[Sussex] Linux dual boot

[Alan Pope]

On 31/08/05, Gavin Stevens <starshine at gavmusic.uklinux.net> wrote:
> A while ago, I set up a Windows/Ubuntu dual boot on my partner's PC.
> This was fairly easy to do & worked first time.
> 

Most modern Linux distros can cope with being installed side-by-side
with something else, which is good news for dual-booters.

> On my own second PC, I decided to try a dual boot of Debian Sarge &
> CentOS 4.1. Perhaps naively, I thought it would be relatively easy to
> achieve. This has not been the case: I made a partition for CentOS when
> I installed Sarge. The CentOS partition had a mount point of "/centos",
> but CentOS was not impressed with this when I came to install it. It
> said it needed a "/" directory in order to know where to install itself.
> 

Right, that's where you went wrong. A disk can be carved up into
partitions, up to 4 primary ones (hda1 through hda4 for example on the
primary master IDE disk) and some extended ones (usually starting at
hda5 for primary master IDE disk). What you put in them is up to you,
but if you want multiple Linux distros that's going to be a minimum
requirement - multiple partitions.

Once the disk is carved up (not forgetting some space set aside for
swap) using whatever disk partitioning tool you choose - cfdisk,
fdisk, parted, disk druid or whatever, you then need to choose what
mount points are going to go *in* those partitions. For the absolutely
simplest of installations of Linux you can get away with "/" - the
root mount point being one partition - say /dev/hda1 for example, and
the swap being maybe /dev/hda5.

You could get more fancy and have separate paritions setup for mount
points such as one for /home, one for /var, another for /usr and a
further one for /boot, all in addition to the one you already created
for /. You don't have to do this, and for the beginner it can be
easier to just have one partition for / and be done with it. I'm
guessing this install you're doing wont be a long term solution, but
will be a play thing, so you could install multiple times using
different partitioning setups.

The crucial thing to note is that one linux distro will need a /, and
so will another that you install. So  you could for example create
/dev/hda1 of 2GB, and /dev/hda2 of 2GB also. One could be / for
debian, the other could be / for centos. Two separate partitions into
which the different distros are installed, keeping all their files
separate. The only bit of disk they'd share would be the swap and the
boot loader.

> Presently, I have the partitions set up like this:
> 
> /dev/hda1       /       primary, bootable
> /dev/hda3       /1      primary
> [/dev/hda2              extended]
> /dev/hda5       /home
> /dev/hda6       swap

Ok, really the hda3 and hda1 should both be /, there's no such thing
as /1 really. This is a common mistake made by Windows veterans who
are used to having to use folders to organise stuff. Now there's the
extra level of partitions above that, it makes things a bit more
complicated, but not too much.

> /dev/hda3 has been renamed "/1" after having to re-install Debian (at
> which point, I deliberately wiped the CentOS install, leaving that
> partition ready to have another go).
> 

Hmm. I'm not sure I follow, but I am sure that lots of the confusion
lies with the /1 stuff. It just plain shouldn't be there. All the
linux installs on this box - however many you have, should all have a
/ - wherever that partition is.

> Before I get into questions about GRUB (actually, I'm not confused about
> GRUB), I need to establish the correct way to install the two distros,
> plus any alterations to the partitions that could be helpful (if it is
> possible to do this on one HDD).
> 

If you're starting with a blank disk then the first distro you install
will guide you through partitioning, just make sure you leave some
empty space - or indeed create an extra partition for - the next
install you'll do later of the "other" distro. When you come to
install the next distro make sure you tell it to install in the
"other" partition for its /.

You may have issues with GRUB not "seeing" the first distro install
when you install the second one. It's not really "normal" to have
multiple installs of linux on a box, although supported, and it will
work just fine, it's a bit "odd" IMO. I know that last sentence is
going to get lots of "I dual boot multiple distros, what are you
talking about?" but I shall ignore them.

> I only have the one HDD in the second PC, but if a second drive is
> adviseable, then I can easily get one from work.
> 

No, should't be needed, so long as the one you have is big enough for
a) a / part for one distro, b) a swap part for both distros to share,
c) a / part for the second distro. A few gig should be enough for a
minimal install of two distros, any bigger than that and you can have
fun with X/Gnome/KDE/etc too if the machine is up to it and you're
interested in it.

> Finally, just to re-iterate that all of the above is taking place on my
> second PC, which I built especially for learning & experimenting. So I
> can re-format, re-install etc. as necessary without any fear of data
> loss.
> 

Personally, given what you've said, I'd start again. Plan out the
partitioning schema on paper first, as I outlined above.

> Some may ask why I am bothering to attempt this at all: It is purely for
> learning purposes. It does have a possible link in to my planned
> "non-techie" presentation at a moot, but I have a strong desire right
> now to get my hands dirty with Linux & know a lot more.
> 

Hey, there's nothing wrong with trying stuff out, it's the absolute
best way to learn.

> I have already learned one thing: It is easier to set up a Windows/Linux
> dual boot than it is to do a Linux/Linux dual boot.
> 

I'll not comment on that for fear of casting aspertions on your
partitioning schema. :D

Hope that helps,

Cheers,
Al.