The
devd
utility
is a system daemon that runs in the background all the time.
Whenever a device is added to or removed from the device tree,
devd
will execute actions specified in
devd.conf(5).
For example,
devd
might execute
dhclient(8)
when an Ethernet adapter is added to the system, and kill the
dhclient(8)
instance when the same adapter is removed.
Another example would be for
devd
to use a table to locate and load via
kldload(8)
the proper driver for an unrecognized device that is added to the system.
The
devd
utility
hooks into the
devctl(4)
device driver.
This device driver has hooks into the device configuration system.
When nodes are added or deleted from the tree, this device will
deliver information about the event to
devd.
Once
devd
has parsed the message, it will search its action list for that kind
of event and perform the action with the highest matching value.
For most mundane uses, the default handlers are adequate.
However, for more advanced users, the power is present to tweak every
aspect of what happens.
The
devd
utility
reads
/etc/devd.conf
or the alternate configuration file specified with a
-f
option and uses that file to drive the rest of the process.
While the format of this file is described in
devd.conf(5),
some basics are covered here.
In the
options
section, one can define multiple directories to search
for config files.
All files in these directories whose names match the pattern
*.conf
are parsed.
These files are intended to be installed by third party vendors that
wish to hook into the
devd
system without modifying the user's other
config files.
Since
devctl(4)
allows only one active reader,
devd
multiplexes it, forwarding all events to any number of connected clients.
Clients connect by opening the SOCK_SEQPACKET
Unix
domain socket at
/var/run/devd.seqpacket.pipe.
