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VMGENC(4) Kernel Interfaces Manual VMGENC(4) NAME vmgenc -- ACPI virtual machine generation ID counter SYNOPSIS device vmgenc 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. The hypervi- sor changes this identifier whenever the virtual machine is cloned, re- stored 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 dupli- cated virtual machines do not share cryptographic state. The driver also sends a devctl(4) event and an internal kernel notification so that other subsystems can respond to the duplication. 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. AUTHORS The vmgenc driver was written by Conrad Meyer <cem@FreeBSD.org>. This manual page was written by Christos Longros <chris.longros@gmail.com>. FreeBSD ports 15.quarterly March 21, 2026 VMGENC(4)
NAME | SYNOPSIS | DESCRIPTION | SYSCTL VARIABLES | SEE ALSO | HISTORY | AUTHORS
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