ACPITZ(4) Kernel Interfaces Manual ACPITZ(4)
acpitz -- ACPI Thermal Zone
acpitz* at acpi?
The acpitz driver supports so-called ACPI ``Thermal Zones''. The
temperature can be monitored by the envsys(4) API or the envstat(8)
The distinction between ``active'' and ``passive'' cooling is central to
the abstractions behind acpitz. These are inversely related to each
1. Active cooling means that the system increases the power
consumption of the machine by performing active thermal management
(for example, by turning on a fan) in order to reduce the
2. Passive cooling means that the system reduces the power
consumption of devices at the cost of system performance (for
example, by lowering the CPU frequencies) in order to reduce the
Only active cooling is currently supported on NetBSD.
It should be also noted that the internal functioning of these cooling
policies vary across machines. On some machines the operating system may
have little control over the thermal zones as the firmware manages the
thermal control internally, whereas on other machines the policies may be
exposed to the implementation at their full extent.
The acpitz driver knows about the active cooling levels, the current
temperatures, and critical, hot, and passive temperature thresholds (as
supported by the hardware). The driver is able to send events to
powerd(8) when the sensor's state has changed. When a Thermal Zone is
either critical or ``hot'', the /etc/powerd/scripts/sensor_temperature
script will be invoked with a critical-over event.
The critical temperature is the threshold for system shutdown. Depending
on the hardware, the mainboard will take down the system instantly and no
event will have a chance to be sent.
acpi(4), acpifan(4), envsys(4), envstat(8), powerd(8)
The acpitz driver appeared in NetBSD 2.0.
Jared D. McNeill <jmcneillATinvisible.ca>
While no pronounced bugs are known to exist, several caveats can be
o Passive cooling is not implemented.
o There is no user-controllable way to switch between active and
passive cooling, although the specifications support such transforms
on some machines.
o The ``hot'' temperature is a threshold in which the system ought to
be put into S4 sleep. This sleep state (``suspend to disk'') is not
supported on NetBSD.
NetBSD 6.1.5 January 9, 2011 NetBSD 6.1.5