On 10/26/2014 09:24 AM, Timothy Murphy wrote:
Ted Miller wrote:
I would like to upgrade a CentOS-6.5 home server
to CentOS-7 on a new partition.
What is the simplest way to achieve this?
1. It requires a custom disk layout, but is not particularly hard.
2. AFAIK, you can share your SWAP partition between the two installations.
3. Centos 7 uses grub2 as its boot loader. It is significantly different
from "legacy grub" used in Centos 6 and before.
a. It uses a configuration file that is auto-generated, and not
supposed
to be edited.
b. It is capable of finding other installations (including legacy grub
and windows), and creating links to them.
c. 'b' only seems to work IF the other boot partitions are mounted
somewhere in your file tree. What I have done is mount the other
partitions (the /boot partition, if it is on a separate partition,
otherwise /) under /mnt (e.g. /mnt/C6) when you are doing your custom disk
layout. As long as they are mounted somewhere in the file system, grub2
seems to find them OK, and add them to your boot menu. It is apparently
incapable of looking on unmounted partitions and finding Operating Systems
lurking there.
d. grub2 is (theoretically) capable of booting off of LVM (and I have
done so successfully), BUT that capability is disabled and unsupported in
RHEL/Centos 7. You still have to put /boot on a non-LVM partition.
Thanks very much for your response.
A couple of comments:
3. Curiously, I see I already have a file /boot/grub2/grub.cfg
on my CentOS-6.5 system,
though /etc/grub.conf points to /boot/grub/grub.conf .
Did I create the grub2 file while experimenting with the system,
or is it provided by CentOS-6.5 to simplify upgrading?
Never had that happen, so can't comment.
3b. When I upgraded another server to CentOS-7
it did not seem to find the old CentOS-6.5,
although it found a Windows system OK.
However, I was using the old /boot partition for the new system.
Sounds like it was looking for /boot/grub, and you over-wrote that when you
installed the new system in the old /boot partition.
I have gotten in the habit of either creating or leaving unused some space
on any disk that might be used as a boot disk, rather than committing all
the space to LVM. That way I have something to work with if I need "yet
another" boot partition.
I'll try mounting the old boot as /mnt/C6 in the custom setup
during the new installation, as you suggest.
I shall not give a separate partition for the new /boot -
hopefully I shall be able to move /boot to a new partition later.
I had thought, as an alternative method, of cloning the old system
to a new partition, and trying the new CentOSUpgradeTool on this.
(I'm running a CentOS-6 KDE system, and note that the documentation
for the new tool says it will probably not work with KDE or Gnome -
which I would have thought would rule out 95% of systems -
but it wouldn't matter too much if I still had the old system.)
I have not tried an upgrade, but it sounds like they put the work into
making server upgrades easier, but did not (or could not) make it as easy
for desktop installations. Most people paying license fees are covering
servers.
Ted Miller
Elkhart, IN, USA
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