[CentOS] how to change distro live?

first last prelude_2_murder at yahoo.co.uk
Tue Jun 19 10:48:24 UTC 2007

--- Farkas Levente <lfarkas at bppiac.hu> wrote:

> hi,
> we've got many mandrake 8,9 and 10 system remotely. we'd like to
> remotely replace these systems to centos 5. we've 4 disk in them. one
> is
> the system drive (no need for raid) and there is free space on the
> remaining 3 disk. so what we think about:
> - download the new system to the data disks
> - install grub (mandrake has lilo) to boot the old system and reboot
> - create the old system in the data disk
> - update grub to boot the old system from the data disk and reboot
> - repartition the system disk
> - transfer the new system to the system disk
> - update grub to boot form new system disk and reboot.
> this seems to easy but has many very dangerous steps and we has only
> remote ssh access to the system. if we loose the connections we can't
> access the system anymore and we've to travel a lot! another
> constrain
> that we should have to do this very fast ie. it'd be nice if the
> system
> wouldn't be down for a long time.
> - what would be the best method for this?
> - what are the dangerous step here?
> - what would be the best way and format to transfer the new system to
> the disk (we think about an iso file)?
> - does anybody do such thing and what is his experience?
> thank you for your help in advance.

A procedure I've followed a few times is to:
1 -Install the OS in another machine (ideally, similar to what you are
going to install into)
2 -Create a partition in the new machine
3 -tar the OS you installed in 1, copy the file to the remote machine
4 - Untar the new system on the new partition (careful with not
overwriting anything)
5 - chroot onto this, change configuration (fstab, network
6 - Configure the boot loader. In this case, you have lilo, DO NOT
OVERWRITE IT YET. Reconfigure lilo to add an entry for the new system,
then run lilo with the option that marks it as "boot from this OS only
once" (I think it is -r option) so, if the system fails to boot from
the new OS, you can reboot and get your old OS. 
7 - Reboot, check that everything works. If it does, change Lilo to
boot the new OS by default.
8 - If you don't desperately need the space the old OS is on, leave it
there for the time being, maybe you will find something that doesn't
work later on. If you decide to remove the OS, make sure you install
the new bootloader (lilo requires the files to be in the exact same
location on the disk)
9 - That's all folks :)

As I said, I have used this system in the past, but I can't guarantee
that it would work for you, so be extra careful.


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