virtsecretd.service: Main process exited, code=exited, status=243/CREDENTIALS virtsecretd.service: Failed with result 'exit-code'. Failed to start virtsecretd.service - libvirt secret daemon. I'm on Centos with libvirt-12.5.0-3.el10. Only think I can think of - this the only box out of few I have which updated - was EFI update via: -> $ fwupdmgr update After OS reboot this persists. I had to re-enrol LUKS keyslots which use TPM also, but that worked a ok, block devices unlock. Any/all suggestions/thoughts are much appreciated. Thanks.

1 1

Redirect guest COM port to host tty
by bd730c5053df9efb 25 Aug '26

25 Aug '26

Hi all! I have a slackware64-15.0 linux host running libvirt-11.10.0 with qemu 10.2.2 and a windows XP guest. I'm trying to have the gustes COM1 port redirected to the hosts /dev/ttyUSB0 device. I have not found a direct way of doing this in virt-manager since the only options for a serial device are "Output to a file", "Pseudo TTY" or a "UNIX socket". I have managed to modify the domains XML adding the following > <commandline xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'> > <arg value='-chardev'/> > <arg value='serial,path=/dev/ttyUSB0,id=hostserial0'/> > <arg value='-device'/> > <arg value='pci-serial,chardev=hostserial0'/> > </commandline> When I start the VM with this I get an error that says > Could not open '/dev/ttyUSB0': Operation not permitted I checked the device's permissions which are u+rw,g+rw and qemu is being executed with root permissions, I added o+rw to /dev/ttyUSB0 just in case but got the same error. I also tried with /dev/tty0 but got the same error. Thanks in advance! Best regards, Dave. Sent with Proton Mail secure email.

2 2

Libvirt/sanlock doesn't lock after a migration then trashes my disk.
by Matthew Schumacher 20 Aug '26

20 Aug '26

Hello All, Trying to figure out how this is supposed to work. I’m using pacemaker with the ocf:heartbeat:VirtualDomain to manage my virtual machines. If I start a vm on hyper-1 I get locks: > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerPluginGetDriver:275 : plugin=0x7f9b6003b080 > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerNew:298 : driver=0x7f9ba717d020 type=0 nparams=5 params=0x7f9bb00776c0 flags=0x0 > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerLogParams:96 : key=uuid type=uuid value=a5318b9d-48ea-4e06-8591-4f7826b3d0fa > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerLogParams:89 : key=name type=string value=testvm1 > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerLogParams:77 : key=id type=uint value=12 > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerLogParams:77 : key=pid type=uint value=7258 > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerLogParams:92 : key=uri type=cstring value=qemu:///system > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerAddResource:324 : lock=0x7f9ba8011280 type=0 name=/datastore/vm/testvm1/testvm1.raw nparams=0 params=(nil) flags=0x0 > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerAcquire:342 : lock=0x7f9ba8011280 state='<null>' flags=0x0 action=0 fd=(nil) > 2026-08-20 02:11:14.835+0000: 27626: debug : virLockManagerSanlockAcquire:1007 : Acquiring object 1 > 2026-08-20 02:11:14.845+0000: 27626: debug : virLockManagerSanlockAcquire:1057 : Acquire completed fd=-1 > 2026-08-20 02:11:14.845+0000: 27626: debug : virLockManagerFree:380 : lock=0x7f9ba8011280 If I move that VM to hyper-2 using (virsh --connect=qemu:///system --quiet migrate --live testvm1 qemu+ssh://hyper-2/system) it frees the lock on hyper-1: > 2026-08-20 02:11:32.485+0000: 27630: debug : virLockManagerPluginGetDriver:275 : plugin=0x7f9b6003b080 > 2026-08-20 02:11:32.485+0000: 27630: debug : virLockManagerNew:298 : driver=0x7f9ba717d020 type=0 nparams=5 params=0x7f9bae8744d0 flags=0x0 > 2026-08-20 02:11:32.485+0000: 27630: debug : virLockManagerLogParams:96 : key=uuid type=uuid value=a5318b9d-48ea-4e06-8591-4f7826b3d0fa > 2026-08-20 02:11:32.485+0000: 27630: debug : virLockManagerLogParams:89 : key=name type=string value=testvm1 > 2026-08-20 02:11:32.485+0000: 27630: debug : virLockManagerLogParams:77 : key=id type=uint value=12 > 2026-08-20 02:11:32.485+0000: 27630: debug : virLockManagerLogParams:77 : key=pid type=uint value=7258 > 2026-08-20 02:11:32.485+0000: 27630: debug : virLockManagerLogParams:92 : key=uri type=cstring value=(null) > 2026-08-20 02:11:32.486+0000: 27630: debug : virLockManagerAddResource:324 : lock=0x7f9b94069210 type=0 name=/datastore/vm/testvm1/testvm1.raw nparams=0 params=(nil) flags=0x0 > 2026-08-20 02:11:32.486+0000: 27630: debug : virLockManagerInquire:370 : lock=0x7f9b94069210 state=0x7f9b940656b0 flags=0x0 > 2026-08-20 02:11:32.486+0000: 27630: debug : virLockManagerSanlockInquire:1148 : pid=7258 > 2026-08-20 02:11:32.486+0000: 27630: debug : virLockManagerFree:380 : lock=0x7f9b94069210 > 2026-08-20 02:11:32.486+0000: 27630: debug : virLockManagerPluginGetName:259 : plugin=0x7f9b6003b080 > 2026-08-20 02:11:32.774+0000: 27628: debug : virLockManagerPluginUsesState:267 : plugin=0x7f9b6003b080 > 2026-08-20 02:11:33.028+0000: 7260: debug : virLockManagerPluginGetDriver:275 : plugin=0x7f9b6003b080 > 2026-08-20 02:11:33.028+0000: 7260: debug : virLockManagerNew:298 : driver=0x7f9ba717d020 type=0 nparams=5 params=0x7f9b9effc790 flags=0x0 > 2026-08-20 02:11:33.028+0000: 7260: debug : virLockManagerLogParams:96 : key=uuid type=uuid value=a5318b9d-48ea-4e06-8591-4f7826b3d0fa > 2026-08-20 02:11:33.028+0000: 7260: debug : virLockManagerLogParams:89 : key=name type=string value=testvm1 > 2026-08-20 02:11:33.028+0000: 7260: debug : virLockManagerLogParams:77 : key=id type=uint value=12 > 2026-08-20 02:11:33.028+0000: 7260: debug : virLockManagerLogParams:77 : key=pid type=uint value=7258 > 2026-08-20 02:11:33.028+0000: 7260: debug : virLockManagerLogParams:92 : key=uri type=cstring value=(null) > 2026-08-20 02:11:33.028+0000: 7260: debug : virLockManagerAddResource:324 : lock=0x7f9b60001590 type=0 name=/datastore/vm/testvm1/testvm1.raw nparams=0 params=(nil) flags=0x0 > 2026-08-20 02:11:33.028+0000: 7260: debug : virLockManagerRelease:358 : lock=0x7f9b60001590 state=0x7f9ba83df8d8 flags=0x0 > 2026-08-20 02:11:33.030+0000: 7260: debug : virLockManagerFree:380 : lock=0x7f9b60001590 Then on hyper-2 I get the lock: > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerPluginGetDriver:275 : plugin=0x7f4694043cd0 > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerNew:298 : driver=0x7f46be7e1020 type=0 nparams=5 params=0x7f46db6dc5f0 flags=0x0 > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerLogParams:96 : key=uuid type=uuid value=a5318b9d-48ea-4e06-8591-4f7826b3d0fa > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerLogParams:89 : key=name type=string value=testvm1 > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerLogParams:77 : key=id type=uint value=3 > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerLogParams:77 : key=pid type=uint value=17070 > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerLogParams:92 : key=uri type=cstring value=qemu:///system > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerAddResource:324 : lock=0x7f46cc006fb0 type=0 name=/datastore/vm/testvm1/testvm1.raw nparams=0 params=(nil) flags=0x0 > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerAcquire:342 : lock=0x7f46cc006fb0 state='__LIBVIRT__DISKS__:9ac7be7343fc02b995dcdfe541d0bcbc:/datastore/sanlock/9ac7be7343fc02b995dcdfe541d0bcbc:0:5' flags=0x0 action=0 fd=(nil) > 2026-08-20 02:11:33.057+0000: 3357: debug : virLockManagerSanlockAcquire:1007 : Acquiring object 1 > 2026-08-20 02:11:33.063+0000: 3357: debug : virLockManagerSanlockAcquire:1057 : Acquire completed fd=-1 > 2026-08-20 02:11:33.063+0000: 3357: debug : virLockManagerFree:380 : lock=0x7f46cc006fb0 All is well, but then I call on hyper-1 virsh create /datastore/vm/testvm1/testvm1.xml I get: error: internal error: QEMU unexpectedly closed the monitor (vm='testvm1'): 2026-08-20T02:12:28.413165Z qemu-system-x86_64: -device {"driver":"scsi-hd","bus":"scsi0.0","channel":0,"scsi-id":0,"lun":0,"device_id":"drive-scsi0-0-0-0","drive":"libvirt-2-storage","id":"scsi0-0-0-0","bootindex":2,"write-cache":"on"}: Failed to get "write” lock But in the logs I never see it checking the lock and while the NFS4.2 file system didn’t give it a lock and blocked, it still trashes the VM disk and the VM shows disk errors and mounts read-only. Shouldn’t libvirt/sanlock block this before starting qemu? I’m running libvirt 12.6.0 and qemu 10.2.4 on kernel 6.18.44. I would think these settings would work: # grep lock_ /etc/libvirt/qemu.conf lock_manager = "sanlock" # grep "^[^#]" /etc/libvirt/qemu-sanlock.conf auto_disk_leases = 1 disk_lease_dir = "/datastore/sanlock" host_id = 1 require_lease_for_disks = 1 Thanks!

1 0

File permissions in CIFS network filesystem pool
by Thomas Pircher 19 Aug '26

19 Aug '26

Hi, I'm trying to use a network filesystem pool on a Samba/CIFS share. Libvirt is configured with this pool: <pool type='netfs'> <name>netfs-default</name> <source> <host name='samba.lan.internal'/> <dir path='libvirt/default'/> <format type='cifs'/> </source> <target> <path>/var/lib/libvirt/images/netfs/default</path> <permissions> <mode>0755</mode> <owner>0</owner> <group>0</group> </permissions> </target> </pool> The Samba share is configured with: [libvirt] comment = VM storage pool browseable = yes path = /srv/datastore/samba/libvirt/ writeable = yes public = no guest ok = yes create mask = 0644 directory mask = 0755 force user = shared force group = +shared I can create the pool in virsh. The mounted files are owned by root on the libvirt machine. I can create and edit files as root if I access them via shell. However, libvirt can't start VMs. It fails to open the qcow2 file in the network filesystem pool with "permission denied". The libvirt host is Debian 14 (testing). I can't see any Selinux or Apparmor messages when the failure happens. So I believe the permissions problem is that libvirt tries to access the files as libvirt-qemu user, and this fails. I have tried adding the following snippet to the network fs pool definition, but after saving the pool, these options simply vanish from the network fs pool definition: <fs:mount_opts> <fs:option name='uid=libvirt-qemu'/> <fs:option name='gid=libvirt-qemu'/> </fs:mount_opts> So my question: how can I make this work? I have previously tried using NFSv4, but ran into similar issues. I guess I could make this work by mounting the share outside of libvirt and then point the filesystem pool at the mounted directory. Is there a more elegant way? Thanks, Thomas

2 2

Could not initialize refcount handling - efi ?
by lejeczek 17 Jul '26

17 Jul '26

Hi guys. I cannot start a domain - I wonder if the firmware, in xml, have anything to do with it or issue is different? Jul 17 11:07:41 virtqemud[5658]: Unable to read from monitor: Connection reset by peer Jul 17 11:07:41 virtqemud[5658]: internal error: QEMU unexpectedly closed the monitor (vm='ubusrv2'): 2026-07-17T09:07:41.089484Z qemu-kvm: -blockdev {"node-name":"libvirt-2-format","read-only":false,"discard":"unmap","cache":{"direct":true,"no-flush":false},"driver":"qcow2","encrypt":{"format":"luks","key-secret":"libvirt-2-format-encryption-secret0"},"file":"libvirt-2-storage","backing":null}: Could not initialize refcount handling: Input/output error Jul 17 11:07:41 virtqemud[5658]: internal error: process exited while connecting to monitor: 2026-07-17T09:07:41.089484Z qemu-kvm: -blockdev {"node-name":"libvirt-2-format","read-only":false,"discard":"unmap","cache":{"direct":true,"no-flush":false},"driver":"qcow2","encrypt":{"format":"luks","key-secret":"libvirt-2-format-encryption-secret0"},"file":"libvirt-2-storage","backing":null}: Could not initialize refcount handling: Input/output error Above happens with: <os firmware='efi'> <type arch='x86_64' machine='pc-q35-rhel10.2.0'>hvm</type> <firmware> <feature enabled='no' name='enrolled-keys'/> <feature enabled='yes' name='secure-boot'/> </firmware> <loader readonly='yes' type='pflash' format='raw'>/usr/share/edk2/ovmf/OVMF_CODE.secboot.fd</loader> <nvram template='/usr/share/edk2/ovmf/OVMF_VARS.fd' templateFormat='raw' format='raw'>/var/lib/libvirt/qemu/nvram/ubusrv2_VARS.fd</nvram> if I do not use EFI than domain starts, no above virtqemud errors, but guest does not boot, expectedly I think - I used to boot a ok. qemu-img shows no issues. Any thoughts? many thanks, L.

2 3

SELinux label with nvram?
by lejeczek 15 Jul '26

15 Jul '26

Hi guys. Having a domain like so: .... <os firmware='efi'> <type arch='x86_64' machine='pc-q35-rhel10.2.0'>hvm</type> <firmware> <feature enabled='yes' name='enrolled-keys'/> <feature enabled='yes' name='secure-boot'/> </firmware> <loader readonly='yes' secure='yes' type='pflash'>/usr/share/edk2/ovmf/OVMF_CODE.secboot.fd</loader> <nvram template='/usr/share/edk2/ovmf/OVMF_VARS.secboot.fd' templateFormat='raw' format='raw'>/var/lib/libvirt/qemu/nvram/ubusrv2_VARS.fd</nvram> ... <seclabel type='dynamic' model='selinux' relabel='yes'> <label>system_u:system_r:svirt_t:s0</label> <imagelabel>system_u:object_r:svirt_image_t:s0</imagelabel> </seclabel> <seclabel type='dynamic' model='dac' relabel='yes'> <label>+107:+107</label> <imagelabel>+107:+107</imagelabel> </seclabel> _seclabels_ are from virt-install - I'd presume this mandatory/default Any such domain - using NVRAM - fails to start with SELinux logging: ... virtqemud[1340835]: internal error: child reported (status=125): Requested operation is not valid: Setting different SELinux label on /var/lib/libvirt/qemu/nvram/ubusrv2_VARS.fd which is already in use ... Do you have any thoughts on how to "fix" it? I think I've seen this/similar issue a few years ago - I might have even filed a BZ. Also - I got a number of rpm updates among which is qemu to version 10.1.0-24 - prior to that my VMs worked a ok, on Centos 10. Anybody with similar experience? many thanks, L.

2 1

Extending sVirt to work under qemu:///session
by procmem＠riseup.net 07 Jun '26

07 Jun '26

Hi. I'm a developer with the security and privacy project; WhonixOS and recently we've ported our VMs to make use of the unprivileged qemu:///session mode to be compatible with our host OS that runs in a strict user only mode for daily activities. To my surprise, sVirt is not applied to VMs running in this mode. Inter VM isolation is important for our security model where traffic from an untrusted VM is forcefully tunneled to a trusted gateway VM running Tor to anonymize traffic. We don't want to be in a situation where we have to choose between running in the relatively riskier qemu:///system mode to gain the benefits of sVirt vs sacrificing sVirt inter VM isolation in order to be more compatible with our stricter unprivileged user implementation (which is just safer overall). Please consider extending sVirt to be compatible with qemu session for AppArmor and SELinux

1 0

How to use qemu's blkdebug driver (can't see backing device)
by Ian Pilcher 18 May '26

18 May '26

I am working on a disk burn-in utility, and I'd like to use qemu's blkdebug driver to simulate disk errors. I've added the qemu namespace to my domain. <domain xmlns:qemu="http://libvirt.org/schemas/domain/qemu/1.0" type="kvm"> I've set an alias for my SCSI controller. <controller type="scsi" index="0" model="virtio-scsi"> <driver queues="4" iothread="1"/> <alias name="ua-scsi0"/> <address type="pci" domain="0x0000" bus="0x07" slot="0x00" function="0x0"/> </controller> And I've added the qemu command-line options. <qemu:commandline> <qemu:arg value="-blockdev"/> <qemu:arg value="{"driver":"host_device","filename":"/dev/ram0","node-name":"ram-backend","cache":{"direct":true,"no-flush":false},"discard":"unmap"}"/> <qemu:arg value="-blockdev"/> <qemu:arg value="{"driver":"raw","file":"ram-backend","node-name":"raw-layer"}"/> <qemu:arg value="-blockdev"/> <qemu:arg value="{"driver":"blkdebug","config":"/var/lib/libvirt/images/test.conf","image":"raw-layer","node-name":"debug-disk"}"/> <qemu:arg value="-device"/> <qemu:arg value="scsi-hd,drive=debug-disk,id=scsi0-0-0-1,wwn=0x5000c50030000001,logical_block_size=4096,physical_block_size=4096,bus=ua-scsi0.0,channel=0,scsi-id=0,lun=1"/> </qemu:commandline> When I try to start the VM, I get this. Error starting domain: internal error: process exited while connecting to monitor: 2026-05-15T16:42:46.891789Z qemu-system-x86_64: -blockdev {"driver":"host_device","filename":"/dev/ram0","node-name":"ram-backend","cache":{"direct":true,"no-flush":false},"discard":"unmap"}: Could not open '/dev/ram0': No such file or directory /dev/ram0 definitely exists, and is owned by qemu:qemu. Google Gemini tells me that this is some sort of security feature, but it hasn't been able to suggest a non-janky way to work around it. (To me, changing the global libvirt configuration, rando trigger scripts, or creating some sort of redundant fake drive all fall into the janky category.) Is there really not a clean way to do this? -- ======================================================================== If your user interface is intuitive in retrospect ... it isn't intuitive ========================================================================

2 1

virt-viewer cage full screen tty issues
by Bram Diederik 08 May '26

08 May '26

my .profile is filled with scripts like this. pasted below. it allows a full screen desktop with out any other screens. at a dedicated tty. but it has two issues. If there already is an connection i need to kill everuthing on the tty. And sometimes when i pkill -9 -t tty9 switch from client system the keyboard and mouse dont work. they do work after i rebooted the VM. I dont google stuff deeply and make it my self if i cant find it right away. So i might be doing it wrong. anyway some one can help me with the two issues. ps one bash question. I have an exit. but a right placed ctrl C can break to prompt i dont want that does some one know how i always run the program or exit to logout state. Cheers. bram if [[ "$(tty)" == "/dev/tty10" ]]; then export XDG_RUNTIME_DIR=/run/user/$(id -u)/cage10 while true; do # start agent if needed [ -z "$SSH_AUTH_SOCK" ] && eval "$(ssh-agent -s)" >/dev/null # load key if needed ssh-add -l >/dev/null 2>&1 || ssh-add ~/.ssh/id_rsa mkdir -p "$XDG_RUNTIME_DIR" chmod 700 "$XDG_RUNTIME_DIR" # Run virt-viewer cage -s -- virt-viewer \ --domain-name vision \ -c "qemu+ssh://bram@jack/system?ssh_compression=yes" \ --attach -f \ --auto-resize=always sleep 2 done exit fi

1 0

virt-host-validate should warn about false positives
by therandshow＠gmail.com 04 May '26

04 May '26

virt-host-validate seems to sometimes complain about freezer support on machines with cgroups v2 where it doesn't matter, it also reports lack of devices cgroup if the user isn't running as root. Ideally, it should report N/A on freezer support for cgroups v2 or just PASS because it has validated that it wasn't necessary. Or maybe just have a warning at the bottom, failure for the freezer cgroup only applies to cgroups v1 For devices cgroup, a warning if the user is running not as root and the test fails, you may need elevated privileges to check cgroup 'devices' or something along those lines. Or failing to put it in the output, it would be nice if these facts were more prominent in a troubleshooting page

2 2

NVRAM storage live migration
by jchrist＠anexia-it.com 28 Apr '26

28 Apr '26

Hi, via virsh blockcopy I can live migrate disks between paths. Internally, this seems to use QEMU's drive-mirror or blockdev-mirror. Is something similar possible with the EFI NVRAM / vars file? blockcopy does not work, as judging by the code it only searches disk elements in the domain XML definition, which doesn't include single files like this. Under the hood, however, the vars file is represented in QEMU as a -blockdev. Judging by the docs for virDomainQemuMonitorCommand, it is unsafe to manually command QEMU to move this file around via drive-mirror and friends. Is there an alternative approach? Thanks, Jakob

1 0

Migrating VM to new supervisor - general question
by fc26wuqa＠studserv.uni-leipzig.de 20 Apr '26

20 Apr '26

Hello, I planned to move my VMs to a new (VM) supervisor, because I want to use another operation system for it. I am doubting myself, if this is such a good idea. When all my VMs are on different disks, can I just install a different OS on the root partition and just import the qcow2 files afterwards. Or am I risking losing my VMs/disks? I am a little bit afraid of messing it up... Thank you.

2 3

Windows 11 sound driver problem
by Owen Le Blanc 20 Apr '26

20 Apr '26

I have a Windows 11 system running under libvirt/qemu. A recent Microsoft software update overwrote the audio driver. Device manager would not let me install the one from the virtio ISO because it had determined that the "best driver was already installed". But sound wasn't working. I solved this by going into device manager and deleting the windows driver, then adding the viogpudo driver from the ISO manually. After rebooting the virtual machine, audio was working again. Yours, -- Owen Dr O V Le Blanc

1 0

attaching a specific usb device to vm
by daggs 20 Apr '26

20 Apr '26

Greetings, I have two identical hdd to usb enclosures connected to a server which run two vms, lets call the foo and goo. I'm looking for the ability to connect a specific hdd to a specific vm, naturally using vendor and device is not possible and using bus+port will provide what I need however it does not persists incase of port change. I saw that using the hooks, libvirt provides the xml to the hook and read it from the output of the hook. I tried adding detection and adding accurate hostdev xml tag to the vm xml and I see it from the output of the hook execution in the prepare stage however, the system boots but the hdd is not visible in guest. the docs reference this feature only for migrate and restore ops, does this means I cannot use it in the prepare stage? if so, is there another way to do what I want? Thanks, Dagg

3 4

LXC: net.unix.max_dgram_qlen
by Alexander Filatov 13 Apr '26

13 Apr '26

I want to set the sysctl net.unix.max_dgram_qlen parameter in LXC because the default value (10) is too small for me. Is it possible in some way without changing the source code of Linux kernel? I'm looking for the setting in XML configuration for an LXC domain and I can't find one. Setting it inside an LXC container (sysctl -w) is prohibited.

1 0

Questions about migrating VMs (with virt-manager)
by fc26wuqa＠studserv.uni-leipzig.de 09 Apr '26

09 Apr '26

Hello, I want to migrate multiple VMs to a new host. In the process, several questions came up, where I could not find an answer. I am using virt-manager version 1:5.0.0-5+deb13u1. I reordered and renamed my storage pools: When migrating a VM, how can I move the VM to a specific storage pool? Will the VM be moved to a storage pool with the same name by default? When migration finishes, the VM on the source host will still be accessible but will shut down. Is that true? Can I prevent the VM from shutting down during the migration? Thank you.

3 5

FYI: possible mailman service disruption 2026/04/08
by Daniel P. Berrangé 08 Apr '26

08 Apr '26

The hosting of the libvirt mailman instance will be moving to a new location tomorrow on 2026/04/08, at around 0900-1000 UTC. While we don't expect any significant loss of service, there could be minor short term, temporary disruption for sending emails while DNS records update. With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|

1 1

enable nested virtualization inside VM
by fc26wuqa＠studserv.uni-leipzig.de 31 Mar '26

31 Mar '26

Hello, I want to set up a NAT network inside a VM (so far as I understand, the name for that is nested virtualization). Unfortunately I only have Shell Access to the VM, and am not hosting it. I installed debian. The output of `uname -a`: Linux kvm1 6.12.74+deb13+1-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.74-2 (2026-03-08) x86_64 GNU/Linux When I run `kvm-ok` it says "INFO: Your CPU does not support KVM extensions KVM acceleration can NOT be used". When I try to load `kvm_intel` into the kernel (even with nested=1 option), it says "modprobe: ERROR: could not insert 'kvm_intel': Operation not supported". I can't start a network, there is no `/dev/kvm` device. I installed libvirt with `apt install --no-install-recommends qemu-system libvirt-clients libvirt-daemon-system`. Is there a way to enable libvirt support? For me, or the admins that host the VMs? Thank you.

2 4

double startup of sessioned vm causes user systemd service to fail
by daggs 11 Mar '26

11 Mar '26

Greetings, I'm running 3 vms in session mode on arch linux, I need each vm to startup on boot. libvirt version is 12.1.0. from what I understand, libvirt-guests lacks session support so I went to look and found that I can use per user systemd service, using this doc: https://wiki.archlinux.org/title/Systemd/User I defined each user to linger, created a service file and enabled it for each user. I've rebooted the machine and found out that not all the vms started, some of them have failed, each boot the outcome differs but usually there is atleast one vm which doesn't startup. I've check the status of the service and found that in the cases where the boot failed, the error was that the vm is already active, however virsh list shows ihe vm is off. none of the vms is marked as autostart. how can I find out who is the other source that starts up the vms? I assume it is something internal of libvirt. ideally, if possible, i'd like to use something from within libvirt or at least stop whatever autoboots the vms. Thanks, Dagg

1 0

Writeback vs default cache modes
by João Jandre 04 Mar '26

04 Mar '26

Hi, all I've been reading the QEMU documentation, the Libvirt documentation, as well as doing some testing and code investigation regarding disk cache modes. In the Libvirt documentation, it is stated that the disk driver cache modes accepted are "default", "none", "writethrough", "writeback", "directsync" and "unsafe". Analyzing the code, we can see that this is somewhat reflected on the cache modes that QEMU documents on the -drive option (https://qemu-project.gitlab.io/qemu/system/invocation.html) https://github.com/libvirt/libvirt/blob/04c1f458313e9001f5a804a898408e1f498… However, the default option (when we do not define the "cache" option) is different from other options and does not seem to map to any option on the Qemu side. I see that, from testing and analyzing the code, if the default (not defining the "cache" options) is used, cache.direct and cache.no-flush are not informed; also, the write-cache option is not informed. Just for comparison, here is a disk defined with cache=writeback: XML: |<disk type='file' device='disk'> <driver name='qemu' type='qcow2' cache='writeback'/> <source file='/mnt/a66f48f5-13c6-3676-b320-a15d32bbf32f/c0e925a9-6697-4ee9-8abf-d36c7a95cea4' index='2'/> <backingStore type='file' index='3'> <format type='qcow2'/> <source file='/mnt/a66f48f5-13c6-3676-b320-a15d32bbf32f/0db52809-9f33-43ac-8151-5452e9dee330'/> <backingStore/> </backingStore> <target dev='vda' bus='virtio'/> <serial>c0e925a966974ee98abf</serial> <alias name='virtio-disk0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </disk> | Generated QEMU command: |-blockdev {"driver":"file","filename":"/mnt/a66f48f5-13c6-3676-b320-a15d32bbf32f/c0e925a9-6697-4ee9-8abf-d36c7a95cea4","node-name":"libvirt-2-storage","cache":{"direct":false,"no-flush":false},"auto-read-only":true,"discard":"unmap"} -blockdev {"node-name":"libvirt-2-format","read-only":false,"cache":{"direct":false,"no-flush":false},"driver":"qcow2","file":"libvirt-2-storage","backing":"libvirt-3-format"} -device virtio-blk-pci,bus=pci.0,addr=0x5,drive=libvirt-2-format,id=virtio-disk0,bootindex=2,write-cache=on,serial=c0e925a966974ee98abf | And here is a disk that does not have the cache option: XML: |<disk type='file' device='disk'> <driver name='qemu' type='qcow2'/> <source file='/mnt/b59eff0f-5b97-37ed-a513-9e1983d1d19b/b430296b-0924-412e-a7b1-ddc3d4c90f83' index='2'/> <backingStore/> <target dev='vdc' bus='virtio'/> <serial>b430296b0924412ea7b1</serial> <alias name='virtio-disk2'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/> </disk> | Generated QEMU command: |blockdev {"driver":"file","filename":"/mnt/b59eff0f-5b97-37ed-a513-9e1983d1d19b/b430296b-0924-412e-a7b1-ddc3d4c90f83","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"} -blockdev {"node-name":"libvirt-2-format","read-only":false,"driver":"qcow2","file":"libvirt-2-storage","backing":null} -device virtio-blk-pci,bus=pci.0,addr=0x8,drive=libvirt-2-format,id=virtio-disk2,serial=b430296b0924412ea7b1 | The QEMU documentation states in the -drive option that the default cache mode is |Writeback| (see https://qemu-project.gitlab.io/qemu/system/invocation.html) so I expected that setting |Writeback| or |Default| as the cache mode on Libvirt would also be the same. I ran some performance tests using both options to try and verify if they were the same, but they are clearly different. For each of the configuration profiles below, I created a VM and ran some fio tests: Combination Disk cache mode Disk Controller IO thread IO policy hds0i default virtio-scsi 0 iouring hds0t default virtio-scsi 0 threads hds1i default virtio-scsi 1 iouring hds1t default virtio-scsi 1 threads hdv0i default virtio 0 iouring hdv0t default virtio 0 threads hdv1i default virtio 1 iouring hdv1t default virtio 1 threads wbs0i writeback virtio-scsi 0 iouring wbs0t writeback virtio-scsi 0 threads wbs1i writeback virtio-scsi 1 iouring wbs1t writeback virtio-scsi 1 threads wbv0i writeback virtio 0 iouring wbv0t writeback virtio 0 threads wbv1i writeback virtio 1 iouring wbv1t writeback virtio 1 threads The fio test results are in a html attached to the email. I would like to understand what the practical difference is between not informing the cache and any other option. I can see that the disk is defined in different way, but just by analyzing the code I was not able to understand what that leads to; also, looking at the performance tests, we clearly see a difference in the results. Would anyone be able to explain what is the expected behavior when the disk is defined in such a way? By the way, I'm using Libvirt 8.0.0 and Qemu 6.2.0. Best regards, João Jandre

3 2

How to properly modify xml in snapshot memory / managed save file
by wrangle 16 Feb '26

16 Feb '26

I am trying to move virtual machines to a new location on the same host. I want to preserve not only snapshots, but domain manage saved state as well as snapshot saved state. The xml is embedded in the snapshot and domain saved state and paths base image files are hard coded. I tried to sed replace the paths and necessary info, but it seems like libvirt expects the xml to be a certain length so it fails parsing. Parsing fails at different points of the embedded xml when I change the length of the path in the embedded xml. How can I properly edit the snapshot and domain managed saved state xml?

2 2

RBD pool not starting "An error occurred, but the cause is unknown"
by me＠vk4msl.com 16 Feb '26

16 Feb '26

Hi all, I've been battling this for about a year now. I've deployed virtual machine hosts running AlpineLinux 3.23 (recently updated from 3.21) which ships `libvirtd` 11.10.0, Ceph 19.2.3 and QEMU 10.1.3. (For reference: previous thread is archived at https://www.spinics.net/linux/fedora/libvirt-users/msg14421.html) I have two RBD pools defined: one is a "high availability" pool which replicates a copy of each block on every node, the other (previously used with OpenNebula) just makes sure there are at least 2 copies of blocks across the nodes (preferrably 3). They're called "ha-images" and "opennebula-images" respectively. "ha-images" starts without issue. It has a configuration like the following: ``` <pool type="rbd"> <name>ha-images</name> <uuid>6beab982-52b3-495b-a4a7-ab7ebb522ef5</uuid> <capacity unit="bytes">16003182362624</capacity> <allocation unit="bytes">184657756160</allocation> <available unit="bytes">6658209792000</available> <source> <host name="172.31.252.1" port="6789"/> <host name="172.31.252.2" port="6789"/> <host name="172.31.252.5" port="6789"/> <host name="172.31.252.6" port="6789"/> <host name="172.31.252.7" port="6789"/> <name>ha</name> <auth type="ceph" username="libvirt"> <secret uuid="c14a16b5-bba5-473a-ae9b-53a9a6b0a4e3"/> </auth> </source> </pool> ``` No issues with it, it starts just fine. "opennebula-images" never starts, its configuration: ``` <pool type="rbd"> <name>opennebula-images</name> <uuid>fcaa2fa8-f0d2-4919-9168-756a9f4ad7ee</uuid> <capacity unit="bytes">16003182362624</capacity> <allocation unit="bytes">7893286499025</allocation> <available unit="bytes">6658213388288</available> <source> <host name="172.31.252.1" port="6789"/> <host name="172.31.252.2" port="6789"/> <host name="172.31.252.5" port="6789"/> <host name="172.31.252.6" port="6789"/> <host name="172.31.252.7" port="6789"/> <name>one</name> <auth type="ceph" username="libvirt"> <secret uuid="c14a16b5-bba5-473a-ae9b-53a9a6b0a4e3"/> </auth> </source> </pool> ``` The `libvirt` user I created in Ceph is able to list the RBD pool: ``` lithium:~# rbd --id libvirt ls -p one | head gapmx-old-vda gapmx-old-vdb gapmx-testing-vda gapmx-testing-vdb gapmx-vda gapmx-vdb mastodon-vda mastodon-vdb mastodon-vdd mastodon-vde ``` Starting it, `libvirt` merely tells me: "An error occurred, but the cause is unknown". No logs written anywhere, no explanation. Just "computer says no". Yet, if I hand-configure my virtual machines, I can still mount RBD volumes as virtual disks within either pool. I just can't browse them via `virsh` or `virt-manager` on the `opennebula-images` pool like I can for the `ha-images` pool. Where should I be looking for the error? What did I do wrong that makes it refuse to start?

4 3