DEVD(8)                    BSD 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
              additional 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
              connection limit is 10.

     -n       Do not process all pending events before becoming a daemon.
              Instead, 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 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

     /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

     devctl(4), devd.conf(5)

     The devd utility first appeared in FreeBSD 5.0.

     M. Warner Losh

BSD                              October 5, 2016                             BSD