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          Deconstructing_Linux_udev_Rules.rst
 ``udev`` 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.
 
.. NOTE::  The examples and descriptions below assume you
           are running as ``root``.  Most of the commands
           described will either return nothing or will not
           work at all unless you are ``root``.
introduction to the topic by way of specific example.  Most tutorials
on this subject only provide you with templates along the lines of
"Here's how to do <fill in the blank> with udev."  The approach here
is more about "here's why rules work the way they do".  Hopefully,
you'll find it useful.
 
 
  .. WARNING:: The examples and descriptions below assume you are
               running as ``root``.  Most of the commands described
               will either return nothing or will not work at all
               unless you are ``root``.
 
               Because you are ``root`` and are making device-level
               changes, you can wholly and completely Bugger Up your
               machine (it took me 6 years of graduate school to learn
               to use that term like a Real Computer Scientist (tm)).
 
               So ... do the smart thing.  Don't practice this stuff
               on machines that matter.  Better still, spin up some
               VMs and play with it there.
 
               You have been warned.  We do provide tech support for
               this stuff.  For ordinary work we charge the usual
               rates.  For fixing things you screwed up, $10,000/hour
               ... prepaid.
  
 
 
Why Bother With ``udev``?
=========================
    Here the use of the ``+=`` operator means something different.  It
    means, *"I am the final rule in this matter.  No subsequent rule
    can change this setting."* That's how we prevent rules that are
    read after us (ones with higher numbers in their name) from
    overriding what we want.
    overriding what we want.  For example, on at least one system
    I worked on, using ``GROUP=`` got overriden by a later
    default filesystem rule that always reset group ownership to
    ``disk``.  Using ``:=`` instead, fixed this.
 
    One other thing here: Notice the use of numeric values for ``UID``
    and ``GID``.  You *could* use the actual user- and group names
    here.  In fact, most ``udev`` tutorials show it this way.  It is a
 
Document Revision Information
=============================
 
``$Id: Deconstructing_Linux_udev_Rules.rst,v 1.111 2013/11/01 02:00:13 tundra Exp $``
``$Id: Deconstructing_Linux_udev_Rules.rst,v 1.112 2013/11/01 02:17:08 tundra Exp $``
 
You can find the latest version of this document at:
 
  http://www.tundraware.com/TechnicalNotes/Deconstructing-Linux-udev-Rules
 ``udev`` 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.
+.. NOTE::  The examples and descriptions below assume you
+           are running as ``root``.  Most of the commands
+           described will either return nothing or will not
+           work at all unless you are ``root``.
+introduction to the topic by way of specific example.  Most tutorials
+on this subject only provide you with templates along the lines of
+"Here's how to do <fill in the blank> with udev."  The approach here
+is more about "here's why rules work the way they do".  Hopefully,
+you'll find it useful.
+  .. WARNING:: The examples and descriptions below assume you are
+               running as ``root``.  Most of the commands described
+               will either return nothing or will not work at all
+               unless you are ``root``.
+               Because you are ``root`` and are making device-level
+               changes, you can wholly and completely Bugger Up your
+               machine (it took me 6 years of graduate school to learn
+               to use that term like a Real Computer Scientist (tm)).
+               So ... do the smart thing.  Don't practice this stuff
+               on machines that matter.  Better still, spin up some
+               VMs and play with it there.
+               You have been warned.  We do provide tech support for
+               this stuff.  For ordinary work we charge the usual
+               rates.  For fixing things you screwed up, $10,000/hour
+               ... prepaid.
 Why Bother With ``udev``?
 =========================
     Here the use of the ``+=`` operator means something different.  It
     means, *"I am the final rule in this matter.  No subsequent rule
     can change this setting."* That's how we prevent rules that are
     read after us (ones with higher numbers in their name) from
+    overriding what we want.
+    overriding what we want.  For example, on at least one system
+    I worked on, using ``GROUP=`` got overriden by a later
+    default filesystem rule that always reset group ownership to
+    ``disk``.  Using ``:=`` instead, fixed this.
     One other thing here: Notice the use of numeric values for ``UID``
     and ``GID``.  You *could* use the actual user- and group names
     here.  In fact, most ``udev`` tutorials show it this way.  It is a
 Document Revision Information
 =============================
+``$Id: Deconstructing_Linux_udev_Rules.rst,v 1.111 2013/11/01 02:00:13 tundra Exp $``
+``$Id: Deconstructing_Linux_udev_Rules.rst,v 1.112 2013/11/01 02:17:08 tundra Exp $``
 You can find the latest version of this document at:
   http://www.tundraware.com/TechnicalNotes/Deconstructing-Linux-udev-Rules

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