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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 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. 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 gener- ation 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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