- Users - libvirt List Archives

virt-manager with SSH and 2FA with TOTP?
by Andreas Haumer 15 Apr '25

15 Apr '25

Hi! (I hope, this is the right list for my question. I already posted it to the debian-user ML, but someone pointed me to this list. Alas, there is no virt-manager ML anymore) In our network we have several Debian systems working as VM host running QEMU+KVM based virtual machines. I usually use virt-manager on my workstation as GUI to connect to the VM host, manage the VMs and also to connect to the VM console if needed. To connect to the VM host I use SSH with public key authentication. On the commandline with virsh this looks like this (example): andreas@ws1:~> virsh -c qemu+ssh://root@maxwell/system Welcome to virsh, the virtualization interactive terminal. Type: 'help' for help with commands 'quit' to quit virsh # So far, so good. Recently I decided to increase our internal network security standards and activated 2FA with time-based one-time passwords on several hosts. (The idea is to eventually have 2FA for SSH for all users on all hosts in our network) This works very well and even quite comfortable with authenticator-apps on my smartphone or KeePassXC on my workstation generating the TOTP. Example: andreas@ws1:~> ssh root@mach Enter OTP: Linux mach 6.1.0-32-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.129-1 (2025-03-06) x86_64 root@mach:~# So for a successful SSH connection I now have to enter a valid TOTP (generated by the authenticator app) and then it connects. Connecting to the host with virsh on the commandline also works in a similar way: andreas@ws1:~> virsh -c qemu+ssh://root@mach/system Enter OTP: Welcome to virsh, the virtualization interactive terminal. Type: 'help' for help with commands 'quit' to quit virsh # All fine. Works as designed... When I use virt-manager to connect to the VM host, the GUI opens a dialog asking for the OTP and then connects, showing the list of all configured VMs etc. I can also open the configuration of a given VM, manage and change it. All fine, too... But when I try to use virt-manager to connect to the console of a specific VM, it doesn't work as expected. virt-manager opens a new window for the console, but also endlessly keeps opening password entry dialogs. As soon as I enter the current OTP and klick "ok", another dialog is opened, again asking for another OTP. And so on... (These are one-time passwords, valid for 30 seconds, which cannot be re-used) I can connect to the VM console with a SPICE viewer like remmina using SSH port forwarding like this: andreas@ws1:~> ssh -L 5906:localhost:5906 root@mach Enter OTP: root@mach:~# (where 5906 is the SPICE port for the VM in question) And then use remmina to connect to port 5906 on localhost. This gives me the SPICE console of the VM. Of course, this is not as comfortable as using virt-manager. But with virt-manager I haven't found a way to successfully connect to the VM console with 2FA in place. So, finally, my question: Did anyone on this list manage to use virt-manager to connect to a VM console using SSH with 2FA? Thanks! - andreas -- Andreas Haumer *x Software + Systeme | mailto:andreas@xss.co.at Karmarschgasse 51/2/20 | https://www.xss.co.at/ A-1100 Vienna, Austria | Tel: +43-1-6060114

5 8

Is there any way to apply firewall rules to passt user mode networking?
by notsyncing＠163.com 12 Apr '25

12 Apr '25

Hello, I'm testing user mode network under session mode with libvirt and passt backend, and I found that the guest vm can access the whole host LAN(host is 192.168.1.2, guest ip configured to 192.168.100.2, but guest can access 192.168.1.3, which should not be allowed). Using firewalld dropping all traffic from guest ip has no effect at all. Is there any way to prevent guest accessing host LAN, while keeping guest's internet access? Thanks!

1 0

iptables rule affects vnet0?
by daggs 09 Apr '25

09 Apr '25

Greetings, I have a 2 vms on a host that can communicate with other hosts on the system. the two vms are connected by a virtsw0 bridge (vm1 and vm2) and on of the vms (vm1) has another connection (vnet0) to the host. it seems that the host can only communicate with the vm that has a direct connection to it and not the other vm (virtsw0 allows connection beteen both vms) here are the rules libvirt creates: -P INPUT ACCEPT -P FORWARD ACCEPT -P OUTPUT ACCEPT -N LIBVIRT_FWI -N LIBVIRT_FWO -N LIBVIRT_FWX -N LIBVIRT_INP -N LIBVIRT_OUT -A INPUT -j LIBVIRT_INP -A FORWARD -j LIBVIRT_FWX -A FORWARD -j LIBVIRT_FWI -A FORWARD -j LIBVIRT_FWO -A OUTPUT -j LIBVIRT_OUT -A LIBVIRT_FWI -o virsw0 -j REJECT --reject-with icmp-port-unreachable -A LIBVIRT_FWO -i virsw0 -j REJECT --reject-with icmp-port-unreachable -A LIBVIRT_FWX -i virsw0 -o virsw0 -j ACCEPT -A LIBVIRT_INP -i virsw0 -p udp -m udp --dport 53 -j ACCEPT -A LIBVIRT_INP -i virsw0 -p tcp -m tcp --dport 53 -j ACCEPT -A LIBVIRT_INP -i virsw0 -p udp -m udp --dport 67 -j ACCEPT -A LIBVIRT_INP -i virsw0 -p tcp -m tcp --dport 67 -j ACCEPT -A LIBVIRT_OUT -o virsw0 -p udp -m udp --dport 53 -j ACCEPT -A LIBVIRT_OUT -o virsw0 -p tcp -m tcp --dport 53 -j ACCEPT -A LIBVIRT_OUT -o virsw0 -p udp -m udp --dport 68 -j ACCEPT -A LIBVIRT_OUT -o virsw0 -p tcp -m tcp --dport 68 -j ACCEPT and here are the stats: Chain INPUT (policy ACCEPT 17405 packets, 1677K bytes) pkts bytes target prot opt in out source destination 17434 1688K LIBVIRT_INP all -- * * 0.0.0.0/0 0.0.0.0/0 Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 0 0 LIBVIRT_FWX all -- * * 0.0.0.0/0 0.0.0.0/0 0 0 LIBVIRT_FWI all -- * * 0.0.0.0/0 0.0.0.0/0 0 0 LIBVIRT_FWO all -- * * 0.0.0.0/0 0.0.0.0/0 Chain OUTPUT (policy ACCEPT 21058 packets, 3788K bytes) pkts bytes target prot opt in out source destination 21058 3788K LIBVIRT_OUT all -- * * 0.0.0.0/0 0.0.0.0/0 Chain LIBVIRT_FWI (1 references) pkts bytes target prot opt in out source destination 0 0 REJECT all -- * virsw0 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable Chain LIBVIRT_FWO (1 references) pkts bytes target prot opt in out source destination 0 0 REJECT all -- virsw0 * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable Chain LIBVIRT_FWX (1 references) pkts bytes target prot opt in out source destination 0 0 ACCEPT all -- virsw0 virsw0 0.0.0.0/0 0.0.0.0/0 Chain LIBVIRT_INP (1 references) pkts bytes target prot opt in out source destination 0 0 ACCEPT udp -- virsw0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:53 0 0 ACCEPT tcp -- virsw0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:53 29 10608 ACCEPT udp -- virsw0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:67 0 0 ACCEPT tcp -- virsw0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:67 Chain LIBVIRT_OUT (1 references) pkts bytes target prot opt in out source destination 0 0 ACCEPT udp -- * virsw0 0.0.0.0/0 0.0.0.0/0 udp dpt:53 0 0 ACCEPT tcp -- * virsw0 0.0.0.0/0 0.0.0.0/0 tcp dpt:53 0 0 ACCEPT udp -- * virsw0 0.0.0.0/0 0.0.0.0/0 udp dpt:68 0 0 ACCEPT tcp -- * virsw0 0.0.0.0/0 0.0.0.0/0 tcp dpt:68 is it possible I cannot access vm2 from the host because of the rules above? Thanks, Dagg

1 0

How to use microVM as a machine type?
by Qu Wenruo 08 Apr '25

08 Apr '25

Hi, Recently I'm hitting a bug related to edk2 that sometimes boot up can be very slow (before loading the bootloader): https://github.com/tianocore/edk2/issues/10765 It looks like the cause is the related to flash IOs. So I want to try using microVM machine type, as it's json file describes the device mapping is "memory", which should work around the slow boot. But I'm unable to setup a machine using microVM machine type in virtual-manager. And manually editing the xml file doesn't let me go any further, as VMM creates a default xml with ACPI feature, which is not supported by microVM. So I'm wondering, what's the proper way to use microVM machine type inside libvirt? Thanks, Qu

2 1

libvirt KVM virtual NIC as ens160 for running a virtual appliance designed for Vmware
by Sascha Frey 31 Mar '25

31 Mar '25

Hi, I want to run a virtual appliance which was designed for Vmware on libvirt Linux/KVM. Unfortunately, they hardcoded the kernel NIC name to ens160 inside that image. I can create a libvirt XML which creates a NIC recognised as ensXX, but not ens160, because libvirt doesn’t allow PCI slots over 0x1f. Is there any possible way to create a virtual NIC ens160 without modifying the image? Thanks.

2 1

Re: Capture pcap for each VM
by Laine Stump 31 Mar '25

31 Mar '25

(added users(a)lists.libvirt.org back into the Cc so that anyone else asking the same question in the future will benefit from the answer) On 3/28/25 8:12 AM, James Liu wrote: > Hi Laine, > > I tried your first solution but somehow it didn't work(the network is > NAT). I edited the xml in virt-manager gui. Whenever I added following > options, and click "Apply", the virt-manager will revert(remove) the > "alias" tag; consequently, the qemu command line couldn't find the > device name('foo' in this example). Sorry, I had meant to point this out but somehow forgot - user-specified aliases must begin with "ua-", otherwise they will be ignored. So instead of using "<alias name='foo'/>", use "<alias name='ua-foo'/>" (and then in the <qemu:arg value> use "netdev=hostua-foo") Also note that your guest should be shutdown while you're making these changes. > > Appreciate your suggestions. > > <interface type="network"> > <mac address="52:54:00:3a:bf:52"/> > <source network="default"/> > <model type="e1000e"/> > <alias name="*foo*"/> # virt-manager will always remove > this tag > <address type="pci" domain="0x0000" bus="0x01" slot="0x00" > function="0x0"/> > </interface> > > <qemu:commandline> > <qemu:arg value="-object"/> > <qemu:arg value="filter-dump,id=f1,netdev=*foo*,file=/tmp/xyzzy.pcap"/> > </qemu:commandline>

1 0

Clarifying isolated network rules in nftables
by Alexey Kashavkin 27 Mar '25

27 Mar '25

Hi, I’m trying to understand how firewall filter works for isolated network in libvirt v11.1.0. When I start the network I can see following rules in nftables: table ip 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 } chain guest_output { iif "virbr3" counter packets 0 bytes 0 reject } chain guest_input { oif "virbr3" counter packets 0 bytes 0 reject } chain guest_cross { iif "virbr3" oif "virbr3" counter packets 0 bytes 0 accept } chain guest_nat { type nat hook postrouting priority srcnat; policy accept; } } But when I start ping from one VM to another on the same isolated network, I don't see an increase in counters in either chain. In the libvirt code, I found a comment in src/network/network_nftables.c: /** * nftablesAddForwardAllowCross: * * Add a rule to @fw to allow traffic to go across @iface (the virtual * network's bridge) from one port to another. This allows all traffic * between guests on the same virtual network. */ But it seems that these rules don't work and are not needed. If I delete this table or some chains, nothing happens. VMs have connectivity with each other on this network. What are these rules for?

2 1

Capture pcap for each VM
by icefrog1950＠gmail.com 26 Mar '25

26 Mar '25

Hi, Is possible to capture pcaps for each VM individually? QEMU supports command line '-object filter-dump, file=test.pcap'. I'm not sure if Libvirt supports this features, or there are better ways to solve this. Many thanks.

2 1

Running DHCP server inside of the Guest VM instead of the host.
by gameplayer2019pl＠tutamail.com 26 Mar '25

26 Mar '25

Hello, I've recently tried to run KEA DHCP server inside of a Debian VM and the following host interface configuration, attached to that VM: ``` <network> <name>netasn-dhcpv6</name> <bridge name="netasn-dhcpv6" stp="on" delay="0"/> <mtu size="1500"/> <mac address="XX:XX:XX:XX:XX:XX"/> <dns enable="no"/> <ip family="ipv6" address="2a14:7581:feb::1" prefix="64"> </ip> </network> ``` But whenever I'm trying to run dhclient on another Debian VM attached to the same network I couldn't obtain the IPv6 lease from KEA DHCP. The host is as well running Debian, 12 version. Is there anyway to make the DHCP work from Guest VM instead of using built-in libvirt DHCP?

2 2

Integrating Open Virtual Network with Libvert Provisioned VMs
by odukoyaonline＠gmail.com 26 Mar '25

26 Mar '25

I am having a little confusion trying to integrate OVN defined networks(I tried with Ovs and it worked fine) with the VMs I have provisioned with Libvirt. I want to ask if there are resource around this and if not, will appreciate input from anyone who has a prior experience with it no matter how little.

1 0

General use of zstd instead of zlib compression
by Michael Niehren 17 Mar '25

17 Mar '25

Hi, currently i use on all VM's qcow2-Images with zlib compression. If i do an Backup, the Backup-Image will be compressed with zstd Level 3 to shrink the image for transfering it over not so fast internet connections. So, why not directly using zstd compression on the images. Are there any reason's not to do that ? As i always use virt-manager for administration, i patched qemu (V9.2.2) to create on default zstd compressed images (only 1 change in line 3525). So newly created images do have compression type zstd, which work's (qemi-img info). I see one unusual thing. If i do an qemi-img convert with compression_type=zstd the size of the converted image is much smaller than the original file while "qemu-img info" shows on both as compression type zstd. Do they use different compression levels, maybe ? If i now do an virsh backup-begin <domain>, the backup-Image does also has a bigger size than the original, while showing zstd as compression type (qemu-img info). If i convert it with the similar command as above, both converted images has nearly the same size. Even if i copy the smaller converted image to the original and boot the vm from the smaller image, the backup-image (after backup-begin) is bigger. So, i am confused. Are there any explanations about the different image sizes or what's going on here ? best regards Michael

3 10

live migration of SR-IOV vm
by Paul B. Henson 17 Mar '25

17 Mar '25

I have a vm using an sr-iov NIC that I'm testing live migration on (Debian 12, OS packages). Per the documentation, I have the sr-iov link set as transient with a pointer to the persistent virtio link: <interface type='network'> <mac address='52:54:00:a1:e0:38'/> <source network='sr-iov-intel-10G-1'/> <vlan> <tag id='400'/> </vlan> <model type='virtio'/> <teaming type='transient' persistent='ua-sr-iov-backup'/> <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/> </interface> and a persistent virto link down by default: <interface type='direct'> <mac address='52:54:00:a1:e0:38'/> <source dev='eno5np0.400' mode='bridge'/> <model type='virtio'/> <teaming type='persistent'/> <link state='down'/> <alias name='ua-sr-iov-backup'/> <address type='pci' domain='0x0000' bus='0x07' slot='0x00' function='0x0'/> </interface> The failover driver finds this in the vm: 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 100 0 3: eth1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel master eth0 state DOWN mode DEFAULT group default qlen 1000 10: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master eth0 state UP mode DEFAULT group default qlen 1000 and the network works fine. However, during migration, the sr-iov interface is removed, but the link on the virtio interface is *not* brought up: 2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000 3: eth1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel master eth0 state DOWN mode DEFAULT group default qlen 1000 resulting in no network for part of the migration. Once the box finished migrating, the replacement sv-iov link is plugged back in, and all is well once again: 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000 3: eth1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel master eth0 state DOWN mode DEFAULT group default qlen 1000 11: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master eth0 state UP mode DEFAULT group default qlen 1000 My understanding was that virsh migrate was supposed to automatically bring up the virtio link when the sr-iov link is removed? Or do I need to explicitly bring it up myself before the migration and take it down after? If I bring up the link manually before the migration, there are a few packets lost at that time, but then none are lost during the migration when the sr-iov link is pulled, or after the migration when I shut that link down again. Ideally no packets would be lost :), but I realize that's unlikely in practice... Thanks...

1 1

system cache dropped
by matus valentin 14 Mar '25

14 Mar '25

Hi, I have a setup with multiple virtual machines (VMs), each with a saved state. All VMs share the same parent, which is located on a shared drive. Whenever I restore any VM using virsh restore, the parent is dropped from the system cache, causing all data to be downloaded from the shared drive again. This results in unnecessary network traffic, even though the parent changes very rarely. However, if I create a child from the parent and call virsh create to create a new VM, the parent is never dropped from the system cache. Is this expected behavior? Should the parent be retained in the system cache during a virsh restore operation? Are there any configurations or settings that can prevent the parent from being dropped from the cache? thanks

1 0

best backup strategy for full backup's
by Michael Niehren 10 Mar '25

10 Mar '25

Hi together, actually i only do full-backup's of my virtual machines. I use the for the backup the "old" strategy: - virsh snapshot-create-as $vmname overlay --disk-only --atomic --no-metadata --quiesce - copy the qcow2 image file - virsh blockcommit $vmname $device --active --wait --pivot - the guest agent in the VM got's an 2 seconds freeze/thaw intervall Now i want to switch to the new strategy with "backup-begin". - virsh backup-begin $vmname - the guest agent does not got an freez/thaw signal As the guest agent got's no signal, is the backup over "backup-begin" still consistent ? Or do i have to be consistent to send an virsh domfsfreeze $vmname before starting the backup and an virsh domfsthaw $vmname it it is finished ? If so, the time intervall between freeze/thaw would be on an huge disk much more then 2 secords. So, is the old method currently still the better way, if only doing full-backup's ? best regards, Michael

2 6

So hey let's talk about this nftables ordering situation.
by robinleepowell＠gmail.com 25 Feb '25

25 Feb '25

So I, like many other people, have hit problems with nftables ordering, as has been discussed on this mailing list MANY TIMES. This whole thing seemed ridiculous so I asked the nftables people about what one is *supposed* to do in this situation. It turns out that the standard solution is for libvirt's nftables rules to set a packet mark (there's a collision possibility here but it's a 32 bit integer if you pick one at random it shouldn't be a problem) and then the user adds a rule to exclude packets with that mark from any reject rules they might have, or explicitly accept marked packets in their own chains, or whatever. It's not *as nice* as the iptables situation, but having documentation that says "if you're using nftables make sure that packets with mark 79892 are accepted in all your chains" is quite straightforward compared to the current situation of "LOL good luck". (I'm not blaming anyone there!, the current situation is impossible for libvirt to navigate and it's not anyone's fault.) If y'all don't like that, what's working excellently for me is adding `iifname "virbr*" accept` to my rule chain. FWIW. It was very hard to navigate through this situation because there's no documentation that this problem even exists. My suggestion is to describe the situation at https://libvirt.org/firewall.html and suggest the virbr* fix, and down the road maybe look at this mark thing. I'd like to help. I'm happy to write up issues for this, and I'm happy to write the updates to the firewall docs; just tell me what you'd like me to do.

4 8

nftables rules (DNS, DHCP, etc) not being written on Fedora 41
by robinleepowell＠gmail.com 21 Feb '25

21 Feb '25

I do not think this is any of the similar issues that have been posted to this list; I've checked. In particular, this in *NOT* an issue with nft rules precedence; the rules are simply not being written by libvirt. I'm running vagrant which is running libvirt on a Fedora 41 host. I do not think this is a vagrant problem, but if people want me to run virsh commands directly I certainly can. Anyway, vagrant was failing until I noticed that the default for /etc/libvirt/network.conf is now nftables, which I did not have set up. When I set `firewall_backend = "iptables"`, everything worked fine. I want to emphasize that: the same vagrant / libvirt setup *was* working with iptables. But I took that as a sign that it was time to move to nftables, so I moved everything on this host and stuff is back to working. But libvirt just isn't writing out the right nft rules. Like, at all. Here's the network vagrant creates: $ sudo virsh net-dumpxml vagrant-libvirt <network connections='1' ipv6='yes'> <name>vagrant-libvirt</name> <uuid>b2d93ef4-b305-4382-a380-c1eca92d8ebd</uuid> <forward mode='nat'> <nat> <port start='1024' end='65535'/> </nat> </forward> <bridge name='virbr1' stp='on' delay='0'/> <mac address='52:54:00:63:d3:f6'/> <ip address='192.168.121.1' netmask='255.255.255.0'> <dhcp> <range start='192.168.121.1' end='192.168.121.254'/> </dhcp> </ip> </network> And here's the *entire* libvirt-related ruleset in nftables: table ip 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 } chain guest_output { ip saddr 192.168.121.0/24 iif "virbr1" counter packets 0 bytes 0 accept iif "virbr1" counter packets 0 bytes 0 reject } chain guest_input { oif "virbr1" ip daddr 192.168.121.0/24 ct state established,related counter packets 0 bytes 0 accept oif "virbr1" counter packets 0 bytes 0 reject } chain guest_cross { iif "virbr1" oif "virbr1" counter packets 0 bytes 0 accept } chain guest_nat { type nat hook postrouting priority srcnat; policy accept; ip saddr 192.168.121.0/24 ip daddr 224.0.0.0/24 counter packets 1 bytes 187 return ip saddr 192.168.121.0/24 ip daddr 255.255.255.255 counter packets 0 bytes 0 return meta l4proto tcp ip saddr 192.168.121.0/24 ip daddr != 192.168.121.0/24 counter packets 0 bytes 0 masquerade to :1024-65535 meta l4proto udp ip saddr 192.168.121.0/24 ip daddr != 192.168.121.0/24 counter packets 0 bytes 0 masquerade to :1024-65535 ip saddr 192.168.121.0/24 ip daddr != 192.168.121.0/24 counter packets 0 bytes 0 masquerade } } 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 } chain guest_output { iif "virbr1" counter packets 0 bytes 0 reject } chain guest_input { oif "virbr1" counter packets 0 bytes 0 reject } chain guest_cross { iif "virbr1" oif "virbr1" counter packets 0 bytes 0 accept } chain guest_nat { type nat hook postrouting priority srcnat; policy accept; } } Here's some log output (I have virtnetworkd running with -v): $ sudo journalctl -u virtnetworkd.service | grep -i nft [snip] Feb 20 21:36:42 stodi.digitalkingdom.org virtnetworkd[89119]: using firewall_backend: 'nftables' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft list table ip libvirt_network' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft list table ip6 libvirt_network' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_output iif virbr1 counter reject' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_input oif virbr1 counter reject' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_cross iif virbr1 oif virbr1 counter accept' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip6 libvirt_network guest_output iif virbr1 counter reject' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip6 libvirt_network guest_input oif virbr1 counter reject' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip6 libvirt_network guest_cross iif virbr1 oif virbr1 counter accept' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_output ip saddr 192.168.121.0/24 iif virbr1 counter accept' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_input oif virbr1 ip daddr 192.168.121.0/24 ct state related,established counter accept' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat ip saddr 192.168.121.0/24 ip daddr '!=' 192.168.121.0/24 counter masquerade' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat meta l4proto udp ip saddr 192.168.121.0/24 ip daddr '!=' 192.168.121.0/24 counter masquerade to :1024-65535' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat meta l4proto tcp ip saddr 192.168.121.0/24 ip daddr '!=' 192.168.121.0/24 counter masquerade to :1024-65535' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat ip saddr 192.168.121.0/24 ip daddr 255.255.255.255/32 counter return' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat ip saddr 192.168.121.0/24 ip daddr 224.0.0.0/24 counter return' So it's not like trying to create the rules and failing, that I can see; it just isn't trying. To clarify this setup appears to be missing every rule that would be needed for DHCPv4 and DNS to work. Like https://gitlab.com/libvirt/libvirt/-/issues/88#note_694493261 shows rules for udp 67 and 53 that are just 100% not being created at all. I have no idea what's going wrong here or even where to look; the code at https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/GT75… sure *looks like* it should be unconditionally adding those rules. Help?

2 2

nftables rules (DNS, DHCP, etc) not being written on Fedora 41
by Robin Lee Powell 21 Feb '25

21 Feb '25

I do not think this is any of the similar issues that have been posted to this list; I've checked. In particular, this in *NOT* an issue with nft rules precedence; the rules are simply not being written by libvirt. I'm running vagrant which is running libvirt on a Fedora 41 host. I do not think this is a vagrant problem, but if people want me to run virsh commands directly I certainly can. Anyway, vagrant was failing until I noticed that the default for /etc/libvirt/network.conf is now nftables, which I did not have set up. When I set `firewall_backend = "iptables"`, everything worked fine. I want to emphasize that: the same vagrant / libvirt setup *was* working with iptables. But I took that as a sign that it was time to move to nftables, so I moved everything on this host and stuff is back to working. But libvirt just isn't writing out the right nft rules. Like, at all. Here's the network vagrant creates: $ sudo virsh net-dumpxml vagrant-libvirt <network connections='1' ipv6='yes'> <name>vagrant-libvirt</name> <uuid>b2d93ef4-b305-4382-a380-c1eca92d8ebd</uuid> <forward mode='nat'> <nat> <port start='1024' end='65535'/> </nat> </forward> <bridge name='virbr1' stp='on' delay='0'/> <mac address='52:54:00:63:d3:f6'/> <ip address='192.168.121.1' netmask='255.255.255.0'> <dhcp> <range start='192.168.121.1' end='192.168.121.254'/> </dhcp> </ip> </network> And here's the *entire* libvirt-related ruleset in nftables: table ip 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 } chain guest_output { ip saddr 192.168.121.0/24 iif "virbr1" counter packets 0 bytes 0 accept iif "virbr1" counter packets 0 bytes 0 reject } chain guest_input { oif "virbr1" ip daddr 192.168.121.0/24 ct state established,related counter packets 0 bytes 0 accept oif "virbr1" counter packets 0 bytes 0 reject } chain guest_cross { iif "virbr1" oif "virbr1" counter packets 0 bytes 0 accept } chain guest_nat { type nat hook postrouting priority srcnat; policy accept; ip saddr 192.168.121.0/24 ip daddr 224.0.0.0/24 counter packets 1 bytes 187 return ip saddr 192.168.121.0/24 ip daddr 255.255.255.255 counter packets 0 bytes 0 return meta l4proto tcp ip saddr 192.168.121.0/24 ip daddr != 192.168.121.0/24 counter packets 0 bytes 0 masquerade to :1024-65535 meta l4proto udp ip saddr 192.168.121.0/24 ip daddr != 192.168.121.0/24 counter packets 0 bytes 0 masquerade to :1024-65535 ip saddr 192.168.121.0/24 ip daddr != 192.168.121.0/24 counter packets 0 bytes 0 masquerade } } 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 } chain guest_output { iif "virbr1" counter packets 0 bytes 0 reject } chain guest_input { oif "virbr1" counter packets 0 bytes 0 reject } chain guest_cross { iif "virbr1" oif "virbr1" counter packets 0 bytes 0 accept } chain guest_nat { type nat hook postrouting priority srcnat; policy accept; } } Here's some log output (I have virtnetworkd running with -v): $ sudo journalctl -u virtnetworkd.service | grep -i nft [snip] Feb 20 21:36:42 stodi.digitalkingdom.org virtnetworkd[89119]: using firewall_backend: 'nftables' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft list table ip libvirt_network' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft list table ip6 libvirt_network' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_output iif virbr1 counter reject' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_input oif virbr1 counter reject' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_cross iif virbr1 oif virbr1 counter accept' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip6 libvirt_network guest_output iif virbr1 counter reject' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip6 libvirt_network guest_input oif virbr1 counter reject' Feb 20 21:36:46 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip6 libvirt_network guest_cross iif virbr1 oif virbr1 counter accept' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_output ip saddr 192.168.121.0/24 iif virbr1 counter accept' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_input oif virbr1 ip daddr 192.168.121.0/24 ct state related,established counter accept' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat ip saddr 192.168.121.0/24 ip daddr '!=' 192.168.121.0/24 counter masquerade' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat meta l4proto udp ip saddr 192.168.121.0/24 ip daddr '!=' 192.168.121.0/24 counter masquerade to :1024-65535' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat meta l4proto tcp ip saddr 192.168.121.0/24 ip daddr '!=' 192.168.121.0/24 counter masquerade to :1024-65535' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat ip saddr 192.168.121.0/24 ip daddr 255.255.255.255/32 counter return' Feb 20 21:36:47 stodi.digitalkingdom.org virtnetworkd[89119]: Applying 'nft -ae insert rule ip libvirt_network guest_nat ip saddr 192.168.121.0/24 ip daddr 224.0.0.0/24 counter return' So it's not like trying to create the rules and failing, that I can see; it just isn't trying. To clarify this setup appears to be missing every rule that would be needed for DHCPv4 and DNS to work. Like https://gitlab.com/libvirt/libvirt/-/issues/88#note_694493261 shows rules for udp 67 and 53 that are just 100% not being created at all. I have no idea what's going wrong here or even where to look; the code at https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/GT75… sure *looks like* it should be unconditionally adding those rules. Help?

1 0

Re: SEV-SNP Libvirt Support
by Michal Prívozník 17 Feb '25

17 Feb '25

On 2/17/25 11:11, Paraskevas Nik wrote: > Hello Michael, > Thanks for responding. I have built the libvirt and and then used ninja > install to install it. Does this also installs the correct selinux labels? Depends, if you've passed "-Dsystem=true" to meson setup then it should replace the system binaries and thus SELinux might have the correct policy. But otherwise, I'd suggest 'meson dist && rpmbuild -ta ...' and then installing those RPMs. Michal

2 1

SEV-SNP Libvirt Support
by Paraskevas Nik 17 Feb '25

17 Feb '25

Hello, I am trying to build libvirt v10.5.0 to support SEV-SNP but when I run virsh domcapabilities I am getting <sev support=no>. If I install libvirt 8.0.0 using apt install libvirt-daemon-system qemu-kvm them sev shows as supported. Everything is enabled on the system about SEV, SEV-ES, SEV-SNP. Is there a specific build option to enable SEV? *# cat /sys/module/kvm_amd/parameters/sev* *Y* *CPU: AMD EPYC 9254* *# dmesg | grep -i sev* *[ 0.000000] SEV-SNP: RMP table physical range [0x000000002d500000 - 0x000000004ddfffff]* *[ 0.009021] SEV-SNP: Reserving start/end of RMP table on a 2MB boundary [0x000000002d400000]* *[ 11.184492] ccp 0000:01:00.5: sev enabled* *[ 12.664210] ccp 0000:01:00.5: SEV API:1.55 build:36* *[ 12.664217] ccp 0000:01:00.5: SEV-SNP API:1.55 build:36* *[ 12.671343] kvm_amd: SEV enabled (ASIDs 16 - 1006)* *[ 12.671345] kvm_amd: SEV-ES enabled (ASIDs 1 - 15)* *[ 12.671346] kvm_amd: SEV-SNP enabled (ASIDs 1 - 15)* *Linux kernel version: 6.12**Libvirt version: 10.5.0* *qemu-system-x86_64 version : 9.1.0* *If you need any other information please let me know.Cheers*

2 1

Re: Network denied access
by Rodrigo Prieto 12 Feb '25

12 Feb '25

Thank you for taking the time to respond. I want to mention that I don't speak English, and it's difficult for me to understand using a translator. In the file */etc/libvirt/libvirtd.conf*, I have the following: access_drivers = [ "polkit" ] The *virtqemud* and *virtnetworkd* services are not installed. I used the version from the Debian 12 repositories. systemctl status virtnetworkd.socket Unit virtnetworkd.socket could not be found. systemctl status virtqemud.socket Unit virtqemud.socket could not be found. In the file */etc/libvirt/qemu.conf*, the default configuration is present. Best regards. El jue, 6 feb 2025 a las 20:48, Rodrigo Prieto (<rodrigoprieto2019(a)gmail.com>) escribió: > Thank you for taking the time to respond. I want to mention that I don't > speak English, and it's difficult for me to understand using a translator. > > In the file */etc/libvirt/libvirtd.conf*, I have the following: > access_drivers = [ "polkit" ] > > > The *virtqemud* and *virtnetworkd* services are not installed. I used the > version from the Debian 12 repositories. > > systemctl status virtnetworkd.socket > Unit virtnetworkd.socket could not be found. > > systemctl status virtqemud.socket > Unit virtqemud.socket could not be found. > > In the file */etc/libvirt/qemu.conf*, the default configuration is > present. > > Best regards. > > El jue, 6 feb 2025 a las 12:55, Martin Kletzander (<mkletzan(a)redhat.com>) > escribió: > >> On Fri, Jan 31, 2025 at 03:34:03AM -0300, Rodrigo Prieto wrote: >> >Hello, >> > >> >I am configuring Polkit using an example I found on the web. It correctly >> >displays the assigned domain for a given user, but when I try to start >> the >> >VM, I get the following error: >> > >> >error: Failed to start domain 'debian12' >> >error: access denied: 'network' denied access >> > >> >Here is my configuration: >> > >> >polkit.addRule(function(action, subject) { >> > if (action.id == "org.libvirt.unix.manage" && >> > subject.user == "lolo") { >> > return polkit.Result.YES; >> > } >> >}); >> >polkit.addRule(function(action, subject) { >> > if (action.id.indexOf("org.libvirt.api.domain.") == 0 && >> > subject.user == "lolo") { >> > if (action.lookup("connect_driver") == 'QEMU' && >> > action.lookup("domain_name") == 'debian12') { >> > return polkit.Result.YES; >> > } else { >> > return polkit.Result.NO; >> > } >> > } >> >}); >> > >> >> So doing this allows you to do anything with debian12 domain on the QEMU >> connection driver. >> >> >To grant network access, I have to configure the following: >> > >> >polkit.addRule(function(action, subject) { >> > if (action.id.indexOf("org.libvirt.api.network") == 0 && >> > subject.user == "lolo") { >> > return polkit.Result.YES; >> > } >> >}); >> > >> >> Adding this allows you to do anything with any network. This rule does >> omit a condition similar to the above one from the api.domain rule. >> >> >The problem with the previous configuration is that it allows full access >> >to the network, requiring the following configuration: >> > >> >> *to all the networks >> >> >polkit.addRule(function(action, subject) { >> > if ((action.id == "org.libvirt.api.network.stop" || >> > action.id == "org.libvirt.api.network.delete" || >> > action.id == "org.libvirt.api.network.write") && >> > subject.user == "lolo") { >> > return polkit.Result.NO; >> > } >> >}); >> > >> >By default, shouldn't network access behave like domains or pools, which >> >cannot be deleted? >> >> Can you not? The domain undefine API checks domain:delete ACL with the >> domain name and network undefine API checks network:delete ACL with the >> network name. I'll have to test it, but in the meantime could you try >> reproducing that with the same polkit rules (obviously modified to fit >> the domain/network difference)? >> >> >I tested it on Libvirt 9.0.0 and 10.0.0 >> > >> >> I did not find any difference between 9.0.0 and the current master with >> a quick git-fu. >> >> I tested it on current git master and it works fine, the user can >> undefine both the network and the domain, but only the one named as >> specified. >> >> >If you can help me, I would really appreciate it. >> >> Be sure to check that both virtqemud and virtnetworkd use polkit as >> their access driver in their respective configs. >> >> Have a nice day, >> Martin >> >

2 1

How can I control iptables/nftables rules addition on libvirtd host on Debian 12 ?
by oza.4h07＠gmail.com 10 Feb '25

10 Feb '25

Hello, When I install libvirt-daemon on a Debian 12 host, I can see the iptables rules below beeing added. *filter :INPUT ACCEPT [0:0] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] :LIBVIRT_FWI - [0:0] :LIBVIRT_FWO - [0:0] :LIBVIRT_FWX - [0:0] :LIBVIRT_INP - [0:0] :LIBVIRT_OUT - [0:0] -A INPUT -j LIBVIRT_INP -A FORWARD -j LIBVIRT_FWX -A FORWARD -j LIBVIRT_FWI -A FORWARD -j LIBVIRT_FWO -A OUTPUT -j LIBVIRT_OUT -A LIBVIRT_FWI -d 192.168.122.0/24 -o virbr0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT -A LIBVIRT_FWI -o virbr0 -j REJECT --reject-with icmp-port-unreachable -A LIBVIRT_FWO -s 192.168.122.0/24 -i virbr0 -j ACCEPT -A LIBVIRT_FWO -i virbr0 -j REJECT --reject-with icmp-port-unreachable -A LIBVIRT_FWX -i virbr0 -o virbr0 -j ACCEPT -A LIBVIRT_INP -i virbr0 -p udp -m udp --dport 53 -j ACCEPT -A LIBVIRT_INP -i virbr0 -p tcp -m tcp --dport 53 -j ACCEPT -A LIBVIRT_INP -i virbr0 -p udp -m udp --dport 67 -j ACCEPT -A LIBVIRT_INP -i virbr0 -p tcp -m tcp --dport 67 -j ACCEPT -A LIBVIRT_OUT -o virbr0 -p udp -m udp --dport 53 -j ACCEPT -A LIBVIRT_OUT -o virbr0 -p tcp -m tcp --dport 53 -j ACCEPT -A LIBVIRT_OUT -o virbr0 -p udp -m udp --dport 68 -j ACCEPT -A LIBVIRT_OUT -o virbr0 -p tcp -m tcp --dport 68 -j ACCEPT COMMIT For some reason, I need to add a couple of other rules. How can I do that ? Best regards

5 15

SEV Support Libvirt
by Paraskevas Nik 07 Feb '25

07 Feb '25

*Hello I am trying to enable libvirt to support sev-snp. Currently I am using virsh domcapabilities to check if its enabled but I am getting : <sev supported='no'/>* *Followed the instructions at : * *https://libvirt.org/kbase/launch_security_sev.html* <https://libvirt.org/kbase/launch_security_sev.html> * My AMD CPU supports SEV,SEV-SNP and I have followed all the steps and it is enabled. BIOS settings are configured to support SEV,SNP CPU: AMD EPYC 9254* *# cat /sys/module/kvm_amd/parameters/sev* *Y* *# dmesg | grep -i sev* *[ 0.000000] SEV-SNP: RMP table physical range [0x000000002d500000 - 0x000000004ddfffff]* *[ 0.009021] SEV-SNP: Reserving start/end of RMP table on a 2MB boundary [0x000000002d400000]* *[ 11.184492] ccp 0000:01:00.5: sev enabled* *[ 12.664210] ccp 0000:01:00.5: SEV API:1.55 build:36* *[ 12.664217] ccp 0000:01:00.5: SEV-SNP API:1.55 build:36* *[ 12.671343] kvm_amd: SEV enabled (ASIDs 16 - 1006)* *[ 12.671345] kvm_amd: SEV-ES enabled (ASIDs 1 - 15)* *[ 12.671346] kvm_amd: SEV-SNP enabled (ASIDs 1 - 15)* *Versions:* *Libvirt version: 10.7.0* *qemu-system-x86_64 version : 9.1.0* *Linux kernel version: 6.11.0-rc3* *Distro: Ubuntu 22.04.4 LTS* * If you need any other information please let me know.* Thanks!

2 1

Network denied access
by Rodrigo Prieto 06 Feb '25

06 Feb '25

Hello, I am configuring Polkit using an example I found on the web. It correctly displays the assigned domain for a given user, but when I try to start the VM, I get the following error: error: Failed to start domain 'debian12' error: access denied: 'network' denied access Here is my configuration: polkit.addRule(function(action, subject) { if (action.id == "org.libvirt.unix.manage" && subject.user == "lolo") { return polkit.Result.YES; } }); polkit.addRule(function(action, subject) { if (action.id.indexOf("org.libvirt.api.domain.") == 0 && subject.user == "lolo") { if (action.lookup("connect_driver") == 'QEMU' && action.lookup("domain_name") == 'debian12') { return polkit.Result.YES; } else { return polkit.Result.NO; } } }); To grant network access, I have to configure the following: polkit.addRule(function(action, subject) { if (action.id.indexOf("org.libvirt.api.network") == 0 && subject.user == "lolo") { return polkit.Result.YES; } }); The problem with the previous configuration is that it allows full access to the network, requiring the following configuration: polkit.addRule(function(action, subject) { if ((action.id == "org.libvirt.api.network.stop" || action.id == "org.libvirt.api.network.delete" || action.id == "org.libvirt.api.network.write") && subject.user == "lolo") { return polkit.Result.NO; } }); By default, shouldn't network access behave like domains or pools, which cannot be deleted? I tested it on Libvirt 9.0.0 and 10.0.0 If you can help me, I would really appreciate it.

2 1

Detect OS
by rodrigoprieto2019＠gmail.com 31 Jan '25

31 Jan '25

Hello, I would like to know if this behavior is normal. When I create a VM locally using the virt-install command with the argument --osinfo detect=on, it works perfectly and detects the operating system version. However, when I try to do it remotely using virt-install --connect=qemu+tcp://x.x.x.x/system, the following error appears: `--os-variant/--osinfo OS name is required, but no value was set or detected. This is now a fatal error. Specifying an OS name is required for modern, performant, and secure virtual machine defaults. If you expected virt-install to detect an OS name from the install media, you can set a fallback OS name with: --osinfo detect=on,name=OSNAME You can see a full list of possible OS name values with: virt-install --osinfo list If your Linux distro is not listed, try one of generic values such as: linux2024, linux2022, linux2020, linux2018, linux2016 If you just need to get the old behavior back, you can use: --osinfo detect=on,require=off Or export VIRTINSTALL_OSINFO_DISABLE_REQUIRE=1` Both the host machine and the client PC have osinfo updated to the latest version as of today. If I execute the command with --os-variant, it works correctly when done remotely. Is there a way to make it detect the operating system automatically when connected remotely? I’m using libvirtd (libvirt) 10.10.0 on Debian 12. Best regards, and thank you.

3 2

The right way to revert to external disk snapshots
by Alex Serban 29 Jan '25

29 Jan '25

Hello everyone, I'm seeking guidance on *best practices* for virtual machine recovery using external disk snapshots, particularly in a storage environment with ZFS. My current snapshot and recovery *workflow* involves: - Keeping VM disks & state on a ZFS volume; - Creating external KVM/Libvirt disk-only snapshots, resulting in deltas kept on the volume, next to the disk images; - Capturing the entire VM state through ZFS snapshots; - VM recovery through ZFS snapshot clones. I am particularly interested in obtaining an app-consistent recovery, in which I need to revert to the KVM snapshot of the VM, to ensure the possible clean state offered by a quiesced snapshot. Reading other posts from the archive and forums, it is clear for me that I cannot simply revert to the VM's snapshot, if it's a disk-only one, and that I have to manage them manually. Thus, my question is: *what is the best practice in order to recover the VM to the external disk snapshot that we have*? *What I have tried* and worked but I'm not sure is the best practice: on a VM with only one snapshot, I've changed the disk source files (which were pointing to deltas), to the ones pointed by their backingStore source files, effectively making them use the disk state of the snapshot time. This only works for shut-off VMs, as live VMs cannot have their disk sources changed, of course. Thus, for powered on VMs in the use case with only one snapshot, I've chosen to use `virDomainBlockPull` in order to have the app-consistent state pulled on the current disk (which was and still is pointing to the delta). *My concerns* on the approach I took regard, mostly, scalability and the safety of the whole process: - I am not sure how I could revert again to the current snapshot with the operations I did: for powered off VMs, disk images will change once we start using the VM, and for powered on VMs, the blockpull will alter the deltas which the disks were pointing to; - I don't see how I could apply this method in a scalable way, if the VM had more than one snapshot. At least for powered-on VMs. Thus, I thought I should seek some advice from you guys and see if there's another, smarter way that I can do this. Thanks a lot for your time, Alex Serban

2 3