Installation of multiple Linux Instances

[Chris Snook]

kevin kempter wrote:
> Hi List;
> 
> I have a new dev server. As an independent consultant I want to maximize 
> it's use. Some of my clients use RedHat/CentOS 64 bit, others 
> Redhat/CentOS 32bit, some are even using Fedora and Debian.
> 
> Here's my thought:
> 
> I'd like to install each OS/version into it's own space on the disk.  
> I'm thinking all I have to do is install one OS (say CentOS 64bit) and 
> partition say 20% of the disk. Then once the install is done, boot into 
> the latest fedora disk and do the same, etc.
> 
> Is this correct ?
> 
> Later I want to add a disk array and allocate a RAID mount point that 
> can be mounted by any of the installed Linux'es when it's active.
> 
> Is this do-able ? Easily ?
> 
> 
> Thanks in advance...

If you can virtualize, you should, because it's a lot simpler, but if you can't, 
this is what I routinely do to solve this problem:

1)	Start with a grub-based distro first for ease of bootloader configuration. 
Make sure it's one you have a rescue disk for in case you screw something up and 
need to reinstall grub.

2)	Allocate a small /boot partition (200MB should be plenty) and put almost all 
of the rest of the disk in an LVM volume group, but leave a few GB free.

3)	Allocate your swap space and other shared filesystems (such as /home) in the 
LVM volume group.  All modern (2.6 kernel) distros will be able to use these. 
Allocate your root filesystem out of this volume group as well.  10 GB should be 
more than enough for any distro's root filesystem.

4)	When you install additional distros, allocate a small /boot partition out of 
the free space you left when partitioning, and put the rest in LVM.  Make sure 
to install the bootloader for the additional distros to the first sector of 
their boot partition, rather than the MBR, so it doesn't blow away the primary 
grub installation.  This is usually an option under "advanced bootloader 
options" or something like that.  If you accidentally blow away the grub 
installation, you should be able to reinstall grub with the rescue disk for the 
primary distro.

5)	Create a chainload entry in the grub.conf for the primary distro, pointing to 
the /boot partition for the new distro, like this:

title chainload RHEL5 (sda3)
	rootnoverify (hd0,2)
	chainloader +1

Now, at boot time, you'll get the list of kernels installed on the primary 
distro, and list of the other distros you can chainload.  If you choose one of 
the other distros, it will launch that distro's bootloader, and then boot it 
normally.

This is a little bit of a pain, but it works.  I recommend using virtualization 
when suitable, as it saves a lot of the hassle of bootloader configuration. 
Putting most of your disk in LVM will also allow you to allocate logical volumes 
to be virtual disks, which is MUCH faster than file-backed virtual disks, so 
this partitioning scheme works for both purposes.

Make sense?

-- Chris