[CentOS] about major version upgrades

[Johnny Hughes]

On 02/07/2012 06:39 AM, Ljubomir Ljubojevic wrote:
> On 02/07/2012 07:04 AM, Mihamina Rakotomandimby wrote:
>> Hi all,
>>
>> In http://goo.gl/Krjfh I read:
>>
>>     +++++++++++++++++++++++
>>     Upgrading from CentOS-4 or CentOS-5:
>>     We recommend everyone run through a reinstall rather than attempt an
>>     inplace upgrade from CentOS-4 or CentOS-5
>>     +++++++++++++++++++++++
>>
>> Do you ever now if that advice will be up to date for the 6 to 7 upgrade?
>>
>> What is the preferred upgrade process if some want to upgrade inplace?
>> I mostly run virtual guest in a one-VM-per-service (MySQL, php, Mail,
>> DNS, NFS/SMB) basis, with a main + spare physical machine.
>>
>> I'm installing 6.2 on our dev servers and try to pre-evaluate the amount
>> of work when 7 will be released.
>>
> 6.x will be supported until 2020. Reinstalling once in 10 years should 
> not be the problem.
>
> Reinstall is ALWAYS advised, since probably many packages will be either 
> depreciated or heavily changed in version 7.0.
>
> That being said, there will always be unsupported way to upgrade from 
> one version to the next.
>
> It is Your choice in the end.
>
>

It is also a MAJORLY big deal to move from one major version to another
(ie a move from CentOS-5.x to CentOS-6.x).  This is because there is no
API/ABI compatibility between major versions like there is for minor
versions.

The php is going to be much newer, the samba is going to me much newer,
the httpd is going to be much newer, the kernel is going to much newer,
ldap is going to much newer, etc.

For example, I recently upgraded a CentOS-4 box to CentOS-5 and I went
from the CentOS-4 php to a CentOS-5 version ... I had to re-code my
applications written for the php-4.3.9 in CentOS-4 to instead work with
the php-5.1.6 in CentOS-5.  I had to rework all the mod_auth files from
httpd-2.0.x to work with mod_authz from httpd-2.2.x ... etc.

The purpose for having enterprise software is so that you can get a
return on your investment and use your code for 7 years (for CentOS
versions before CentOS-4 ... now 10 years in post CentOS-5).  But
keeping things for that period of time means that when you do need to
upgrade, the "differences" are much harder and the changes are usually
much bigger for a given package.

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