[CentOS] Installing CentOS-7 but keeping CentOS-6.5

Tue Jul 15 09:22:56 UTC 2014
Timothy Murphy <gayleard at alice.it>

Ted Miller wrote:

>> I'm having trouble installing CentOS-7 on my HP MicroServer.
>> I've tried with KDE LiveCD and Netinstall (both on USB sticks),
>> and now I'm going to try with the DVD ISO.
>>
>> But I want to be quite sure I can return to CentOS-6.5
>> if things go wrong, so I'm wondering what precisely I need to copy
>> (eg the MBR and a bit more) so that I could get back to things as they
>> were. Is this documented anywhere?

> You asked what to keep to be able to boot C6.  From your narrative, it
> seems that the legacy grub boot for C6 is already gone (blown away) by
> your
> C7 install.  I haven't figured out enough about grub2 to be able to tell
> you how to preserve your current grub2 configuration, but here are some
> possible ways to keep C6 accessible:

Thanks very much for your comprehensive reply.
 
> 1. The Super Grub2 Disk from seems to be
> pretty good at finding any and all possibilities for booting using new and
> old versions of grub.

I've downloaded this and will try it if necessary.

> 2. If you are reinstalling into exactly the same location as your previous
> C7 attempts (same devices for boot and root), just don't let the installer
> update the boot information.  Since you know it boots both versions now,
> it should still boot both versions after the install.

Yes, I'll try that - though I don't remember being asked
if I wanted to update the bootloader - I probably missed it.

> Not knowing what your installation problem is, I can't tell (and you may
> not be able to tell either) if anything is wrong with your boot
> information, or if that is OK.

I'm pretty sure it gets through the code in the boot,
since it says 
  [OK] Reached target Initrd Default Target

> 3. From C3, install legacy grub onto a USB stick, which would allow you to
> boot directly to C6, without any requirement for anything to be on a hard
> drive.

I'm not sure what you mean by C3?
I see that my CentOS-6.5 system has entries in grub/grub.conf
which don't seem very old (January this year).

I did wonder if one can in fact use grub with CentOS-7,
since it seems to create an empty (almost) /boot/grub/ folder?

> 4. It is also possible to set up a CD that will boot your computer, but I
> don't remember the details of that.

Not quite sure what you mean by this?
 
> Hope one of these, or something someone else chimes in, will help you.
> Also hope you get the C7 install figured out.  So far I have only done it
> from DVD, and those went well for me.

I've found a second hard disk (from an old server) and put that in,
so I'll be able to experiment with that,
without worrying about what it does to my current CentOS-6.5 system.

Also I used to use the old grub interactively -
I'll see if it is still possible to do this with grub2.

And I'll try a couple of your suggestions first,
like not installing the boot-loader.




-- 
Timothy Murphy  
e-mail: gayleard /at/ eircom.net
School of Mathematics, Trinity College, Dublin 2, Ireland