VMGENC(4)

okay so bestie, this is VMGENC(4) from the Kernel Interfaces Manual — the page for the ACPI virtual machine generation ID counter. It's short, it's iconic, and it's lowkey doing important security work. 💅✨

💖 NAME 💖

vmgenc — ACPI virtual machine generation ID counter 🎀

🌸 SYNOPSIS 🌸

Kernel config, bestie:

device vmgenc

And in loader.conf(5):

vmgenc_load="YES"

🦋 DESCRIPTION 🦋

The vmgenc driver provides support for the Virtual Machine Generation ID, a 128-bit unique identifier exposed by the hypervisor via ACPI. no cap.

The hypervisor changes this identifier whenever the virtual machine is cloned, restored from a snapshot, or otherwise duplicated.

When a generation ID change is detected, the vmgenc driver feeds the new identifier into the kernel entropy pool via random(4), ensuring that duplicated virtual machines do not share cryptographic state. literally the whole point, and it ate. 🔥

The driver also sends a devctl(4) event and an internal kernel notification so that other subsystems can respond to the duplication. teamwork makes the dream work. 🫶

fr fr, the Virtual Machine Generation ID specification is supported by QEMU, VMware ESXi, Microsoft Hyper-V, and Xen.

🔥 SYSCTL VARIABLES 🔥

The following variable is available:

• dev.vmgenc.%d.guid — the current cached VM generation counter as a 128-bit value. This value is updated each time the hypervisor signals a generation change.

👀 SEE ALSO 👀

acpi(4), random(4)

🎀 HISTORY 🎀

The vmgenc driver first appeared in FreeBSD 13.0. periodt.

👑 AUTHORS 👑

The vmgenc driver was written by Conrad Meyer <cem@FreeBSD.org>. 👑

This manual page was written by Christos Longros <chris.longros@gmail.com>. 🫶

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okay bye bestie — this page came from Debian and is dated March 21, 2026. mwah 💋✨