Proxmox VM missing CPU Flag for MongoDB installation

Problem

You want to install MongoDB, e.g. version 8.0, but it fails and you get warnings like e.g.:

"Your CPU is no longer officially supported by MongoDB themselves"

 

Cause

MongoDB requires CPUs with AVX (Advanced Vector Extensions) support. If your Proxmox VM is not configured to expose the hardware host CPUs AVX feature to the guest VM. The VM will report no AVX support and MongoDB may fail to run or use a non‑compatible binary.

Solution 

Source: https://forum.proxmox.com/threads/cpu-with-avx-support.146138/#post-716615 from iscrow from Oct 31, 2024:

My solution was to define a new CPU model based on x86-64-v2-AES that also exposes AVX

New models can be defined here cluster wide:
/etc/pve/virtual-guest/cpu-models.conf

Add this definition to the /etc/pve/virtual-guest/cpu-models.conf file:

cpu-model: x86-64-v2-AES-AVX
flags +avx;+avx2;+xsave;+aes;+popcnt;+ssse3;+sse4_1;+sse4_2
phys-bits host
hidden 0
hv-vendor-id proxmox
reported-model kvm64

It will then be immediately available in the GUI as a Custom (QEMU) CPU:


 

Example

1. Create /etc/pve/virtual-guest/cpu-models.conf on your proxmox system to create a new cpu-model
2. Put in the following lines:
   
   cpu-model: x86-64-v2-AES-AVX
flags +avx;+avx2;+xsave;+aes;+popcnt;+ssse3;+sse4_1;+sse4_2
phys-bits host
hidden 0
hv-vendor-id proxmox
reported-model kvm64
   
   
3. Select in the Proxmox GUI in the settings of the VM "x86-64-v2-AES-AVX" 
   or
   edit on the Proxmox CLI the conf-file of the VM /etc/pve/qemu-server/*VM ID*.conf and set cpu to custom-x86-64-v2-AES-AVX:
   
   root@prxmuc26:~#
root@prxmuc26:~# cat /etc/pve/qemu-server/202.conf
boot: order=scsi0;ide2;net0
cores: 1
cpu: custom-x86-64-v2-AES-AVX
ide2: local:iso/debian-13.3.0-amd64-netinst.iso,media=cdrom,size=754M
memory: 2048
meta: creation-qemu=10.1.2,ctime=1773517174
   
   
4. Reboot the VM
5. Check inside the VM the following commands to see if avx is available:
   
   debfad@VMdebUni:~$
debfad@VMdebUni:~$ grep -o -w 'avx' /proc/cpuinfo 
avx
debfad@VMdebUni:~$