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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
                    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

     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 clients.

     devctl(4), devd.conf(5)

     M. Warner Losh

FreeBSD 11.0-PRERELEASE         August 14, 2014        FreeBSD 11.0-PRERELEASE


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