[gentoo-user] grub chainloader

[gentoo-user] grub chainloader

[Thufir]

I've read the GRUB documentation, but still don't understand why the
following worked:


localhost ~ #
localhost ~ # cat /boot/grub/grub.conf
default 0
timeout 30
splashimage=(hd1,0)/grub/splash.xpm.gz


title=Gentoo Linux
        root (hd1,0)
        kernel /kernel-genkernel-x86-2.6.19-gentoo-r5 root=/dev/ram0
init=/linuxrc ramdisk=8192 real_root=/dev/hdb3
        initrd /initramfs-genkernel-x86-2.6.19-gentoo-r5

title Fedora (2.6.21-1.3228.fc7)
        root (hd0,1)
        kernel /vmlinuz-2.6.21-1.3228.fc7 ro root=LABEL=/ rhgb quiet
        initrd /initrd-2.6.21-1.3228.fc7.img

localhost ~ #
localhost ~ # date
Tue Jul 17 22:48:12 UTC 2007
localhost ~ #



I would've thought that the chainloader +1 statement would be required
-- that's my experience at least.



-Thufir
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[gentoo-user] Re: grub chainloader

[»Q«]

In <news:bf6b6d5c0707171550sa74b587v3652ac2f00d3be8e@mail.gmail.com>,
Thufir <hawat.thufir@gmail.com> wrote:

>I've read the GRUB documentation, but still don't understand why the
>following worked:

[snip grub.conf]

>I would've thought that the chainloader +1 statement would be required
>-- that's my experience at least.

It's only needed if you're booting an unsupported (by grub) OS;  it
tells grub to just hand off to another bootloader.  The +1 tells grub
to load the first sector of the OS's partition, which is where the
other bootloader should be embedded.

As long as you're booting Linux kernels, you can just point grub at
them without using another bootloader.

-- 
»Q«

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Re: [gentoo-user] Re: grub chainloader

[Thufir]

Oh.  Why was the grub documentation not understandable like that?
maybe I misread it.  thanks for explaining!


-Thufir
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gentoo-user@gentoo.org mailing list

Re: [gentoo-user] Re: grub chainloader

[Iain Buchanan]

On Tue, 2007-07-17 at 18:12 -0500, »Q« wrote:
> In <news:bf6b6d5c0707171550sa74b587v3652ac2f00d3be8e@mail.gmail.com>,
> Thufir <hawat.thufir@gmail.com> wrote:
> 
> >I've read the GRUB documentation, but still don't understand why the
> >following worked:
> 
> [snip grub.conf]
> 
> >I would've thought that the chainloader +1 statement would be required
> >-- that's my experience at least.
> 
> It's only needed if you're booting an unsupported (by grub) OS;

no only unsupported OSs, you can chainload anything (bootable) such as
another linux distro, which has installed a bootloader into the
partition.  See how this guy booted 30+ OS's from grub:
http://www.justlinux.com/forum/showthread.php?threadid=134856

>   it
> tells grub to just hand off to another bootloader.  The +1 tells grub
> to load the first sector of the OS's partition, which is where the
> other bootloader should be embedded.
> 
> As long as you're booting Linux kernels, you can just point grub at
> them without using another bootloader.

you mean as long as grub understands the kernel and filesystem, you can
tell grub to load the kernel directly, with provided arguments.

I think :)

cya,
-- 
Iain Buchanan <iaindb at netspace dot net dot au>

Kevin:  Dad, the fish got away. 
Joe Swanson:  The hell it did. You get in there and you kick that fish's ass.

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Re: [gentoo-user] Re: grub chainloader

[Mick]

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On Wednesday 18 July 2007 01:02, Iain Buchanan wrote:
> On Tue, 2007-07-17 at 18:12 -0500, »Q« wrote:
> > In <news:bf6b6d5c0707171550sa74b587v3652ac2f00d3be8e@mail.gmail.com>,
> >
> > Thufir <hawat.thufir@gmail.com> wrote:
> > >I've read the GRUB documentation, but still don't understand why the
> > >following worked:
> >
> > [snip grub.conf]
> >
> > >I would've thought that the chainloader +1 statement would be required
> > >-- that's my experience at least.
> >
> > It's only needed if you're booting an unsupported (by grub) OS;
>
> no only unsupported OSs, you can chainload anything (bootable) such as
> another linux distro, which has installed a bootloader into the
> partition.  See how this guy booted 30+ OS's from grub:
> http://www.justlinux.com/forum/showthread.php?threadid=134856
>
> >   it
> > tells grub to just hand off to another bootloader.  The +1 tells grub
> > to load the first sector of the OS's partition, which is where the
> > other bootloader should be embedded.
> >
> > As long as you're booting Linux kernels, you can just point grub at
> > them without using another bootloader.
>
> you mean as long as grub understands the kernel and filesystem, you can
> tell grub to load the kernel directly, with provided arguments.
>
> I think :)

If you have some reason not to mix one OS', or distro's boot files, kernels, 
etc with another, plus if you want to try a different version of grub then 
you can install grub separately in the new OS partition (instead of the MBR) 
and chainload this from your primary grub installation.  Should you wish to 
remove the new OS at a later date, you will not need to rummage through the 
primary OS' /boot to clean out redundant kernel images and what not.

Otherwise, as already mentioned, Grub will boot natively all Linux distros.
-- 
Regards,
Mick

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Re: [gentoo-user] Re: grub chainloader

[Alan McKinnon]

On Wednesday 18 July 2007, Thufir wrote:
> Oh.  Why was the grub documentation not understandable like that?
> maybe I misread it.  thanks for explaining!

The grub man pages are, ahem, skimpy. IIRC it's all of three paragraphs.

The full story is in the info pages, but the way they are written pretty 
much requires that you do go through all of it in sequence. And they 
are also written with the assumption that the reader understands the 
confines a boot loader has to work in.

alan



-- 
Optimists say the glass is half full,
Pessimists say the glass is half empty,
Developers say wtf is the glass twice as big as it needs to be?

Alan McKinnon
alan at linuxholdings dot co dot za
+27 82, double three seven, one nine three five
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Re: [gentoo-user] Re: grub chainloader

[Etaoin Shrdlu]

On Wednesday 18 July 2007 14:18, Alan McKinnon wrote:

> On Wednesday 18 July 2007, Thufir wrote:
> > Oh.  Why was the grub documentation not understandable like that?
> > maybe I misread it.  thanks for explaining!
>
> The grub man pages are, ahem, skimpy. IIRC it's all of three
> paragraphs.
>
> The full story is in the info pages, but the way they are written
> pretty much requires that you do go through all of it in sequence.

You can get everything at once and in the same place using the online 
docs:

http://www.gnu.org/software/grub/manual/grub.html


> And they are also written with the assumption that the reader
> understands the confines a boot loader has to work in.

This is still true with the online docs of course, since the docs are 
essentially the same.
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Re: [gentoo-user] Re: grub chainloader

[Александър Л. Димитров]

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On 23:51 Tue 17 Jul, Thufir wrote:
>  Oh.  Why was the grub documentation not understandable like that?
>  maybe I misread it.  thanks for explaining!

I guess you missed it. `info grub' says (*Note chainloading)

---8<---8<----

4.1.2 Load another boot loader to boot unsupported operating systems
--------------------------------------------------------------------

If you want to boot an unsupported operating system (e.g. Windows 95),
chain-load a boot loader for the operating system. Normally, the boot
loader is embedded in the "boot sector" of the partition on which the
operating system is installed.

  1. Set GRUB's root device to the partition by the command
     `rootnoverify' (*note rootnoverify::):

          grub> rootnoverify (hd0,0)

  2. Set the "active" flag in the partition using the command
     `makeactive'(1) (*note Chain-loading-Footnote-1::) (*note
     makeactive::):

          grub> makeactive

  3. Load the boot loader with the command `chainloader' (*note
     chainloader::):

          grub> chainloader +1

     `+1' indicates that GRUB should read one sector from the start of
     the partition. The complete description about this syntax can be
     found in *Note Block list syntax::.

  4. Run the command `boot' (*note boot::).

   However, DOS and Windows have some deficiencies, so you might have to
use more complicated instructions. *Note DOS/Windows::, for more
information.

---8<---8<----

Note that it's usually better to refer to the info command for more
serious documentation about GNU tools in general. RMS and his guys don't 
exactly seem to like manpages that much that's what they have info for. 
They have their point, but that's another flame war ;-)


Regards,
	Aleks

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Re: [gentoo-user] Re: grub chainloader

[Stroller]

On 18 Jul 2007, at 13:35, Etaoin Shrdlu wrote:
> ...
> You can get everything at once and in the same place using the online
> docs:
>
> http://www.gnu.org/software/grub/manual/grub.html

This manual is very excellent.

I believe you can also get it in PDF format - I printed it out over 3  
years ago and still occasionally refer to it. How I miss my former  
employers' printer which would fold & stable paper to give A4 & A5  
booklets.

The GRUB manual is as good as lots of books you'd pay $$$ for.

>> And they are also written with the assumption that the reader
>> understands the confines a boot loader has to work in.

I don't know. I think the overview is pretty clear <http:// 
www.gnu.org/software/grub/manual/grub.html#Overview>, and leads into  
the remainder of the documentation quite well.

Stroller.
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Re: [gentoo-user] Re: grub chainloader

[Alan McKinnon]

On Wednesday 18 July 2007, Stroller wrote:
> On 18 Jul 2007, at 13:35, Etaoin Shrdlu wrote:
> > ...
> > You can get everything at once and in the same place using the
> > online docs:
> >
> > http://www.gnu.org/software/grub/manual/grub.html
>
> This manual is very excellent.
>
> I believe you can also get it in PDF format - I printed it out over 3
> years ago and still occasionally refer to it. How I miss my former
> employers' printer which would fold & stable paper to give A4 & A5
> booklets.
>
> The GRUB manual is as good as lots of books you'd pay $$$ for.

Yes, it is good documentation, in that everything is there - complete 
docs are a rare thing these days. But few people that I've come across 
thought to check the info pages and get it. 

> >> And they are also written with the assumption that the reader
> >> understands the confines a boot loader has to work in.
>
> I don't know. I think the overview is pretty clear <http://
> www.gnu.org/software/grub/manual/grub.html#Overview>, and leads into
> the remainder of the documentation quite well.

Well there's at least two people who know how boot loaders work. But 
it's not an easy concept to grasp for the average person. I get a feel 
that you are not an average person so your impressions are not valid 
for them. The big stumbling block is getting people to grasp that grub 
is not an OS, it's not a linux app as linux is not in memory yet. And 
yet, it can still read files and dirs that linux put there, and it's 
config file read at run time is a linux file. It's enough to make the 
average person's head spin (and does) - it can easily take two hours 
for me to get a class full of reasonably bright Windows techies to 
grasp why you use
kernel   (hd0,0)/vmlinuz-<version> <options>
with a separate boot partition, and
kernel   (hd0,0)/boot/vmlinuz-<version> <options>
when /boot is not a separate partition.

Then there's the bit about grub being able to load linux and 
Multiboot-compliant kernels natively, but Windows and others must be 
chainloaded...

None of this means that the grub docs are poor - it's just that 
bootloaders are tricky beasts to grasp and the docs are correspondingly 
hard to write so that Joe Average User gets it all first time through

-- 
Optimists say the glass is half full,
Pessimists say the glass is half empty,
Developers say wtf is the glass twice as big as it needs to be?

Alan McKinnon
alan at linuxholdings dot co dot za
+27 82, double three seven, one nine three five
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Re: [gentoo-user] Re: grub chainloader

[Neil Bothwick]

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On Wed, 18 Jul 2007 07:53:45 +0100, Mick wrote:

> If you have some reason not to mix one OS', or distro's boot files,
> kernels, etc with another, plus if you want to try a different version
> of grub then you can install grub separately in the new OS partition
> (instead of the MBR) and chainload this from your primary grub
> installation.  Should you wish to remove the new OS at a later date,
> you will not need to rummage through the primary OS' /boot to clean out
> redundant kernel images and what not.

You don't need to mix files to have more than one distro boot from the
same GRUB menu, just set the root() parameter accordingly for each distro.


-- 
Neil Bothwick

I am NOT Paranoid! And why are you always watching me??

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Re: [gentoo-user] Re: grub chainloader

[Stroller]

On 18 Jul 2007, at 16:00, Alan McKinnon wrote:
>> ...
>> I don't know. I think the overview is pretty clear <http://
>> www.gnu.org/software/grub/manual/grub.html#Overview>, and leads into
>> the remainder of the documentation quite well.
>
> ... The big stumbling block is getting people to grasp that grub
> is not an OS, it's not a linux app as linux is not in memory yet. And
> yet, it can still read files and dirs that linux put there, and it's
> config file read at run time is a linux file.

Um... surely the config file (um... grub.conf, right?) is _just_ a file.

It's not a Linux file, it's not a GRUB file, it's just a text file,  
which can be edited by any operating system that can write to the  
partition.

I have in the past considered putting grub.conf on a FAT32 partition  
- I'm not 101% sure that'd work but I've never tried because I never  
actually saw the usefulness.

> It's enough to make the
> average person's head spin (and does) - it can easily take two hours
> for me to get a class full of reasonably bright Windows techies to
> grasp ...

You clearly have more experience than I do with teaching novices  
about Linux.

You might ask them to consider - as a teaching aid - the Windows XP  
boot.ini file (I believe this is retired in Vista).

Boot.ini can be edited in Windows' Notepad in much the same way  
grub.conf can be edited with vi or nano. Very few Windows users will  
have any experience of doing more than removing an extra line (where  
the system was dual-booting to a previous installation of Millennium  
Edition, for instance) or reducing the countdown time before  
automatically booting the default entry, but if your students are  
bright then they will be aware of the boot.ini and will have done  
that much.

Stroller.
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Re: [gentoo-user] Re: grub chainloader

[Neil Bothwick]

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On Wed, 18 Jul 2007 17:06:57 +0100, Stroller wrote:

> I have in the past considered putting grub.conf on a FAT32 partition  
> - I'm not 101% sure that'd work but I've never tried because I never  
> actually saw the usefulness.

It will work, provided you call the file menu.lst, because the GRUB FAT
driver can only handle 8.3 filenames. The same applies when using GRUB on
a CD, it can't read grub.conf because it's not an ISO 9660 Level 1 name,
but it works fine with menu.lst.

So, in a way, grub.conf is a Linux file, because it needs to be on a
Linux filesystem for GRUB to read it :-/


-- 
Neil Bothwick

What Aussies lack in Humour they make up for in Beer!

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Re: [gentoo-user] Re: grub chainloader

[Thufir]

On 7/18/07, Александър Л. Димитров <aleks_d@gmx.de> wrote:
> On 23:51 Tue 17 Jul, Thufir wrote:
> >  Oh.  Why was the grub documentation not understandable like that?
> >  maybe I misread it.  thanks for explaining!
>
> I guess you missed it. `info grub' says (*Note chainloading)
>
> ---8<---8<----
>
> 4.1.2 Load another boot loader to boot unsupported operating systems
> --------------------------------------------------------------------
>
> If you want to boot an unsupported operating system
[...]

I was going by:

"13.3.4 chainloader
— Command: chainloader [--force] file

    Load file as a chain-loader. Like any other file loaded by the
filesystem code, it can use the blocklist notation to grab the first
sector of the current partition with `+1'. If you specify the option
--force, then load file forcibly, whether it has a correct signature
or not. This is required when you want to load a defective boot
loader, such as SCO UnixWare 7.1 (see SCO UnixWare). "
<http://www.gnu.org/software/grub/manual/grub.html#chainloader>

which is far less informative from my POV than the info message you
quoted.  I did refer to the manual, just the wrong one, apparently :)


-Thufir

Re: [gentoo-user] Re: grub chainloader

[Iain Buchanan]

On Wed, 2007-07-18 at 15:30 +0200, Александър Л. Димитров wrote:
> On 23:51 Tue 17 Jul, Thufir wrote:
> >  Oh.  Why was the grub documentation not understandable like that?
> >  maybe I misread it.  thanks for explaining!
> 
> I guess you missed it. `info grub' says (*Note chainloading)

[snip]

> Note that it's usually better to refer to the info command for more
> serious documentation about GNU tools in general. RMS and his guys don't 
> exactly seem to like manpages that much that's what they have info for. 
> They have their point, but that's another flame war ;-)

I'm happy to leave the info vs man flamewar for someone else, but what I
_don't_ like is when you have both man and info, and one of them is very
deficient (in grub's case, man).  The description is different, less
informative, and quite misleading.  Instead, is should say either
nothing but "refer to info pages"; or it should be the same as the info
pages...

would anyone agree?
-- 
Iain Buchanan <iaindb at netspace dot net dot au>

The trouble was that he was talking in philosophy, but they were
listening in gibberish.
        -- (Terry Pratchett, Small Gods)

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Re: [gentoo-user] Re: grub chainloader

[Iain Buchanan]

On Wed, 2007-07-18 at 17:00 +0200, Alan McKinnon wrote:
[snip]
>  I get a feel 
> that you are not an average person so your impressions are not valid 
> for them.

hahaha!!  If you know who this mythical average person is, let me know
so we can pay her $$$ to test all of our software!!

;)
-- 
Iain Buchanan <iaindb at netspace dot net dot au>

revolutionary, adj.:
	Repackaged.

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Re: [gentoo-user] Re: grub chainloader

[Thufir]

On 7/19/07, Iain Buchanan <iaindb@netspace.net.au> wrote:
[...]
> > Note that it's usually better to refer to the info command for more
> > serious documentation about GNU tools in general. RMS and his guys don't
> > exactly seem to like manpages that much that's what they have info for.
> > They have their point, but that's another flame war ;-)
>
> I'm happy to leave the info vs man flamewar for someone else,
[...]

A curious state of affairs.


-Thufir, who doesn't mind a good flamewar from time to time, with discretion
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Re: [gentoo-user] Re: grub chainloader

[Alan McKinnon]

On Wednesday 18 July 2007, Stroller wrote:
> > It's enough to make the
> > average person's head spin (and does) - it can easily take two
> > hours for me to get a class full of reasonably bright Windows
> > techies to grasp ...
>
> You clearly have more experience than I do with teaching novices  
> about Linux.
>
> You might ask them to consider - as a teaching aid - the Windows XP  
> boot.ini file (I believe this is retired in Vista).

Lucky it's something we don't run into too often :-)

I eventually figured out that how boot loading works is something most 
techies don't get into all that often. They understand all the various 
bits in isolation but when these bits are used together by grub 
it's ... different ... to normal use of the OS. Much the same as living 
in Europe and driving on the left, then going to the US and trying to 
drive on the right. For a few days your driving style is all fingers 
and thumbs but it settles down after some practice

alan

-- 
Optimists say the glass is half full,
Pessimists say the glass is half empty,
Developers say wtf is the glass twice as big as it needs to be?

Alan McKinnon
alan at linuxholdings dot co dot za
+27 82, double three seven, one nine three five
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Re: [gentoo-user] Re: grub chainloader

[Hans-Werner Hilse]

Hi,

On Thu, 19 Jul 2007 09:55:58 +0930 Iain Buchanan
<iaindb@netspace.net.au> wrote:

> I'm happy to leave the info vs man flamewar for someone else, but
> what I _don't_ like is when you have both man and info, and one of
> them is very deficient (in grub's case, man).  The description is
> different, less informative, and quite misleading.  Instead, is
> should say either nothing but "refer to info pages"; or it should be
> the same as the info pages...

Yeah, like a short synopsis and then a clear reference, let's say along
the lines of
----snip----
The full documentation for grub is maintained as a Texinfo manual.
If the info and grub programs are properly installed at your site,
the command

              info grub

should give you access to the complete manual.
----snip----

But looking at grub(8), it seems someone was faster. SCNR.

-hwh
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Re: [gentoo-user] Re: grub chainloader

[Iain Buchanan]

On Thu, 2007-07-19 at 13:36 +0200, Hans-Werner Hilse wrote:
> Hi,
> 
> On Thu, 19 Jul 2007 09:55:58 +0930 Iain Buchanan
> <iaindb@netspace.net.au> wrote:
> 
> > I'm happy to leave the info vs man flamewar for someone else, but
> > what I _don't_ like is when you have both man and info, and one of
> > them is very deficient (in grub's case, man).  The description is
> > different, less informative, and quite misleading.  Instead, is
> > should say either nothing but "refer to info pages"; or it should be
> > the same as the info pages...
> 
> Yeah, like a short synopsis and then a clear reference, let's say along
> the lines of
> ----snip----
[snip]

> But looking at grub(8), it seems someone was faster. SCNR.

OK, I'm an idiot.  I blabbed off at `man grub` without actually looking
at it... I thought it said something along the lines of the online grub
manual quoted by the OP... 

back to my hole.
-- 
Iain Buchanan <iaindb at netspace dot net dot au>

You know, Moe, my mom once said something that really stuck with me.  She
said, `Homer, you're a big disappointment,' and, God bless her soul, she
was really onto something.

		-- Homer Simpson
		   There's No Disgrace Like Home

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