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Re: Grub Manual
- From: Les Mikesell <lesmikesell gmail com>
- To: For users of Fedora <fedora-list redhat com>
- Subject: Re: Grub Manual
- Date: Sat, 20 Oct 2007 10:25:22 -0500
William Case wrote:
I would like to object to your objection to my description of what
occurs with GRUB.
Grub doesn't 'find' partitions, you tell it where the one it will use is
from the bios perspective with the root (hdx,x) directive before
Grub's job is to find partitions and file systems; not to use them.
Whether GRUB finds, goes to, or loads stage 1.5 or stage 2 are moot
and/or pedantic points.
No it isn't. The point is that it won't find anything unless you told
it which drive and partition to use, and you have to do this from the
perspective of bios and in the grub terminology neither of which match
the Linux terminology. Move your boot drive to a different bios
location and see what happens.
The OP maintained and continues to maintain "There is nothing simple
about what Grub does. It is the tiny software that let us boot our Linux
or Windows operating systems". I was responding by saying, in plain
language, that it is in fact quite simple.
Grub in its own way is just a specialized very small Operating System
that has one job -- to load other full Operating Systems.
Your responses unnecessarily re-complicate an issue that can
conceptually be easily understood. Once the idea of a separate small
independent system is absorbed by a reader, then the peculiarities of
the GRUB operating system (I know it is never called that) can be
Nobody cares much about how/what grub does internally as long as it
works. What matters from the user/operator's perspective is how you
have to configure it so it will in fact work. And what you have to do
is learn a completely different way of describing disk locations than
anything you've used elsewhere. If you only boot from your first
partition on your first drive and blindly follow the examples of (hd0,0)
you may never see the problem. Try copying your /boot to some other
partition on some other drive and see what you have to do to make it
alternate between the versions. It's not impossible (as long as it's in
a place bios can see), but it's not obvious either.
Similarly, the fact that the viewable source configuration file may
reside within a Linux partition (eg /boot) does not limit GRUB's
independence from all OS's that exist on a given hard disk. As a matter
of necessary convenience it is made visible within a full operating
system so that it can be amended or changed before the next boot, but
nonetheless remains unconnected to that (Linux or other) Operating
System. It is easy to confuse the Grub operating system with the full
system (Linux or others)
Yes, that's exactly the point. To work with the files that grub will use
you must use the running OS conventions, but to tell grub about them you
must use grub notation to describe bios conventions.
And the missing piece is that you - or the distro-packaged scripts -
update those locations through the OS concepts of where that partition
is mounted. This part is OS/distro specific and doesn't have a lot to
do with grub.
That's the point. Why confuse the issue?
Confuse? The manual should be from the operator's perspective, not the
program that only sees one side. The operator/user doing the
configuration needs to know both the OS convention to place the files
and the grub/bios convention to initialize grub correctly. These things
are hidden in the fedora installer but not exposed or documented very
well. You are probably right that it doesn't belong in an os-agnostic
grub manual but rather in a fedora-grub-admin manual.
I have taken the time to respond here, because by your responses you
have touched on a point that has become important to me. I have spent
three years digging deeper and deeper into the functioning of computers
and Operating Systems, particularly the RedHat/Fedora version of Linux.
Always after hours and hours of digging through technical and often
pedantic descriptions, I find that a two or three sentence overview in
plain understandable language would have sufficed to let someone new to
a concept have a eureka moment. Then all the rest easily slides into
Yes, the missing pieces are how you find which drive bios will call 0x80
and 0x81 under most circumstances (which can be extremely difficult, and
in the case of raid1 you really want to also know how they will be
addressed if the primary boot device fails which will depend on a lot of
things), the fact that grub calls these hd0 and hd1, and any notion of
where these devices are mounted into the linux filesystem. There is a
program that tries to generate a device map for grub installs and I've
seen it work sometimes, sometimes not. Is there any documentation for
the mechanism that program uses and how to second-guess the results when
it is wrong?
lesmikesell gmail com
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