--recheck option

--recheck option

[yannubuntu]

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Dear GRUB devs/helpers,

A) Which are the situations where the --recheck option of grub-install must
NOT be used? why grub-install wouldn't systematically probe a device map by
default?

B) Some people recommend to use "grub-install /dev/sdX && grub-install
--recheck /dev/sdX", do you think it is correct/useful?

Regards
Yann

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Re: --recheck option

[Jordan Uggla]

On Thu, Jul 5, 2012 at 5:19 AM, yannubuntu@gmail.com
<yannubuntu@gmail.com> wrote:
> Dear GRUB devs/helpers,
>
> A) Which are the situations where the --recheck option of grub-install must
> NOT be used? why grub-install wouldn't systematically probe a device map by
> default?

With grub 2.00, it does.
http://www.gnu.org/software/grub/manual/grub.html#Device-map .

>
> B) Some people recommend to use "grub-install /dev/sdX && grub-install
> --recheck /dev/sdX", do you think it is correct/useful?

As explained in the above documentation, grub utilities no longer need
a device.map file. Back when they did still need one, the first time
someone ran grub-install it would write a device.map (if one didn't
already exist). If that got out sync somehow then a later grub-install
might fail, and if that happened using the --recheck option (which
would write a new device.map, overwriting the old one) might allow the
installation to succeed.

Now, grub-install probes on the fly if no device.map exists, and never
creates a device.map file itself, and so "grub-install --recheck ..."
now actually simply deletes the device.map file, causing grub-install
to go back to the default state of probing on the fly.

Running grub-install twice is redundant, and adding the '--recheck' is
also usually not needed option at this point but won't hurt anything
(except in very specific situations like when you're passing an LVM
logical volume to a virtual machine as if it were a normal disk, in
which case you should know what you're doing and have a backup of your
device.map anyway).

So the advice is a little silly at this point, but not harmful.

-- 
Jordan Uggla (Jordan_U on irc.freenode.net)

Re: --recheck option

[yannubuntu]

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2012/7/5 Jordan Uggla <jordan.uggla@gmail.com>

> On Thu, Jul 5, 2012 at 5:19 AM, yannubuntu@gmail.com
> <yannubuntu@gmail.com> wrote:
> > Dear GRUB devs/helpers,
> >
> > A) Which are the situations where the --recheck option of grub-install
> must
> > NOT be used? why grub-install wouldn't systematically probe a device map
> by
> > default?
>
> With grub 2.00, it does.
> http://www.gnu.org/software/grub/manual/grub.html#Device-map .
>
> >
> > B) Some people recommend to use "grub-install /dev/sdX && grub-install
> > --recheck /dev/sdX", do you think it is correct/useful?
>
> As explained in the above documentation, grub utilities no longer need
> a device.map file. Back when they did still need one, the first time
> someone ran grub-install it would write a device.map (if one didn't
> already exist). If that got out sync somehow then a later grub-install
> might fail, and if that happened using the --recheck option (which
> would write a new device.map, overwriting the old one) might allow the
> installation to succeed.
>
> Now, grub-install probes on the fly if no device.map exists, and never
> creates a device.map file itself, and so "grub-install --recheck ..."
> now actually simply deletes the device.map file, causing grub-install
> to go back to the default state of probing on the fly.
>
> Running grub-install twice is redundant, and adding the '--recheck' is
> also usually not needed option at this point but won't hurt anything
> (except in very specific situations like when you're passing an LVM
> logical volume to a virtual machine as if it were a normal disk, in
> which case you should know what you're doing and have a backup of your
> device.map anyway).
>
> So the advice is a little silly at this point, but not harmful.
>
> --
> Jordan Uggla (Jordan_U on irc.freenode.net)
>


If I understood well,
- we should recommend using --recheck for 1.98<=GRUB<2.00. Advanced users
using device.map will know if they don't need --recheck.
- using --recheck or not makes no difference for GRUB>=2.00

Am I correct?

(is the --recheck option kept in 2.00+ for retro-compatibility?)

Thanks a lot
Yann

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Re: --recheck option

[Vincent Pelletier]

Le jeudi 05 juillet 2012 14:19:54, yannubuntu@gmail.com a écrit :
> A) Which are the situations where the --recheck option of grub-install must
> NOT be used?

In my experience (grub legacy, linux boot with /dev/hd* device names, years 
ago), I had to play with device map to be able to reorder boot device priority 
(or plug HDDs in a different PATA layout, I don't remember precisely).
I could edit the map to fit the intended layout change, grub (without
--recheck) just followed, and machine could boot just fine.

Nowadays I don't have to care about this, thanks to UUIDs everywhere instead 
of dev paths.

-- 
Vincent Pelletier