[CentOS] What happened if install a el7 package on a el6 system

Tue May 7 14:20:08 UTC 2019
Valeri Galtsev <galtsev at kicp.uchicago.edu>

On 2019-05-07 04:50, Stephen John Smoogen wrote:
> On Tue, 7 May 2019 at 04:06, wuzhouhui <wuzhouhui14 at mails.ucas.ac.cn> wrote:
>> Hi,
>> Recently, I encountered a interesting phenomenon that CentOS 6.3
>> running as normal even if I (my colleague, actually) installed a
>> kernel that build for CentOS 7.x (e.g. kernel-3.10.0-327.el7.x86_64.rpm).
>> I found kernel is mismatch accidentally when I using "uname -r" to
>> check kernel version. So my question is what the harmness we will
>> get if I install a el7 rpm into a el6 system?
> Many CentOS-7 packages will not install because they will need dependencies
> that the EL-6 does not have. The kernel is different because it is mostly
> self-contained and meant to be parallel installed. In most cases, it should
> result in an unbootable system because the boot is going to be
> dracut+systemd bits and the EL-6 has none of that.

One needs to rebuild (recompile) everything that was not built on 
"mismatched" version of the system. And this will constitute correct 
"installation using old UNIX way". Otherwise you quite likely will have 
problems (even if they are hidden, i.e. if it appears to you that "all 
works"). One of examples would be using some library that is of 
different version than your extra software was compiled against. The 
library might be found, and successfully loaded at an execution time, 
but it may have different subroutine entry names or some missing which 
may be discovered only under some circumstances. At a compilation time 
the headers will be what provides necessary information... Anyway, 
understanding this will tell you apart as a sysadmin from "non-sysadmin" 
person ;-)

>> Thanks.
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Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247