FreeBSD-5.3/sbin/devd/devd.8

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.\" Copyright (c) 2002 M. Warner Losh.
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.\" $FreeBSD: src/sbin/devd/devd.8,v 1.12 2004/07/07 19:57:14 ru Exp $
.\"
.Dd October 17, 2002
.Dt DEVD 8
.Os
.Sh NAME
.Nm devd
.Nd "device state change daemon"
.Sh SYNOPSIS
.Nm
.Op Fl Ddn
.Sh DESCRIPTION
The
.Nm
daemon provides a way to have userland programs run when certain
kernel events happen.
.Pp
The following options are accepted.
.Bl -tag -width indent
.It Fl D
Enable debugging messages.
.It Fl d
Run in the foreground instead of becoming a daemon.
.It Fl n
Do not process all pending events before becoming a daemon.
Instead, call daemon right away.
.El
.Sh IMPLEMENTATION NOTES
The
.Nm
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,
.Nm
will execute actions specified in
.Xr devd.conf 5 .
For example,
.Nm
might execute
.Xr dhclient 8
when an Ethernet adapter is added to the system, and kill the
.Xr dhclient 8
instance when the same adapter is removed.
Another example would be for
.Nm
to use a table to locate and load via
.Xr kldload 8
the proper driver for an unrecognized device that is added to the system.
.Pp
The
.Nm
utility
hooks into the
.Xr 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
.Nm .
Once
.Nm
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.
.Pp
The
.Nm
utility
reads
.Pa /etc/devd.conf
and uses that file to drive the rest of the process.
While the format of this file is described in
.Xr devd.conf 5 ,
some basics are covered here.
In the
.Ic options
section, one can define multiple directories to search
for config files.
All files in each of these directories are parsed.
These files are intended to be installed by third party vendors that
wish to hook into the
.Nm
system without modifying the user's other
config files.
.Pp
All messages that
.Nm
receives are forwarded to the
.Ux
domain socket at
.Pa /var/run/devd.pipe .
.Sh SEE ALSO
.Xr devctl 4 ,
.Xr devd.conf 5
.Sh AUTHORS
.An M. Warner Losh