Going from Centos 6 to Ubuntu Server

Mon Mar 26 23:45:26 MST 2012

Wow!

This is the first I've seen here that ANYONE is using a seperate /boot partition.

I've been using one since about 2.2 kernels.
I started out using 50Mb but, with Ubuntu and GRUB 2.0
it needs around 300Mb to 500Mb.  A Fedora 15 install didn't
complain using a little as 150Mb.  The minimum is for my
Windows "ntldr" which requires only 50Mb.

I've never needed LVMs or software raids for my desktop.
As I understand it, they are not involved during boot, but are
a requirement to access the newer GRUB config scripts in Ubuntu.
Use a live boot disc, as Stephen says, to be sure they are accessable.
Most of my (single-user) boxes have three to seven OSes to boot from.
All within a less than 100Gb hard drive.  I'm using Grub Legacy.

If your Centos server is a large system, you may rather try this on a
seperate hardware test machine, for safety.  I've seen trouble from the
Ubuntu GRUB scripts.  Specifically, their "os_prober" has problems
identifying other bootable kernels and systems when generating 
the new Ubuntu boot menu.

Another problem is that Ubuntu is capable of GPT or MBR hard drives.
MBR is the classic Master Boot Record.
GPT is newer, larger, and demands specific hardware abilities.
I've seen Win 7 using GPT, so caveat emptor.

  (-:  Chas.M.  :-)

Date: Wed, 21 Mar 2012 20:11:34 -0700
Subject: Re: Going from Centos 6 to Ubuntu Server
From: nadimhoque at gmail.com
To: plug-discuss at lists.plug.phoenix.az.us

Well with my setup I do have the boot partition separate from the LVM and the raid is pure software as far as I know. I was just asking if it was safe to do so. Unfortunately the boot partition is a bit on the smaller size at 100mb so I can easily fit around 2 kernels. I guess the other reason I am thinking to switch is because with Ubuntu, they have a predictable release schedule and with 12.04 LTS around the corner, I can get a server OS that is "stable" and up to date. I know I can compile from source all of the packages I have, like the the kernel and the software for the LAMP stack that I am also running. 

I also like the fact for the Ubuntu implementation of Samba; I can use the the system username and password instead of first creating a user on the system and again as a samba user. Other than that I do like Centos right now. Thanks for your help.

On Wed, Mar 21, 2012 at 7:21 PM, Michael Butash <michael at butash.net> wrote:

Should be able to - depends how you're partitioned.

I'm assuming your raid0 is done with mdadm and not fake-raid based.

As long as your boot partition (non-lvm) is large enough to support enough kernels, you should be able to install over the system lv's you don't want, and not touch the ones that you do.  Probably just create new lv's assuming you have the space for new root, usr, var, whatever you want.  I usually create home without a separate partition, leaving alone the existing home, and simply mount the /home lv after reinstall "just in case".

Note I've had some weirdness with ubuntu/mdadm depending what version mdadm metadata it was built with.  In 11.04 I had to build md's specifically to use 0.90 metadata to work fully (i.e. reboot without having to busybox assemble md manually), 11.10 and higher I had to build the raid specifically with the current version (default) to work.

I layered luks/lvm/ext4 atop this too, never did figure out exactly which was borking it, but the metadata was the trick for me.  It also could have been related to my ssd alignment partitioning that always gave me grief with low-level fs.

-mb

On 03/21/2012 03:19 PM, Stephen wrote:

if it boots up and sees the LVM then you should be able to customer

partition and configure without reformatting.

you can look and see a fair amount without even writing changes to the disk.

However i would still make a backup.

On Wed, Mar 21, 2012 at 1:55 PM, Nadim Hoque<nadimhoque at gmail.com>  wrote:

I currently have Centos 6 installed with software raid 0 with LVM. I was

wondering if it is possible to install Ubuntu server 10.04 with those

settings without data loss and that the current raid/lvm will stay in tact.

So far in my experience I should be able to do this, but I just wanted your

input on the matter. I might switch to ubuntu server for the vast number of

packages in the default repos and when I used it before I really liked it (I

love how the default repos have what I want, and ufw is nice as well).

--

Nadim Hoque

Undergraduate Intern

ASU Advanced Computing Center

Cell: 480-518-6235

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ASU Advanced Computing Center
Cell: 480-518-6235

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