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DEVD(8)			FreeBSD	System Manager's Manual		       DEVD(8)

     devd -- device state change daemon

     devd [-dnq] [-f file] [-l num]

     The devd daemon provides a	way to have userland programs run when certain
     kernel events happen.

     The following options are accepted.

     -d	      Run in the foreground instead of becoming	a daemon and log addi-
	      tional information for debugging.

     -f	file  Use configuration	file file instead of the default
	      /etc/devd.conf.  If option -f is specified more than once, the
	      last file	specified is used.

     -l	num   Limit concurrent socket connections to num.  The default connec-
	      tion limit is 10.

     -n	      Do not process all pending events	before becoming	a daemon.  In-
	      stead, call daemon right away.

     -q	      Quiet mode.  Only	log messages at	priority LOG_WARNING or	above.

     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	sys-
     tem, 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.  The	default	config file specifies /etc/devd	and
     /usr/local/etc/devd as directories	to search.  All	files in these direc-
     tories 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, for-
     warding all events	to any number of connected clients.  Clients connect
     by	opening	the SOCK_SEQPACKET UNIX	domain socket at

     /etc/devd.conf		   The default devd configuration file.
     /var/run/devd.seqpacket.pipe  The socket used by devd to communicate with
				   its clients.
     /var/run/devd.pipe		   A deprecated	socket retained	for use	with
				   old clients.

     devctl(4),	devd.conf(5)

     The devd utility first appeared in	FreeBSD	5.0.

     M.	Warner Losh

FreeBSD	13.0		       October 19, 2021			  FreeBSD 13.0


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