=======================================================
Setting ownership of block devices in rhel6
=======================================================
:Title:        Setting ownership of block devices in rhel6
:Author:       Douglas O'Leary <dkoleary@olearycomputers.com>
:Description:  Setting ownership of block devices in rhel6
:Date created: 11/2013
:Date updated: 11/2013
:Disclaimer:   Standard: Use the information that follows at your own risk.  If you screw up a system, don't blame it on me...

Overview
=========

Google searches for how to update device permissions will lead to many hits
most of which contradict each other.  I found a very complete guide on the 
`archlinux wiki`_ 
which has a link pointing to `writing udev rules`_

.. _archlinux wiki: https://wiki.archlinux.org/index.php/Udev#About_udev_rules
.. _writing udev rules: http://www.reactivated.net/writing_udev_rules.html

Details:
========

* Rules notes (emphasis on data from the links above)
   - Rules are listed in /etc/udev/rules.d directory and are evaluated in order.
   - the '=' is for assignment, '==' is for evaluation.  This will be more clear
     a few lines

* Reading through those links above and others, you'll quickly realize that
  there are **alot** of options.  Fortunately, we don't need many.


+-------------------------+----------------------------------+
| Parameter               | Meaning                          |
+=========================+==================================+
| KERNEL=="sd*"           | applies to all sd devices        |
+-------------------------+----------------------------------+
| SUBSYSTEM=="block"      | applies to all block devices     |
+-------------------------+----------------------------------+
| ENV{DEVTYPE}=="disk"    | applies if device type is disk   |
+-------------------------+----------------------------------+
| ENV{ID_SERIAL}==${wwid} | applies if the wwid matches.     |
+-------------------------+----------------------------------+
| OWNER="hdp9adm"         | set the owner                    |
+-------------------------+----------------------------------+
| GROUP="hdp9adms"        | set the group                    |
+-------------------------+----------------------------------+
| MODE="0660"             | set the permissions              |
+-------------------------+----------------------------------+

*  An example of one entry in client defined rule file.  Line split for 
   readability only.  Ensure the rule is on one and only one line::

      # head -1 /etc/udev/rules.d/95\-hadoop\-disks.rules
      KERNEL=="sd*", SUBSYSTEM=="block", ENV{DEVTYPE}=="disk", \
      ENV{ID_SERIAL}=="3600605b005dd7110196075e3db43ed1c", \
      OWNER="hdp9adm", GROUP="hdp9adms", MODE="0660"

*  Where to get the wwid?  That's the subject of another ll entry: 
   :doc:`ID WWD for a LUN <linux_id_wwid_de_lun>`

Summary:
========

Like most things, this is easy if you know what you're doing.  **Finding**
consistent information was a bit of a challenge.  The process above seems
like the simplest approach.  Other approaches included running scripts from
within the rules files, etc.  Seems like overkill for the instance that I had
to support.