[CentOS] Upgrading to CentOS 6

Tue Feb 25 18:02:18 UTC 2014
Johnny Hughes <johnny at centos.org>

On 02/25/2014 10:25 AM, Styma, Robert E (Robert) wrote:
> I recently built a CentOS 6 system as my main machine at home.
> With a bit of help from members of this list, it is now working
> better than the machine it replaced (RIP).
> The new machine works so well, that I would like to convert some
> CentOS 5 machines to CentOS6.
> I did some research on the web and the new install is still considered
> the proper way to upgrade CentOS.  Same as Fedora and RHEL.
> The question becomes, "What makes the Ubuntu developers so
> clever that they can do major upgrades through their apt based
> update system?"
> There must be some sort of gotcha or tradeoff involved in allowing this.
> Does anyone have any insights on why they can get away with this
> while CentOS cannot?

The reason is this ...

You could work out a procedure to do an in place yum upgrade .. it would
involve doing all kinds of stuff with python versions so that yum and
the rpm database could live through the update.

Even after you did this, most of your data would not be usable.  Because ..

In CentOS-5 to CentOS-6 look at php. You move from  php-5.1.6 to
php-5.3.3 ... almost none of the php websites would work after an upgrade.

Same for things like mysql in CentOS-4 to CentOS-5, it went from version
4.1.22 to version 5.0.95.  Lots of things required to do this upgrade to
the actual data.

So, if you upgrade in place, you get finished and you have a broken
system until you figure out how to fix all of your data and config files
.. and the difference is 3-4 years worth of in version numbers (unlike 6
months at most in a bleeding edge distro).  Skip 2 versions (EL4 to EL6)
and it is even more change (5-8 years of difference).

Distros that upgrade in place BREAK your one system and it does not work
until you figure it out.  Also, not every package in the old system
exists or has a replacement in the new system, so you have orphaned
cruft left on your machines.

If you upgrade onto another machine, you can do an install, move over
your data and configs one by one, work out all the problems and get the
fixes in, etc.  You can move services one at a time, change pointers,
never have downtime.  If you upgrade i place, BAM .. down until you
figure it all out.

I guess other distros that upgrade in place don't care that you are left
with a broken system.

If you absolutely insist to upgrade in place ... boot the new DVD for
the new version and at the command line do:  linux upgradeany

That will let you upgrade in place and end up with broken data/configs
with things that do not start, etc .. just like the other distros who do
in place upgrades.

When it breaks (it will), then you get to keep all the pieces :)

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