Best practice for multiple version/OS boot?

[Adam Williamson]

On Mon, 2013-11-25 at 06:33 +0000, Tim Landscheidt wrote:

> More contested seems to be the multi-boot setup.
> https://bugzilla.redhat.com/show_bug.cgi?id=872826 has a
> myriad of opinions on how it should be set up;
> http://fedoraproject.org/wiki/User:Jlaska/Multiple_OS_Bootloader_Guide
> suggests "chainloader", and
> http://www.gnu.org/software/grub/manual/html_node/Multi_002dboot-manual-config.html
> recommends "configfile".  Of course there is also GRUB's OS
> prober.
> 
> So what are Fedora developers /actually/ using?  Creating a

I have noticed a fairly strong correlation here: the more you know about
how booting works, the more strongly you are inclined to avoid multiboot
as far as possible...

There really aren't any perfect options. The upstream advice of using
'configfile' as a sort of chainload-lite is probably the best approach
for grub2-booted OSes, overall. jlaska's page is outdated; upstream
grub2 explicitly discourages doing full chainloading. I'll slap a 'this
is obsolete' header on that page, I don't think James would mind. You'll
note, though, that the _design_ of both approaches is fairly similar:
have a 'master bootloader' not owned by any OS, let each OS own its own
boot configuration, and have the master bootloader read each OS's own
bootloader configuration when booting that OS. It's just that the old
'chainloading' method actually loaded each OS's bootloader, while the
'configfile' method has the master bootloader read in the config files
from the slaves rather than loading a whole bootloader that they
control.

Personally, I use VMs.

> separate GRUB partition and "chainloader"/"configfile"?
> Running OS prober in the "main" OS after each installation/
> kernel update?  Something else?  How often do the setups al-
> low one to shoot oneself in the foot, or are they (more or
> less) "foolproof"?

No, none of them are foolproof. I'd expect either the configfile or 'let
one OS be in charge and run mkconfig from that OS every time you update
any other OS' approach would mostly work most of the time. The
configfile approach is less of a pain and, because it involves less
manual work, less subject to snafus. If I really had to multiboot, I'd
probably go with the configfile approach.
-- 
Adam Williamson
Fedora QA Community Monkey
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