Re: Learning about the Kernal

From	Rich <rich@example.invalid>
Newsgroups	comp.os.linux.misc
Subject	Re: Learning about the Kernal
Date	2015-03-22 15:13 +0000
Organization	My Linux Box
Message-ID	<memm6o$ba0$1@dont-email.me> (permalink)
References	(9 earlier) <mel14i$evu$14@reader1.panix.com> <mel1e8$ivr$1@dont-email.me> <melbtp$lov$1@reader1.panix.com> <melcd5$6b9$1@dont-email.me> <memfhu$f4e$1@reader1.panix.com>

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ruben safir <dont@email.me> wrote:
> On Sun, 22 Mar 2015 04:20:54 +0100, Aragorn wrote:

> >> The naming scheme was designed by individuals who want to drive people
> >> away from their computers.
> > 
> > That's not the point.

> my dear friend - that is the only point.  All the other ones you mention 
> are irrelevent.  /dev/sda1 MEANS something to the humans

Yes, it looks meaningful, at first glance.  But what you will learn as
you get to digging into the kernel internals is that while it looks
meaningful, it is not stable, because "sda1" is not permanently linked
to any one specific filesystem on any one specific piece of hardware. 
It is "1" only because it was the first disk partition assigned a
number by the kernel drivers.  So any stability it has is only because
if nothing changes in the hardware or software then the order in which
the hardware interfaces are assiged numbers remains stable.

What can, and will, happen is if you have plural physical disks, on
different hardware interfaces, and then you add one more disk, change
your motherboard, or change your kernal version, you will sometimes
encounter the result that the physical device partition that was sda1
is now assigned sdc3.  And your system will no longer boot because what
is now sda1 is not your root partition, and things come to a halt.

> UUID=22171af4-2b9c-4b5c-a53c-7cbb927f0a75 / reiserfs defaults 0 1
> is meaningless.

Yes, to the humans who did not not set it up, yes, it is meaningless. 
But it has the advantage of stability.  Because the UUID is actually
stored in the filesystem that is stored on the partition that is stored
on the physical hardware.  Because it is stored in the filesystem
itself, it no longer matters if the disk is named sda1 or sdb2 or sde5
by the kernel drivers, the filesystem that is the root filesystem will
always be mounted at the right spot.

This makes it safe to add additonal drives, upgrade to a new
motherboard, or upgrade to a new kernel. because doing any of those
things no longer has the risk of causing the sd?? numbers to be
randomly scrambled.

If you want to see who the sd?? devices are assigned to the UUID's, you
can look into the /dev/disk/by-* directories.  The by-uuid subdirectory
will tell you which UUID's is assigned which sd?? value.

Note that "plural disks" also has risk for someone with only a single
hard drive who happens to forgetfully leave a flash USB stick plugged
in.  Depending upon just exactly how their system behaves (kernel
drivers and hardware wise), that USB stick could become sda1 during a
reboot, pushing their old root partition over to sdb1, resulting in a
system that does not boot until they unplug the USB stick.

If they happen to have plural physical disks, then the USB stick, on
reboot, might become sdc1, pushing their old sdc1 to sdd1, and creating
problems of extra disks not being mounted where they belong (if at
all).

eSata interfaces present similar potential issues.

Thread

Learning about the Kernal ruben safir <ruben@mrbrklyn.com> - 2015-03-14 19:59 -0400
  Re: Learning about the Kernal Xavier Roche <xroche@free.fr.NOSPAM.invalid> - 2015-03-15 11:11 +0100
    Re: Learning about the Kernal ruben <nowhere@nowhere.nor> - 2015-03-15 21:14 +0000
      Re: Learning about the Kernal Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-03-16 10:02 +0200
        Re: Learning about the Kernal Ruben Safir <mrbrklyn@panix.com> - 2015-03-17 00:18 +0000
          Re: Learning about the Kernal Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2015-03-16 20:53 -0700
            Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-17 05:14 +0000
            Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-17 05:23 +0000
      Re: Learning about the Kernal Dan Espen <despen@verizon.net> - 2015-03-16 21:58 -0400
        Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-17 05:21 +0000
          Re: Learning about the Kernal Rich <rich@example.invalid> - 2015-03-17 10:51 +0000
          Re: Learning about the Kernal Dan Espen <despen@verizon.net> - 2015-03-17 09:10 -0400
            Re: Learning about the Kernal ruben safir <ruben@mrbrklyn.com> - 2015-03-17 14:12 -0400
              Re: Learning about the Kernal William Unruh <unruh@invalid.ca> - 2015-03-17 19:03 +0000
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-17 19:08 +0000
                Re: Learning about the Kernal Dan Espen <despen@verizon.net> - 2015-03-17 15:17 -0400
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-20 01:06 +0000
                Re: Learning about the Kernal Dan Espen <despen@verizon.net> - 2015-03-19 23:52 -0400
                Re: Learning about the Kernal Rich <rich@example.invalid> - 2015-03-20 10:52 +0000
                Re: Learning about the Kernal Jerry Peters <jerry@example.invalid> - 2015-03-20 20:33 +0000
                Re: Learning about the Kernal ruben safir <ruben@mrbrklyn.com> - 2015-04-20 09:48 -0400
              Re: Learning about the Kernal Dan Espen <despen@verizon.net> - 2015-03-17 15:08 -0400
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-18 03:36 +0000
                Re: Learning about the Kernal Dan Espen <despen@verizon.net> - 2015-03-18 10:09 -0400
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-20 01:04 +0000
                Re: Learning about the Kernal Rich <rich@example.invalid> - 2015-03-20 10:58 +0000
                Re: Learning about the Kernal Dan Espen <despen@verizon.net> - 2015-03-20 09:22 -0400
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-20 18:39 +0000
                Re: Learning about the Kernal Rich <rich@example.invalid> - 2015-03-20 20:04 +0000
                Re: Learning about the Kernal Dan Espen <despen@verizon.net> - 2015-03-20 21:10 -0400
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-21 05:03 +0000
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-20 18:42 +0000
                Re: Learning about the Kernal Dan Espen <despen@verizon.net> - 2015-03-20 15:31 -0400
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-21 05:13 +0000
                Re: Learning about the Kernal The Natural Philosopher <tnp@invalid.invalid> - 2015-03-21 09:13 +0000
                Re: Learning about the Kernal ruben <nowhere@nowhere.nor> - 2015-03-21 14:40 +0000
                Re: Learning about the Kernal Michael Black <et472@ncf.ca> - 2015-03-21 12:20 -0400
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-21 19:54 +0000
                Re: Learning about the Kernal Baho Utot <baho-utot@columbus.rr.com> - 2015-03-21 17:56 -0400
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-21 19:56 +0000
                Re: Learning about the Kernal Richard Kettlewell <rjk@greenend.org.uk> - 2015-03-21 16:18 +0000
          Re: Learning about the Kernal Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-03-17 16:10 +0200
            Re: Learning about the Kernal ruben safir <ruben@mrbrklyn.com> - 2015-03-17 14:06 -0400
              Re: Learning about the Kernal William Unruh <unruh@invalid.ca> - 2015-03-17 19:00 +0000
                Re: Learning about the Kernal Tim Watts <tw_usenet@dionic.net> - 2015-03-17 19:05 +0000
                Re: Learning about the Kernal Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2015-03-17 14:17 -0700
                Re: Learning about the Kernal William Unruh <unruh@invalid.ca> - 2015-03-19 06:04 +0000
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-21 08:45 +0000
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-21 08:20 +0000
                Re: Learning about the Kernal Rich <rich@example.invalid> - 2015-03-21 16:09 +0000
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-21 20:10 +0000
              Re: Learning about the Kernal Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-03-17 22:39 +0200
          Re: Learning about the Kernal Chick Tower <c.tower@deadspam.com> - 2015-03-18 03:35 +0000
            Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-21 08:47 +0000
              Re: Learning about the Kernal Jerry Peters <jerry@example.invalid> - 2015-03-21 20:19 +0000
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-21 20:30 +0000
                Re: Learning about the Kernal Jerry Peters <jerry@example.invalid> - 2015-03-22 20:05 +0000
                Re: Learning about the Kernal ruben safir <ruben@mrbrklyn.com> - 2015-03-23 01:16 -0400
                Re: Learning about the Kernal Jerry Peters <jerry@example.invalid> - 2015-03-23 20:27 +0000
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-25 02:57 +0000
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-25 02:59 +0000
                Re: Learning about the Kernal Jerry Peters <jerry@example.invalid> - 2015-03-25 20:59 +0000
                Re: Learning about the Kernal ruben safir <ruben@mrbrklyn.com> - 2015-04-20 09:44 -0400
                Re: Learning about the Kernal Aragorn <thorongil@telenet.be.invalid> - 2015-03-22 00:07 +0100
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-22 00:07 +0000
                Re: Learning about the Kernal Aragorn <thorongil@telenet.be.invalid> - 2015-03-22 01:13 +0100
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-22 03:11 +0000
                Re: Learning about the Kernal Aragorn <thorongil@telenet.be.invalid> - 2015-03-22 04:20 +0100
                Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-22 13:19 +0000
                Re: Learning about the Kernal Rich <rich@example.invalid> - 2015-03-22 15:13 +0000
                Re: Learning about the Kernal Aragorn <thorongil@telenet.be.invalid> - 2015-03-22 21:52 +0100
                Re: Learning about the Kernal Jerry Peters <jerry@example.invalid> - 2015-03-22 20:13 +0000
                Re: Learning about the Kernal Aragorn <thorongil@telenet.be.invalid> - 2015-03-22 22:01 +0100
              Re: Learning about the Kernal Chick Tower <c.tower@deadspam.com> - 2015-03-23 04:02 +0000
                Re: Learning about the Kernal Aragorn <thorongil@telenet.be.invalid> - 2015-03-23 05:13 +0100
                Re: Learning about the Kernal ruben <ceo@iran.gov> - 2015-04-12 13:03 +0000
      Re: Learning about the Kernal ruben safir <dont@email.me> - 2015-03-17 05:18 +0000
      Re: Learning about the Kernal ruben safir <ruben@mrbrklyn.com> - 2015-03-17 01:52 -0400

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