udev
Rulesudev
is one of those pieces of Linux
that is fairly well
documented and not very well understood. This note isn't intended as
a general introduction to writing udev
rules, but, rather, a brief
introduction to the topic by way of specific example.
udev
?There are many clever uses for udev
documented on the Web, but
the most common use is to ensure that when you connect a device -
disk, tape, usb thumbdrive, camera... whatever - to a Linux
system, that device shows up with the same name every time.
Original Unix
derivatives had a static tree of devices the system
could support. This was encoded in the /dev
file tree hierarchy.
This was pretty inflexible in the face of devices being added- and
removed from the system as it ran. For this reason, modern device
handling in Linux
and most other Unix
derivatives is
dynamic - the content of /dev
changes to reflect the actual
state of the system as things get connected or disconnected. (Exactly
how this is done is outside the purpose of this document, but if you
care, investigate how the Linux /sys
filesystem works.)
While the example below is "cooked", it is very much rooted in real
world udev
applications. We want to do the following things:
- Identify a specific disk no matter what name it was assigned name under
/dev
.- Create a symbolic link to that disk so that - no matter what it's name under
/dev/
might be at the moment - the symbolic link is always the same.- Change the user and group ownership of that disk to something other than the default (
root:disk
).- Set specific permissions for the disk.
- Create a corresponding "raw" character device under
/dev/raw
associated with our disk above.
udev
Rules Live?Tim Daneliuk - tundra@tundraware.com
Comments and/or improvements welcome!
$Id: Deconstructing_Linux_udev_Rules.rst,v 1.105 2013/10/31 21:52:20 tundra Exp $
You can find the latest version of this document at:
http://www.tundraware.com/TechnicalNotes/Deconstructing-Linux-udev-Rules