[Novalug] linux fundamentals (VEQ)

William Sutton william@trilug.org
Wed Mar 11 07:42:55 EDT 2015


It is also true that while you may be able to create the device with the 
appropriate major and minor numbers, permissions, etc., it may not work as 
expected.  For example, Oracle socket files in /tmp.  You can create them 
using command line tools all day long, and they will look correct, but 
Oracle refuses to use them.  How do I know?  I accidentally deleted some 
at $WORK.  We ended up having to restore them from backups.

William Sutton

On Wed, 11 Mar 2015, Jon LaBadie via Novalug wrote:

> On Tue, Mar 10, 2015 at 09:56:53PM -0400, Don E. Groves, Jr. via Novalug wrote:
>> On Tue, Mar 10, 2015 at 4:31 PM, Jon LaBadie via Novalug <
>> novalug@firemountain.net> wrote:
>>
>>>
>>> UNIX systems provided both block and character devices for the disk
>>> and partitions.  I don't see an equivalent in Linux, is there one?
>>>
>>> The char devices were call "raw" devices.  The only "raw" I have is
>>> hidrawX which I assume is a Human Interface Device, not a disk.
>>>
>>> Jon
>>>
>>
>>     In computing <http://en.wikipedia.org/wiki/Computing>, specifically
>> Unix-like operating systems, a *raw device* is a special kind
>>     of block device <http://en.wikipedia.org/wiki/Block_device> file that
>> allows accessing a storage device such as a hard disk drive
>>     directly, bypassing the operating system's caches and buffers (although
>> the hardware
>>     caches might still be used).
>>      .........
>>      On Linux raw devices were deprecated and scheduled for removal at one
>> point,
>>      because the O_DIRECT flag can be used instead. However, later the
>> decision was
>>      made to keep raw devices support since some software cannot use the
>> O_DIRECT
>>      flag. Raw devices simply open block devices as if the O_DIRECT flag
>> would have
>>      been specified. Raw devices are character devices (major number 162).
>>         See:  Wikipedia raw device <http://en.wikipedia.org/wiki/Raw_device>
>>
>>
>> So yes if a "raw device" for the device you want/need doesn't exist you can
>> always create it.
>> Or you can simply open the device with the O_DIRECT flag.
>>
>
> Thanks Don,
>
> I was unaware of the command raw and its ability to create raw devices.
>
> Jon
> -- 
> Jon H. LaBadie                  novalugml@jgcomp.com
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