xref: /freebsd-src/sbin/devd/devd.8 (revision fa9896e082a1046ff4fbc75fcba4d18d1f2efc19)

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.Dd October 19, 2021
.Dt DEVD 8
.Os
.Sh NAME
.Nm devd
.Nd "device state change daemon"
.Sh SYNOPSIS
.Nm
.Op Fl dnq
.Op Fl f Ar file
.Op Fl l Ar num
.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 ".Fl f Ar file"
.It Fl d
Run in the foreground instead of becoming a daemon and log additional information for debugging.
.It Fl f Ar file
Use configuration file
.Ar file
instead of the default
.Pa /etc/devd.conf .
If option
.Fl f
is specified more than once, the last file specified is used.
.It Fl l Ar num
Limit concurrent socket connections to
.Ar num .
The default connection limit is 10.
.It Fl n
Do not process all pending events before becoming a daemon.
Instead, call daemon right away.
.It Fl q
Quiet mode.
Only log messages at priority LOG_WARNING or above.
.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
or the alternate configuration file specified with a
.Fl f
option 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.
.Pp
In the
.Ic options
section, one can define multiple directories to search
for config files.
The default config file specifies
.Pa /etc/devd
and
.Pa /usr/local/etc/devd
as directories to search.
All files in these directories whose names match the pattern
.Pa *.conf
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
Since
.Xr devctl 4
allows only one active reader,
.Nm
multiplexes it, forwarding all events to any number of connected clients.
Clients connect by opening the SOCK_SEQPACKET
.Ux
domain socket at
.Pa /var/run/devd.seqpacket.pipe .
.Sh FILES
.Bl -tag -width ".Pa /var/run/devd.seqpacket.pipe" -compact
.It Pa /etc/devd.conf
The default
.Nm
configuration file.
.It Pa /var/run/devd.seqpacket.pipe
The socket used by
.Nm
to communicate with its clients.
.It Pa /var/run/devd.pipe
A deprecated socket retained for use with old clients.
.El
.Sh SEE ALSO
.Xr devctl 4 ,
.Xr devd.conf 5
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 5.0 .
.Sh AUTHORS
.An M. Warner Losh