On Sun, Jun 10, 2018 at 12:36:02PM +0100, Simon Hobson wrote:

> I think you may be confused about what this section is doing. You are
> telling the installer a) what to do with a disk & it's partitions (eg,
> should it format a partition), and b) where they should be mounted.
> So for your partitions on sda, you tell it NOT to format them and not
> to mount them anywhere - I certainly recall those being options in the
> Debian installer, you may need to go into expert mode. Alternatively,
> tell the installer NOT to format them and set a different mount point
> (eg /jessie, /jessie/boot, ...) When you set a mount point, it's
> telling the installer two things : where to mount the filesystem
> during the install, and what to put in the installed system's
> fstab. If you tell it to do nothing with the partitions/filesystems on
> sda, then they will simply be left alone - but watch put for grub
> install later on, you don't want to damage the grub that's already
> installed. So don't format the partitions on sda, don't mount them
> anywhere, and you'll end up with a new install on sdc that just
> ignores the system already on sda - but as mentioned, be careful when
> it comes to grub install time. Then (I assume through the system
> BIOS) you'll be able to boot using the old system & it's grub on sda,
> or the new system & it's grub on sdc.

Don't underestimate my ability to get confused, especially when a
practice I've followed for years no longer works. It may be the
difficulty arises now because two of the machine's disks are for ascii
(one rc and the other stable), and jessie is on sdb. Does the conflict
over use of \ only happen if operating system versions happen to be the
same? If so, I wonder if an expert installer could be warned of this and
what to do about it. For example, the error message that pops up could
be more informative.

In the partitioner, when I go to edit a partition, one option is to "use
as:" If I specify to use as ext4, then the additional
settings become available of whether to format the partition and set its
mount point. If instead I chose "do not use", I no longer have the
option to format and define a mount point.

That is as you say, but your comment about watching out for GRUB later
on in the installation worries me. You warn me that I should not allow
grub to "damage" (confuse?) the grub on sda, but the installer asks a
question that I do not find to be clear. When installing GRUB and after
the installer discovers what operating systems happen to be accessible
for the installation, it tells me it is safe to install GRUB in the mbr
of the first drive, which in my case is sda. My intent is to leave GRUB
as it is on sda and to install it instead on sdc. However, it then asks
whether to install it in the mbr. To which drive does this refer? Is it
asking if I want to install GRUB in the mbr of the first drive, sda, or
is it asking simply whether to install GRUB the mbr on whatever drive I
next install GRUB?

Haines