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

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: ID WWD for a 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.