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Re: Dual Boot

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Le 27/11/2016 à 21:02, Jan Bakuwel a écrit :
>
> On 26/11/16 11:01, Pascal Hambourg wrote:
>>
>> When embedding is not possible, the core image is stored as a regular
>> file in /boot/grub. Then /boot/grub must be on the same drive as the
>> boot image. However blocklists are not reliable with files, because
>> the filesystem may move blocks containing a file around.
>
> I find it extremely useful (to the point where it once literally saved
> me from disaster which is a story beyond the context of this thread) to
> have multiple OS-es installed on any machine. I've been doing that for
> years and even with grub it has - so far - always worked fine. But I
> hear you that that's not a guarantee, and thus I started using extlinux.

I think that I experienced that problem once (but not sure), and needed 
to reinstall GRUB. To be honest, the chances that the blocs containing 
the core image may be moved around are very thin if you have a separate 
ext2 /boot partition, which is rarely modified.

> Which brings me to the following question: what is the recommended way
> to boot multiple OSes with grub, for example with a partition layout as
> below. Or is there simply no sane way to do this with grub?

I would not pretend to know "the recommended way".
However I would recommend a few layouts for some configurations.

If EFI boot is an option, then install all systems for EFI boot (for 
Windows this implies a GPT partition table on the boot disk). This way 
all bootloaders can be installed in separate directories in the EFI 
system partition without overwriting one another. You can define one of 
them as the primary boot loader with higher boot priority in the EFI 
boot list.

For BIOS boot, without Windows I would recommend to install a primary 
GRUB in the MBR with embedding. Install secondary GRUBs in partitions 
boot records, without embedding. Then you have several options :

- add all entries for Windows and other Linux system kernels in the main 
GRUB menu, which can be done automatically with os-prober called by 
update-grub. The drawback is that the main boot menu must be updated 
everytime a secondary boot loader is updated.

- add entries to chainload the secondary boot loaders in the main GRUB 
menu, so that the main boot menu does not have to be updated when a 
secondary boot loader is updated. The "multiboot" command can be used to 
load a secondary GRUB core image file, so the embedding requirement does 
not apply here.

- include or load secondary GRUB config files in the main boot menu. 
This does not work well with different versions of GRUB, so I do not 
recommend it.

One must also decide whether to use the GRUB belonging to one of the 
Linux systems or an independent GRUB as the main boot loader. Of course 
there is less risk to damage an independent boot loader.

So my advice for a safe setup would be to :
- install the main GRUB in the MBR and its own partition for /boot/grub
- install each secondary GRUB in its OS partition
- chainload secondary GRUBs in the main GRUB's boot menu

Unfortunately with Windows the MBR is not a safe place because Windows 
overwrites the MBR at installation and sometimes when updating, so be 
prepared to restore a backup or reinstall GRUB. The boot record of the 
main GRUB's partition is a safer place, but it prevents embedding, so 
the risk of moving blocks comes back. However this partition should not 
be mounted and modified often, so the risk is low.

> /dev/sda1: boot/rescue system
>
> /dev/sda2: Windows 7
> /dev/sda3: Windows 10
>
> /dev/sda5: /boot - Linux system 1
> /dev/sda6: / - Linux system 1
> /dev/sda7: /var - Linux system 1
> /dev/sda8: /var/log - Linux system 1
>
> /dev/sda9: /boot - Linux system 2
> /dev/sda10: / - Linux system 2
> /dev/sda11: /var - Linux system 2
> /dev/sda12: /var/log - Linux system 2
>
> /dev/sda13: swap
> /dev/sda14: LVM

 From the missing /dev/sda4, I guess it is an extended partition and 
/dev/sda{5..14} are logical partitions in a DOS/MBR scheme. 10 logical 
partition is quite a lot. The linked list extended partition structure 
is quite fragile and rigid. A GPT partition table would be more robust, 
but it requires to reinstall reinstall Windows in EFI mode, and of 
course that the motherboard firmware is a UEFI. Otherwise, using LVM for 
most filesystems and swap is an option to reduce the number of partitions.

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Thread

Dual Boot Dan Norton <dnorton@mindspring.com> - 2016-11-25 16:50 +0100
  Re: Dual Boot Hans <hans.ullrich@loop.de> - 2016-11-25 17:00 +0100
    Re: Dual Boot Jan Bakuwel <jan.bakuwel@gmail.com> - 2016-11-25 19:40 +0100
      Re: Dual Boot Pascal Hambourg <pascal@plouf.fr.eu.org> - 2016-11-25 23:10 +0100
        Re: Dual Boot Jan Bakuwel <jan.bakuwel@gmail.com> - 2016-11-27 21:10 +0100
          Re: Dual Boot Pascal Hambourg <pascal@plouf.fr.eu.org> - 2016-11-28 00:50 +0100
            Re: Dual Boot Jan Bakuwel <jan.bakuwel@gmail.com> - 2016-11-28 05:30 +0100
  Re: Dual Boot Alexandre GRIVEAUX <agriveaux@deutnet.info> - 2016-11-25 17:10 +0100

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