[Gllug] Fdisk in a pure Linux environment

Alain Williams addw at phcomp.co.uk
Wed Nov 30 00:29:13 UTC 2011

On Wed, Nov 30, 2011 at 12:44:16PM +1300, David L Neil wrote:

> I am thinking of partitioning the new drive:
> - 100MB ext2 for /boot
> - 2GB for /swap (theory saying <= RAM size)
> - rest as ~100GB partitions which would be LVM-ed for both system and 
> data mount points, as needed, and over time.
> Reading some recent material indicates that my knowledge/memory and 
> history are being surpassed (although I'm not talking about UEFI). So 
> I'm pondering the following questions:
> Isn't the "Boot" star (as reported in Fdisk) now only a hang-over from 
> MS-Windows, in fact MS-DOS, and thus irrelevant to a pure-Linux machine?
> So can it be ignored totally, relying upon setting boot-drive priorities 
> in the BIOS?

> Can the entire drive be partitioned as a single Extended partition (no 
> Primary partition at all) and that sub-divided into Logical partitions 
> from there?

I think that the latest grub can understand /boot inside LVM, but I have not tried it.
So I still have a separate /boot as /dev/sda1 (or whatever).

> When the time comes (and all else being equal!), will CentOS 6 boot 
> happily (under BIOS direction) from such a HD set-up?

It will boot happily if the BIOS can be made to boot off the hard disk
and, when you do the install, you get GRUB installed in the MBR for the disk.

You can probably install under qemu - it might be slow if it really has to emulate
a lot - but it should work. This may/may_not be acceptable considering what else
the machine is doing. You give it the new hard disk and get it to lay it out as
you wish.

I would go with partitions:
a  100 MB /boot ext2 or ext3
b  the rest of the disk as LVM, how you partition depends on what you are doing
   but since it is LVM you can expand partitions as needed later on. For starters try:
   - 1GB RFS
   - 2GB Swap
   - 5GB /usr
   - 2GB /tmp
   - 2-4GB /var
   - ?? /home

Note that the Centos 6 installer needs a machine with at least 652MB of RAM,
so that will take much of the 2GB that I think you have. Once it is installed
you can run it under qemu again with a smaller amount of memory.

BEWARE: when do you do a real (non qemu) boot you may find that it will
not boot because the initrd created will be for the qemu environment and
so not match the real hardware. That is not an issue: boot off CD, chroot
into your new environment, run mkinitrd to overwrite the initrd in /boot
and you should be OK.

> Meantime as soon as I can physically install the HDD I'd like to employ 
> some of the disk space for data or work-space during the 
> archiving/spring-cleaning process preparatory to the migration/upgrade...

In which case you will need to have
sda1 - 100MB /boot - new system
sda2 - 20GB+ lvm for the new system
sda3 - rest lvm for you tidy up

Once you have switched to the new system you should be able to import the LVM
on sda3 and access it.

Alain Williams
Linux/GNU Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256  http://www.phcomp.co.uk/
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