[CentOS] Transferring system to new drive

Bill Campbell centos at celestial.com
Tue Sep 14 13:20:17 EDT 2010


On Tue, Sep 14, 2010, Timothy Murphy wrote:
>
>Is there a document with instructions for this?
>I've had smartd warnings that a hard disk in my server is sick,
>so I am installing a new drive (in addition to the old).
>
>I was thinking of copying the old root partition with
>	sudo cp -a -P /* /mnt/hd
>(after mounting the prospective new root partition).
>Then I'd have to modify the new /etc/fstab .
>
>Is that a sensible approach?

IHMO, the most sensible approach is to do a fresh install on a
new HD.  After the install is complete, install and mount the old
HD read-only to allow you to copy things over.

I just went through this process about 10 days ago when a fan
went Tango Uniform on our mail e-mail/file server which had been
up 1,390 days before the crash.  The old system had two
partitions, one for ``/'', the other on ``/home'' making it easy
to copy the old ``/home'' to the new one using any of a number of
tools.  I prefer ``cd /oldhome; find . | cpio -pdum /home'' as it
takes care of everything (of course it's important to add the
appropriate users and groups before doing this).

Using ``rsync'' would also work, but given that the initial copy
is not likely to have anything to update, I prefer ``cpio''.

Things get a bit more complicated when the old and new systems
are different distributions as user/group ids may differ.  In my
recent case, the old machine was running SuSE Linux Enterprise 10
while the new one is CentOS 5.current.  This required a bit of
``chown -R username: ~username'' work after the ``/home'' copy to
get things the way CentOS prefers.

In this case transferring user accounts was complicated a bit as
SuSE used different encryption in the ``/etc/shadow'' file so
simply copying the relevant part of the files was not sufficient,
but the passwords had to be reset so CentOS recognized them.

In our case, we didn't have to worry about things that were
installed under /usr/bin as we use the OpenPKG portable package
management system for pretty much everything including vendor
systems like openssh and postfix, and they are installed under
the ``/home'' file system.

Installing non-distribution software under /usr/local with that
either in its own file system or symlinked to a non-root file system
avoids having to sort out what belongs to the distribution, and
what has been added from other sources.  With most open source
software this simply requires using a simple option when building
``./configure --prefix=/usr/local ...''

This was standard practice with open source software long before
Linux came around, and is probably my main gripe with Linux
standards (the other is changing APIs without considering how
the change breaks installed systems).

Bill
-- 
INTERNET:   bill at celestial.com  Bill Campbell; Celestial Software LLC
URL: http://www.celestial.com/  PO Box 820; 6641 E. Mercer Way
Voice:          (206) 236-1676  Mercer Island, WA 98040-0820
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