Re: [CentOS] Differences from upstream RHEL

[Andrew Holway]

In my experience software compiled for RHEL "just work" with Centos and I
don't remember any case where it didn't. I have however heard whisperings
on a grapevine that RH may want to try and make future versions of Centos
slightly incompatible with RHEL but these are probably just whisperings.

If you software vendor will not support Centos as RHEL then they probably
need a good LARTing.

On 11 November 2015 at 22:52, J Martin Rushton <
martinrushto...@btinternet.com> wrote:

> -BEGIN PGP SIGNED MESSAGE-
> Hash: SHA1
>
>
>
> On 11/11/15 15:17, Edward Ned Harvey (centos) wrote:
> >> From: centos-boun...@centos.org
> >> [mailto:centos-boun...@centos.org] On Behalf Of Devin Reade
> >>
> >> The above answer is right-on.  From a technical perspective, you
> >> can probably expect the 3rd party software to work exactly the
> >> same on RHEL and CentOS (barring some implausible edge cases),
> >> however your 3rd party vendor may refuse to support you at all if
> >> you're using something that's not on their supported platforms
> >> list.
> >
> > Hehehe, for what it's worth, I encountered one of those edge cases
> > a few years ago. Dell OMSA, at least in the days of Centos 4, was
> > distributed as a self-extracting binary, that would read the
> > contents of /etc/redhat-release and compare it against a list of
> > predefined strings, and then refused to operate. The workaround was
> > to hack /etc/redhat-release.
> >
> > But anyway. That's pretty unusual. Thanks...
> >
> IBM do something similar with GPFS.  You have to tell it you are using
> RHEL when you are on CentOS.
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Re: [CentOS] Differences from upstream RHEL

[Peter]

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On 11/13/2015 09:17 PM, Andrew Holway wrote:
> In my experience software compiled for RHEL "just work" with Centos
> and I don't remember any case where it didn't. I have however heard
> whisperings on a grapevine that RH may want to try and make future
> versions of Centos slightly incompatible with RHEL but these are
> probably just whisperings.

Unmitigated rumors.  Until someone official says otherwise there is no
case where CentOS will ever purposefully be made incompatible with
RHEL.  There are some very minor edge cases where it can happen
incidentally due to:

1.  Certain identifying information being changed from RedHat to
CentOS such as the previously mentioned issues where software vendors
explicitly check the redhat-release file and refuse to run if it says
CentOS.

2.  The build process for RedHat is not known and so it is highly
unlikely that the CentOS build process replicates the RedHat one to
the degree needed for full 100% compatibility.

That said, if you find any case where CentOS acts differently to RHEL
with the same packages (and versions) installed in both then please
file a bug report with CentOS as as this would likely constitute a bug
in CentOS and should be fixed if at all possible.

> If you software vendor will not support Centos as RHEL then they
> probably need a good LARTing.

If it runs on RHEL it should run on CentOS as well.  I would fault a
software vendor who explicitly checks the redhat-release file to
exclude CentOS from running, but I don't fault them for not wanting to
support their software on CentOS, that is a choice they make.

At the end of the day when you run proprietary software you are fully
subject to the whims of the software vendor, I never understood how a
commercial business would not only voluntarily put themselves into
such a position but often times want to seek it out over the freedom
that FOSS offers.  Anyways, the vendor is also free to support
whatever OS they want, and you're free to choose not to use their
software.


Peter
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Re: [CentOS] Differences from upstream RHEL

[Edward Ned Harvey (centos)]

> From: centos-boun...@centos.org [mailto:centos-boun...@centos.org] On
> Behalf Of Peter
> 
> Anyways, the vendor is also free to support
> whatever OS they want, and you're free to choose not to use their
> software.

Except when you're not. Because for whatever reason, the choice of software you 
(the sysadmin) will support is determined by the users (engineers, financial 
people, whatever) who use the software. And the software vendors publicize 
which OSes are "supported" to run their software.

As mentioned previously in this thread, the software in question is Cadence EDA 
software, which I've supported many times on Centos before, but they do all 
their development and testing on RHEL, SLES, Solaris, and a few other 
commercial OSes, so they cannot say they support Centos. If you encounter any 
fringe incompatibility cases, because of running Centos, it's your 
responsibility. But they're not intentionally manufacturing any such cases into 
their software.

I'm comfortable with this. Even staking my reputation on it. But I brought up 
the questions because I need to make other people comfortable with it too.

I got all the answers I need - Thanks everyone for your help.
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Re: [CentOS] Differences from upstream RHEL

[Edward Ned Harvey (centos)]

> From: centos-boun...@centos.org [mailto:centos-boun...@centos.org] On
> Behalf Of Johnny Hughes

Thanks for the explanation. Of course what I want to do is evaluate centos 
fitness for our purposes, without the effort of evaluating all the changelogs, 
and I think this answer is the best possible way to approach that.
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Re: [CentOS] Differences from upstream RHEL

[Edward Ned Harvey (centos)]

> From: centos-boun...@centos.org [mailto:centos-boun...@centos.org] On
> Behalf Of Peter
> 
> You can see better details of what has been changed by looking at the
> changelog for a particular package.  CentOS changes will be at the top
> of the changelog, so again using httpd as an example:
> $rpm -q --changelog httpd

Thanks, this gives me a fair bit of work, but it's as reasonable as I could 
possibly expect.
That works.  :-)
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Re: [CentOS] Differences from upstream RHEL

[Edward Ned Harvey (centos)]

> From: centos-boun...@centos.org [mailto:centos-boun...@centos.org] On
> Behalf Of Devin Reade
> 
> The above answer is right-on.  From a technical perspective, you can
> probably expect the 3rd party software to work exactly the same on
> RHEL and CentOS (barring some implausible edge cases), however your
> 3rd party vendor may refuse to support you at all if you're using
> something that's not on their supported platforms list.

Hehehe, for what it's worth, I encountered one of those edge cases a few years 
ago. Dell OMSA, at least in the days of Centos 4, was distributed as a 
self-extracting binary, that would read the contents of /etc/redhat-release and 
compare it against a list of predefined strings, and then refused to operate. 
The workaround was to hack /etc/redhat-release.

But anyway. That's pretty unusual. Thanks... 

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Re: [CentOS] Differences from upstream RHEL

[J Martin Rushton]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1



On 11/11/15 15:17, Edward Ned Harvey (centos) wrote:
>> From: centos-boun...@centos.org
>> [mailto:centos-boun...@centos.org] On Behalf Of Devin Reade
>> 
>> The above answer is right-on.  From a technical perspective, you
>> can probably expect the 3rd party software to work exactly the
>> same on RHEL and CentOS (barring some implausible edge cases),
>> however your 3rd party vendor may refuse to support you at all if
>> you're using something that's not on their supported platforms
>> list.
> 
> Hehehe, for what it's worth, I encountered one of those edge cases
> a few years ago. Dell OMSA, at least in the days of Centos 4, was
> distributed as a self-extracting binary, that would read the
> contents of /etc/redhat-release and compare it against a list of
> predefined strings, and then refused to operate. The workaround was
> to hack /etc/redhat-release.
> 
> But anyway. That's pretty unusual. Thanks...
> 
IBM do something similar with GPFS.  You have to tell it you are using
RHEL when you are on CentOS.
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Re: [CentOS] Differences from upstream RHEL

[Peter]

On 11/11/2015 09:03 AM, Edward Ned Harvey (centos) wrote:
> At work, we use some commercial software, that names RHEL6 as a
> supported OS, but not Centos6. I would like to know the difference
> between Centos and RHEL, in order to claim (or not) that we can
> support our users on Centos instead of RHEL.
> 
> I see the release notes, that say "Packages modified by CentOS," but
> it's not clear what the modifications are. I have been browsing
> around for these details, and have not yet found specifics of *what*
> was modified in those packages.
> 
> Can anyone please direct me toward details of what's modified in the
> packages that centos modifies? 

Mainly branding changes, as well as other minor changes to make things
work with the CentOS infrastructure, eg replacing redhat-release with
centos-release to point to CentOS package repositories instead of the
RedHat ones.

You can tell which packages were modified because they have the word
"centos" in the release number, eg: "rpm -q httpd" (use repoquery
instead of rpm if you don't have the package installed yet) shows this:
httpd-0:2.4.6-31.el7.centos.1.x86_64

You can see better details of what has been changed by looking at the
changelog for a particular package.  CentOS changes will be at the top
of the changelog, so again using httpd as an example:
$rpm -q --changelog httpd
* Mon Aug 24 2015 CentOS Sources  - 2.4.6-31.el7.centos.1
- Remove index.html, add centos-noindex.tar.gz
- change vstring
- change symlink for poweredby.png
- update welcome.conf with proper aliases

...

Note that it is possible for there to be changes that aren't listed in
the changelog, nobody's perfect.  If you want to know for sure exactly
what has changed then look up the package on git.centos.org.


Peter
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Re: [CentOS] Differences from upstream RHEL

[Devin Reade]

--On Tuesday, November 10, 2015 12:53:20 PM -0800 Gordon Messmer 
 wrote:



That depends on what you mean by "support."

It's almost certainly possible to run the binaries on CentOS, but if you
need any technical support from the vendor of that application, they
might not provide it.  Your first step should be to talk to them directly
and find out what level of support is available for CentOS.  Then decide
whether or not that's a deal breaker.


The above answer is right-on.  From a technical perspective, you can
probably expect the 3rd party software to work exactly the same on
RHEL and CentOS (barring some implausible edge cases), however your
3rd party vendor may refuse to support you at all if you're using
something that's not on their supported platforms list.

That is assuming you're using mostly base CentOS or only repositories
that are known to not conflict with base.  See the CentOS wiki for
details.

If they sign off on it, get it in writing (or save and print off that
email).

Even if they do, you should still be using a UAT environment to satisfy
yourself and provide due diligence.

Devin


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[CentOS] Differences from upstream RHEL

[Edward Ned Harvey (centos)]

At work, we use some commercial software, that names RHEL6 as a supported OS, 
but not Centos6. I would like to know the difference between Centos and RHEL, 
in order to claim (or not) that we can support our users on Centos instead of 
RHEL.

I see the release notes, that say "Packages modified by CentOS," but it's not 
clear what the modifications are. I have been browsing around for these 
details, and have not yet found specifics of *what* was modified in those 
packages.

Can anyone please direct me toward details of what's modified in the packages 
that centos modifies?
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Re: [CentOS] Differences from upstream RHEL

[Johnny Hughes]

On 11/10/2015 02:03 PM, Edward Ned Harvey (centos) wrote:
> At work, we use some commercial software, that names RHEL6 as a supported OS, 
> but not Centos6. I would like to know the difference between Centos and RHEL, 
> in order to claim (or not) that we can support our users on Centos instead of 
> RHEL.
> 
> I see the release notes, that say "Packages modified by CentOS," but it's not 
> clear what the modifications are. I have been browsing around for these 
> details, and have not yet found specifics of *what* was modified in those 
> packages.
> 
> Can anyone please direct me toward details of what's modified in the packages 
> that centos modifies?

CentOS changes branding (in the source code) to comply with Red Hat's
trademark requirements.

In general we do not make changes to the base os other than those
branding changes before we rebuild the source code.  We also take out
links to their Red Hat Network and instead do updates from our CentOS
Mirrors.

However, we build the source code in our closed build system on CentOS.
 Red Hat has their own closed build system that contains RHEL packages
in which they build.

This means that CentOS is not 'exactly' the same as RHEL .. so, not a
clone.  It SHOULD be functionally equivalent (ie, same commands, same
services).

CentOS also rebuilds the source code for updates that are released by
Red Hat .. however we do not provide any 'software assurance' or
guarantees for fitness of the software.  We just rebuild the source code
in the order it is released .. nothing more.

If you require commercial support from an entity that releases software
certified to run on RHEL, you need to ask them if they support said
software on CentOS.  Regardless of if they support it .. CentOS provides
NO guaranteed support of any kind.  If you require Service Level
Agreement type support (updates within a certain amount of time, bugs
fixed, etc.) then that is what RHEL is for.

If CentOS works for you and you want to use it, that's why we build it
.. but if you require some sort of assurance of fitness, especially some
sort of guarantee of timeliness for response to bugs, etc .. then CentOS
might not be what you are looking for.



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Re: [CentOS] Differences from upstream RHEL

[Gordon Messmer]

On 11/10/2015 12:03 PM, Edward Ned Harvey (centos) wrote:

At work, we use some commercial software, that names RHEL6 as a supported OS, 
but not Centos6. I would like to know the difference between Centos and RHEL, 
in order to claim (or not) that we can support our users on Centos instead of 
RHEL.


That depends on what you mean by "support."

It's almost certainly possible to run the binaries on CentOS, but if you 
need any technical support from the vendor of that application, they 
might not provide it.  Your first step should be to talk to them 
directly and find out what level of support is available for CentOS.  
Then decide whether or not that's a deal breaker.

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