[CentOS] Question on upgrading hardware

[Dave K]

On Thu, Jan 22, 2009 at 8:27 PM, nate <centos at linuxpowered.net> wrote:
> Bob Hoffman wrote:
>> For centos 5.x

>> 2- If I built another system, slightly different motherboard but most of the
>> rest the same as far as hardware, would taking a drive from the old system
>> and adding it to the new system work correctly and recognize what it needs?
>
> If the disk controller is the same you should be fine. If it is not
> the same you may want to adjust your /etc/modprobe.conf and rebuild
> your initrd prior to making the change to ensure the system boots.

I haven't tried this with CentOS 5.x, but have with other
distros/releases.  One thing that often happens is that the network
configuration will need to be re-run.  When kudzu (is that still in
5.x?  My 5.x system is down at the moment :( ) sees that the network
interface has changed, it deletes the config for the old one, than
asks you to configure the new one.  So be prepared to re-enter all the
interface details. Or save the existing config, and make the necessary
edits in single-user mode.

If you have a custom X setup, you should move it aside and let the
defaults take over again.

To make the transition easier, and to allow step-by-step testing, it
might be a good idea to set the initial run level to 1 before removing
the disk from the old system, make sure everything that you see looks
okay in single-user, jump to run-level 3, again check everything, then
try for run-level 5 (if that's where you're headed).  Leaving the
initial run-level at 1 or 3 is particularly helpful when you aren't
sure if the X config is working, as a bad X config can be a real pain
to work around (yes, you should be able to get to a virtual console
and so on, but SHOULD is the operative word).

In general, the more customizations you've made, the greater the
chance of problems.  One area of concern is the grub settings.  The
more specific they are to the hardware, the greater the chance of
failure.

Having a working live-cd (or usb key or whatever) that runs on the new
hardware could also be a life-saver.

If you have problems, there are some things I've done in the past to
recover failed systems:

1) Do an install to a "new" disk in the new hardware, and make note of
the various configuration settings.  Make the "old" drive the second
disk, and transfer those settings you need (ALWAYS KEEPING BACKUP
COPIES, of course).

2) If you mangle things to the point where things look unrecoverable,
don't despair.  You can try doing an "UPGRADE" installation of the
same distro/release using the old disk, that will often fix grub and
kernel configuration issues.  But that will also downgrade a lot of
packages back to the original release versions, so a full update will
be required afterwards.

By the way, you have made backups of all your
important/critical/valuable data, right? (Backups of /etc and /boot
can also be helpful if things start "going wrong".)

-- 
Dave K
Unix Systems & Network Administrator
Mount Laurel NJ