how to integrate an old installation in Grub and startmenu

[Robert Heller]

At Mon, 13 Sep 2021 13:58:22 +0200 "Ubuntu user technical support,? not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:

> 
> On Mon, 13 Sept 2021 at 13:49, Robert Heller <heller at deepsoft.com> wrote:
> >
> > They are
> > especially bad if you have a "shared" /boot FS (which you really should have if
> > you are multibooting Linuxes)
> 
> I am sorry, but *what?!*
> 
> Sharing /boot between different distros?! That sounds _suicidal_.

It was necessary with Grub1 (and Lilo before that), which no clue about LVM
and even Grub2 has issues with some RAID modes and metadata versions. It was
also necessary on machines with multiple disks, various RAID, and other
interesting setups. It was actually commonplace since early days. I've never
had any problems, until I moved to Ubuntu 18 and the Grub2 config scripts
started doing silly things like trying to pair a CentOS 6 kernel
(2.6.something) with a Ubuntu 18 root file system... But that was easily fixed
by hacking the Grub config scripts and adding some new ones to understand
about CentOS 6 (and 7) kernels and root file systems. So long as the /boot FS
was large enough, kernel installers just installed kernels side-by-side. The
only issues would be updating grub.conf (Grub1) (and lilo.conf before that),
which could always be hand edited as needed.

> 
> BIOS_BOOT partition on UEFI/GPT, sure. But that is _not_ a /boot FS.
> 
> > and really bad when the "other" Linuxes are for
> > a completely different distro (eg RedHat / CentOS).
> 
> I think my personal record is 7 different distros on a single hard
> disk (alongside DOS *and* Windows). It's perfectly doable, but you do
> need to know what you're doing and plan ahead.
> 
> I have successfully multibooted Mint + Ubuntu + Fedora + Arch + SUSE
> on the same machine, for instance. Fedora and SUSE were both major
> pains, though.
> 
> > It also gets confused if
> > you are using LVM and have Linux VMs using LVM volumns for their disk space.
> 
> *Everything* gets confused -- and confusing -- if you use LVM, which
> is why I advise people not to.
> 
> Anyone who needs to ask for advice on things like multibooting should
> not be using it, IMHO. *I* need to ask for advice regularly and I've
> been doing this stuff for >30 years now.  I find LVM confusing,
> intimidating and a pain.
> 
> I completely accept that there are many many people more skilled than
> me who use it with aplomb. I am not an egomaniac.

LVM is *extreemly* handy when you want/need lots of file systems (eg 
partitions) that you need to create and/or resize without have to shutdown to 
single-user mode and reboot everytime.  It is also a great way to migrate the 
whole batch of file systems to a new physical "disk" --  add the new PV, then 
"condem" the old PV, and there you are.  With hot-swap disk bays, you don't 
even have to shutdown and reboot.  I also use LVM volumes for VMs -- I can use 
snapshots to back up the VMs and don't need to either stop or start the VMs.


> 
> But OTOH if it's on a server deployment, well, servers generally do
> not dual-boot and probably shouldn't. Keep the recovery system on
> another disk altogether. And these days you should probably be running
> it under a hypervisor anyway.
> 
> 

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