[PLUG] CentOS 7 iso too big to burn...

David Bridges dbridges at austin.rr.com
Fri Mar 31 22:29:19 UTC 2017


As others have stated upgrading CentOS/RedHat is not really an option
but the options below will allow you to use the ISO to do a fresh
install on the new disk.

On Thu, 2017-03-30 at 22:59 -0700, Michael Robinson wrote:
> The CentOS 7 iso is 7.8 gigs.  My DVD-R media tops out at about 
> half that.  The server I'm trying to upgrade would have to use
> an external DVD drive in order to upgrade from a DVD.
> 
> I am trying to upgrade from CentOS 6.8 to CentOS 7.3.  I want
> to install CentOS 7.3 on a newly installed and unused 500 gig SSD.
> So far, I have created a 10G ext2 partition at the beginning of the
> new SSD and I have copied the CentOS 7.3 iso's contents to it.  I 
> used a loop mount to mount the iso and then cp -av.  I am trying
> to figure out how to install from a local hard drive instead of 
> a DVD disk.
> 
> I have Grub 1 in CentOS 6.8, is there a way to trigger the installer
> from my existing Grub on the second SSD?  Can I seamlessly upgrade 
> the old CentOS 6.8 to use Grub 2 instead of Grub 1?

I would not copy anything to the new disc that you want to use.  You
can just place the ISO on your current installation and create an entry
to boot into the CentOS 7 installer using your current grub following
the instructions below.

Mount the ISO and copy vmlinuz and initrd.img to your current /boot
partition from the images/pxeboot directory of the ISO.

You can create and entry in /boot/grub/menu.lst that resembles the
information below but it adjusted according to your current
installation.  I would suggest that you not make this the first entry. 

title installer
	root (hd0,0)
	kernel /vmlinuz
inst.repo=hd:vda3:/CentOS-7-x86_64-DVD-1611.iso
	initrd
/initrd.img

The root line should be exactly the same as the other entries in the
file (assuming you put the vmlinuz and initrd.img files in /boot)

You will need to change vda3 to whatever partition the ISO is located
on and them modify that path to the ISO.  You will need to make sure
that you do not rename the ISO or this will not work without additional
parameters.

Reboot your computer and when you see the grub screen press space to
get a menu that shows you all boot options, select installer.

This will boot you into the installer so that you can install to your
new disk.  It will not modify your current bootloader, the install will
install grub2 on the disk you install to (make sure you install to the
correct disk).

Almost all computers will allow you to pick the disk you want to boot
by pressing some key in order to see a list of devices, if not you can
more than likely set it in the BIOS.  In order to be able to use the
new disk as the boot device.  Once you are in the new OS you can have
CentOS probe for your other installation and create an entry for it so
that you can boot it with the following command.

grub2-mkconifig -o /boot/grub2/grub.cfg

This still does not modify the boot sector on your original install. 
If you want to boot your original install (old grub) but also have the
option to boot into the new installation you can run the following
command.

grub2-install /dev/sda (modifying sda to be the device your original
install was on)

These instructions will work but if not done correctly can trash your
system so proceed at your own risk.

--
David





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