systemd/udev.8

.TH UDEV 8 "October 2003" "" "Linux Administrator's Manual"
.SH NAME
udev \- Linux configurable dynamic device naming support
.SH SYNOPSIS
.BI udev " hotplug-subsystem"
.SH "DESCRIPTION"
.B udev
creates or removes device node files usually located in the /dev directory.
Its goal is to provide a dynamic device directory that contains only the files
for devices that are actually present.
.P
As part of the
.B hotplug
subsystem,
.B udev
is executed if a kernel device is added or removed from the system.
On device creation,
.B udev
reads the sysfs directory of the given device to collect device attributes
like label, serial number or bus device number.
These attributes are treated as a key 
to determine a unique name for device file creation.
.B udev
maintains a database for devices present on the system.
.br
On device removal,
.B udev
queries the internal database for the name of the device file to be deleted.
.SH "CONFIGURATION"
.B udev
expects its configuration at
.I /etc/udev/udev.config.
The file consists of a set of lines. All empty lines and
lines beginning with a '#' will be ignored.
.br
Every line defines the mapping between device attributes and the device file
name. It starts with a keyword defining the method used to match, followed by
one ore more keys to compare and the filename for the device. If no matching
configuration is found, the default kernel device name is used.
.P
The line format is:
.RS
.sp
.I method, key,[key,...] name
.sp
.RE
where valid methods with corresponding keys are:
.TP
.B LABEL
device label or serial number, like USB serial number, SCSI UUID or
file system label
.br
keys: \fBBUS\fP, \fIsysfs_attribute\fP
.TP
.B NUMBER
device number on the bus, like PCI bus id
.br
keys: \fBBUS\fP, \fBID\fP
.TP
.B TOPOLOGY
device position on bus, like physical port of USB device
.br
keys: \fBBUS\fP, \fBPLACE\fP
.TP
.B REPLACE
string replacement of the kernel device name
.br
key: \fBKERNEL_NAME\fP
.TP
.B CALLOUT
calling external program, that returns a string to match
.br
keys: \fBBUS\fP, \fBPROGRAM\fP, \fBID\fP
.P
The name field supports simple printf-like string subtitution:
.RS
.TP
.B %n
the "kernel number" of the device
for example, 'sda3' has a "kernel number" of '3'
.TP
.B %M
the kernel major number for the device
.TP
.B %m
the kernel minor number for the device
.TP
.B %b
the bus id for the device
.RE
.P
A sample \fIudev.conf\fP might look like this:
.sp
.nf
# USB printer to be called lp_color
LABEL, BUS="usb", serial="W09090207101241330", NAME="lp_color"

# sound card with PCI bus id 00:0b.0 to be called dsp
NUMBER, BUS="pci", ID="00:0b.0", NAME="dsp"

# USB mouse at third port of the second hub to be called mouse1
TOPOLOGY, BUS="usb", PLACE="2.3", NAME="mouse1"

# ttyUSB1 should always be called pda
REPLACE, KERNEL="ttyUSB1", NAME="pda"

# if /sbin/scsi_id returns "OEM 0815" device will be called disk1
CALLOUT, PROGRAM="/sbin/scsi_id" BUS="scsi", ID="OEM 0815" NAME="disk1"

# USB webcams to be called webcam0, webcam1, ...
LABEL, BUS="usb", model="WebCam Version 3", NAME="webcam%n"
.fi
.P
Permissions and ownership for the created device files may specified at
.I /etc/udev/udev.permissions.
The file consists of a set of lines. All empty lines and
lines beginning with a '#' will be ignored.
.br
Every line lists a device name followed by owner, group and permission mode. All values are separated by colons.
.sp
A sample \fIudev.permissions\fP might look like this:
.sp
.nf
#name:user:group:mode
ttyUSB1:root:uucp:0666
dsp1:::0666
.fi

.SH "FILES"
.nf
.ft B
.ft
/sbin/udev                           udev program
/etc/udev/*                          udev config and database files
/etc/hotplug.d/default/udev.hotplug  hotplug symlink to udev program
.fi
.LP
.SH "SEE ALSO"
.BR hotplug (8)
.PP
The
.I http://linux-hotplug.sourceforge.net/
web site.
.SH AUTHORS
.B udev
was developed by Greg Kroah-Hartman <greg@kroah.com> with much help from
Dan Stekloff <dsteklof@us.ibm.com> and many others.