[CentOS] Upgrade from CentOS6.6 to CentOS 7

[m.roth at 5-cent.us]

Digimer wrote:
> On 15/12/15 11:10 AM, m.roth at 5-cent.us wrote:
>> Traiano Welcome wrote:
>>> On Tue, Dec 15, 2015 at 6:36 PM, Digimer <lists at alteeve.ca> wrote:
>>>> On 15/12/15 10:17 AM, Traiano Welcome wrote:
>>>>>
>>>>> Is it possible to upgrade from CentOS 6.7 to CentOS 7?
>> <snip>
>>>> Given how radically the OS changed, I would strongly advice against
>>>> it.
>>>> The move from sysvinit to systemd alone is enough to recommend against
>>>> an upgrade.
>>>
>>> So it's not possible under any circumstances?
>>
>> Let me offer you one option: *IF* you have enough space on your
>> filesystems, you could:
>> mkdir /boot/old /old
>> zsh
>> zmodload zsh/files
>> mv /boot/* /boot/old/
>> mv /usr  /old/
>> mv /lib* /old/
>> sync
>> sync
>> And go into the installer. If you have a problem, you can go back....
>
> How would the move from the old to new grub work, particularly in
> reverse if needed?

Actually, I was copying part of our internal instruction checklist for
upgrading via rsync. For that, we have one machine that's been updated to
the new release. Then, on the one to be updated, we mkdir /new /boot/new,
then
rsync -HPavzx --exclude=/old --exclude=/var/log/wtmp $machine:/. /new/.
rsync -HPavzx $machine:/boot/. /boot/new/.

After doing the zsh stuff - that loads it all into memory, and it won't
gag when you do the moves, mv /boot/. /boot/old/, and /. /old, then mv
/boot/old/new/. /boot/, and /old/new/. /

Given that, you can always mv /. /old/new, and /boot/. /boot/new, rsync,
and you're back.

Is that clear as mud? The whole idea is the os and boot is moved into the
./old, and the new into the real locations.

       mark