Guest Agent not running Windows Server 2025

G

goldsmith

Active Member
Apr 11, 2019
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0
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Hello, Team.

I encountered this problem, after installation the agent works for less than a day, I tried different versions 285,271,266 with all the same problem.
Windows Server 2025 Version 24H2 Build 26100.32860.

It is impossible to restart the service from the system; the entire operating system must be rebooted.

Config Proxmox
Code: 
proxmox-ve: 9.1.0 (running kernel: 7.0.2-4-pve)
pve-manager: 9.1.14 (running version: 9.1.14/7d542528ee1851f7)
proxmox-kernel-helper: 9.0.4
proxmox-kernel-7.0: 7.0.2-4
proxmox-kernel-7.0.2-4-pve-signed: 7.0.2-4
proxmox-kernel-6.17.13-9-pve-signed: 6.17.13-9
proxmox-kernel-6.17: 6.17.13-9
proxmox-kernel-6.17.2-1-pve-signed: 6.17.2-1
ceph-fuse: 19.2.3-pve2
corosync: 3.1.10-pve2
criu: 4.1.1-1
frr-pythontools: 10.6.1-1+pve2
ifupdown2: 3.3.0-1+pmx12
intel-microcode: 3.20251111.1~deb13u1
ksm-control-daemon: 1.5-1
libjs-extjs: 7.0.0-5
libproxmox-acme-perl: 1.7.1
libproxmox-backup-qemu0: 2.0.2
libproxmox-rs-perl: 0.4.1
libpve-access-control: 9.1.1
libpve-apiclient-perl: 3.4.2
libpve-cluster-api-perl: 9.1.5
libpve-cluster-perl: 9.1.5
libpve-common-perl: 9.1.12
libpve-guest-common-perl: 6.0.3
libpve-http-server-perl: 6.0.5
libpve-network-perl: 1.5.1
libpve-notify-perl: 9.1.5
libpve-rs-perl: 0.14.1
libpve-storage-perl: 9.0.18
libspice-server1: 0.15.2-1+b1
lvm2: 2.03.31-2+pmx1
lxc-pve: 7.0.0-1
lxcfs: 7.0.0-pve1
novnc-pve: 1.7.0-1
proxmox-backup-client: 4.2.0-1
proxmox-backup-file-restore: 4.2.0-1
proxmox-backup-restore-image: 1.0.0
proxmox-firewall: 1.2.2
proxmox-kernel-helper: 9.0.4
proxmox-mail-forward: 1.0.3
proxmox-mini-journalreader: 1.6
proxmox-offline-mirror-helper: 0.7.3
proxmox-widget-toolkit: 5.2.1
pve-cluster: 9.1.5
pve-container: 6.1.8
pve-docs: 9.1.4
pve-edk2-firmware: 4.2025.05-2
pve-esxi-import-tools: 1.0.1
pve-firewall: 6.0.4
pve-firmware: 3.18-3
pve-ha-manager: 5.2.3
pve-i18n: 3.7.1
pve-qemu-kvm: 11.0.0-2
pve-xtermjs: 6.0.0-1
qemu-server: 9.1.12
smartmontools: 7.5-pve2
spiceterm: 3.4.2
swtpm: 0.8.0+pve3
vncterm: 1.9.2
zfsutils-linux: 2.3.4-pve1

Config VM:
Code: 
agent: 1
bios: ovmf
boot: order=sata0;ide2;net0
cores: 8
cpu: x86-64-v2-AES
efidisk0: hs-ala-pmh-ds03:vm-168-disk-0,efitype=4m,ms-cert=2023k,pre-enrolled-keys=1,size=528K
hotplug: disk,network,usb,memory,cpu
ide2: none,media=cdrom
machine: pc-q35-11.0
memory: 16384
meta: creation-qemu=11.0.0,ctime=1779963536
name: vm
net0: e1000=BC:24:11:69:4F:28,bridge=vmbr120,firewall=1
numa: 1
onboot: 1
ostype: win11
sata0: hs-ala-pmh-ds03:vm-168-disk-1,size=200G
scsihw: virtio-scsi-single
smbios1: uuid=4771cadd-7c23-4af9-938e-259e7f0cc3c9
sockets: 2
vmgenid: e506f8db-a5b7-495f-b377-1078e339bb02
 
_gabriel said:
is during backup ?
Click to expand...
No, I don't backup virtual machines at all. That's why I want to figure this out, I have this problem on almost all of them WS 2025. Why does it freeze? The QEMU service can't be restarted; the entire operating system needs to be restarted.
 
_gabriel said:
have you tried with win 2022 ?
Click to expand...
Unfortunately, it is not possible to check the 2022 version since it is licensed for 2025. I still think there's something wrong with the operating system itself. But I haven't figured out how to figure it out yet.
 
Microsoft allows downgrade. you need to get media and product key yourself or ask your OEM manufacturer.
Media/Keys sources are not really relevant, proof of the original 2025 purchase is.
You can try the eval ISO to dig out. win11 eval ISO can be used too as they use same binaries, same build 26100.
is there a MS SQL running ?
btw, no problem here with two 2025 VMs since day one, 1 on PVE 9.2 + 1 on PVE 8.4.
 
_gabriel said:
Microsoft allows downgrade. you need to get media and product key yourself or ask your OEM manufacturer.
Media/Keys sources are not really relevant, proof of the original 2025 purchase is.
You can try the eval ISO to dig out. win11 eval ISO can be used too as they use same binaries, same build 26100.
is there a MS SQL running ?
btw, no problem here with two 2025 VMs since day one, 1 on PVE 9.2 + 1 on PVE 8.4.
Click to expand...
Yes, I know. The systems are productive, I can't experiment. There is no MS SQL server. But there is clearly a problem, either in the operating system or in the agent itself, which does not work correctly on the 2025 server.
 
Try any of these --

1. Disable Virtualization-Based Security (VBS) & Core Isolation
Windows Server 2025 aggressively enforces Core Isolation and Memory Integrity by default. This frequently conflicts with how the paravirtualized VirtIO serial driver handles memory buffers, leading to silent driver hangs.

Inside the Windows Server VM, go to Windows Security > Device Security > Core Isolation details.

Turn Memory Integrity to Off.

To fully disable VBS via the registry, run this command in an elevated PowerShell prompt:

PowerShell
Set-ItemProperty -Path "HKLM:\System\CurrentControlSet\Control\DeviceGuard" -Name "EnableVirtualizationBasedSecurity" -Value 0
Reboot the VM.

2. Adjust CPU Topology & Type
Your current VM config uses cpu: x86-64-v2-AES with sockets: 2 and cores: 8 (totaling 16 vCPUs).

The CPU Type: Newer Windows Server 2025 builds are highly optimized for modern microarchitectures and occasionally panic or drop paravirtualized communication queues under older x86-64-v2 profiles. If your physical CPU supports it, change this to host or at least x86-64-v3 to provide the guest OS with modern instruction sets.

The Sockets: Multiple physical sockets cause Windows to treat the layout as a multi-socket NUMA topology, adding substantial scheduling overhead. Unless you are running on a multi-socket motherboard and mapping exact physical layout, it is highly recommended to change this to 1 Socket and 8 (or 16) Cores.

3. Switch from SATA to VirtIO SCSI Single
Your configuration shows sata0 is being used for the main OS drive:

Plaintext
sata0: hs-ala-pmh-ds03:vm-168-disk-1,size=200G
scsihw: virtio-scsi-single
While this doesn't directly rule the guest agent, mixing the emulated SATA bus with virtio-scsi-single under Windows Server 2025 causes high I/O wait patterns during heavy operations, which can cause the serial communication channel to time out.

Install the VirtIO SCSI driver manually via Device Manager if it isn't loaded yet.

Detach sata0 in Proxmox, and reattach the disk as scsi0 with IO Thread enabled.

4. Pin a Stable VirtIO Driver Version
You noted testing versions 285, 271, and 266.

Avoid 0.1.285, as it has a documented bug regarding read errors and heavy I/O handling on Server 2025 VMs.

The most stable sweet spot for Server 2025 right now is virtio-win-0.1.271.

Clean installation step:

Uninstall the QEMU Guest Agent entirely via Windows Control Panel.

Open Device Manager, show hidden devices, and uninstall the VirtIO Serial Driver (checking the box to delete the driver software).

Mount the 0.1.271 ISO, run the virtio-win-guest-tools.exe installer fresh, and reboot the system.

Summary Checklist for Proxmox Config:
Try updating your VM configuration lines to look closer to this:

Plaintext
sockets: 1
cores: 8 (or your preferred core count)
cpu: host
scsi0: hs-ala-pmh-ds03:vm-168-disk-1,iothread=1,size=200G
Systems Thinker. Builder of Proximo - The Proxmox MCP you can hand the keys — VE + Backup Server + Mail Gateway + Datacenter Manager on one audited trust core (plan · prove · undo · diagnose). MCP + A2A
 
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