This is a FreeBSD 5.0 and later feature which does not exist in earlier versions.
During initial system startup, the boot loader(8) will read the device.hints(5) file. This file stores kernel boot information known as variables, sometimes referred to as “device hints”. These “device hints” are used by device drivers for device configuration.
Device hints may also be specified at the
Stage 3 boot loader prompt. Variables can be added using
set
, removed with unset
, and viewed
with the show
commands. Variables set in the
/boot/device.hints
file can be overridden here also. Device hints entered at
the boot loader are not permanent and will be forgotten on the next
reboot.
Once the system is booted, the kenv(1) command can be used to dump all of the variables.
The syntax for the /boot/device.hints
file is one variable per line, using
the standard hash “#” as comment markers. Lines are
constructed as follows:
hint.driver.unit.keyword="value
"
The syntax for the Stage 3 boot loader is:
set hint.driver.unit.keyword=value
driver
is the device driver name, unit
is the device driver unit number, and keyword
is the hint
keyword. The keyword may consist of the following options:
at
: specifies the bus which the device is attached to.
port
: specifies the start address of the I/O
to be used.
irq
: specifies the interrupt request number to be used.
drq
: specifies the DMA channel number.
maddr
: specifies the physical memory address occupied by the
device.
flags
: sets various flag bits for the device.
disabled
: if set to 1
the device is disabled.
Device drivers may accept (or require) more hints not listed here, viewing their manual page is recommended. For more information, consult the device.hints(5), kenv(1), loader.conf(5), and loader(8) manual pages.
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