[CentOS] Crazy thought about upgrading to new major release

[Bowie Bailey]

On 6/6/2017 5:29 PM, m.roth at 5-cent.us wrote:
> Jerry Geis wrote:
>> I have older systems out there that work fine, just for what ever reason
>> would be great to upgrade from a C5 -> C7 (due to no longer supported) or
>> C6 > C7 (for updated packages).
>>
>> Sounds like the upgrade tool is not quite an option...
>> I was thinking...
>>
>> What would be wrong with any "easy" script that did the following:
>>
>> 1) Removed all packages with the --justdb option.
>> 2) Import the RPM-GPG-KEY-CentOS-7
>> 3) install the centos-release-7.3.1611 ... rpm
>> 4) yum -y upgrade
>> 5) yum groupinstall "GNOME Desktop"   (for example)
>>
>> and reboot of course.
>>
>> Does that have any chance or working and be valid?
>>
> I know I've posted what we do here to upgrade one system from another
> before, but not in a few years.
>
> mkdir /new
> mkdir /boot/new
> rsync -HPavzx --exclude=/old --exclude=/var/log/wtmp
> --exclude=/var/log/lastlog $machine:/. /new/.
> rsync -HPavzx $machine:/boot/. /boot/new/.
> rsync -HPavzx /etc/sysconfig/network-scripts/ifcfg-eth*
> /new/etc/sysconfig/network-scripts
> rsync -HPavzx /etc/sysconfig/hwconf /new/etc/sysconfig
> rsync -HPavzx /boot/grub/device.map /boot/new/grub/
> rsync -HPavzx /etc/udev/rules.d/70-persistent-net.rules
> /new/etc/udev/rules.d/
> find /new/var/log/ -type f -exec cp /dev/null {} \;
>
> Fix /new/etc/fstab, ESP if you use UUID. I *strongly* prefer LABEL=
> Then, any webserver stuff if the old was running it.
> If this system is using Linux RAID,
>
>   rsync -HPavx /old/etc/md.conf /etc/
>
> If yuo want to, copy the original SSH keys:
>
> rsync -HPavzx /etc/ssh/ssh_host* /new/etc/ssh
>
> Don't forget /boot/grub/device.map, and for C6, /new/boot/grub/grub.conf
> is right, or for C7, /new/boot/grub2/grub.conf is good.
>
> NOTE this will work for identical machines. Otherwise, BEFORE you rotate
> ou may need to run "mkinitrd" for the latest kernel if the hardware is
> different between the machine you are upgrading and the machine you made
> the copy.
>
> mount --bind /dev /new/dev
> mount --bind /sys /new/sys
> mount --bind /proc /new/proc
> mount --bind /boot/new /new/boot
> chroot /new
> cd /lib/modules
> VER=$(ls -rt1 | tail -1)
> echo $VER
> mkinitrd X $VER
> mv X /boot/initrd-$VER.img
> exit
> umount /new/dev /new/sys /new/proc /new/boot
>
>
> Then rotate:
>
> zsh
> zmodload zsh/files
>
> cd /boot
> mkdir old
> mv * old
> mv old/lost+found .
> mv old/new/* .
>
> # Root partition.
> cd /
> mkdir old
> mv * old
> mv old/lost+found .
> #mv old/root . -- WHY?
> mv old/scratch .
> mv old/new/* .
>
> sync
> sync
>
> And reboot. If there are issues with grub, get it up from the grub shell,
> then grub-install or grub2-install as appropriate.

Interesting process.  As far as I can tell, this keeps very little of 
the configuration from the old system.  You would still have to 
re-install and copy the configurations for any necessary packages along 
with any crontab entries that were on the old system.

Other than reducing downtime, what are the advantages of doing this 
rather than just building the new OS onto a new hard drive and then 
copying things over?

-- 
Bowie