[CentOS] dual-booting <- Re: installing Cents os server 7.0

Fri Jul 3 17:08:59 UTC 2015
Chris Murphy <lists at colorremedies.com>

On Fri, Jul 3, 2015 at 4:42 AM, Timothy Murphy <gayleard at eircom.net> wrote:
> Chris Murphy wrote:
>>  Supporting dual boot means ability to boot both installed OS's upon
>> completion of installing the second. This doesn't happen when the first OS
>> is Linux using LVM, or Windows, or OS X.
> In that case, wouldn't it be more precise to say: CentOS-7 doesn't support
> dual boot if you are using LVM?

Or using Windows or OS X (just an ugly failure in that it causes XNU
to panic, but it hasn't actually injured anything, it is still
possible to boot OS X via the firmware boot manager).

> It seems to me to work reasonably well with ext4.

Correct. If the existing OS uses ext3/4 on standard partitions, then
the installer can do fs shrink, and when it calls grub2-mkconfig, the
installation is found and boot entries are created for it. That the
boot entry is distinctly sub-optimal is a long standing GRUB problem
not an installer problem and not a CentOS problem per se. But it's
still sloppy. The tools already exist for this to be done better, but
for reasons unknown GRUB upstream likes to do things the hard and sub
optimal way whenever possible.

> Does it work with LVM if you have a separate ext4 /boot partition?

No. The root fs is hidden in an inactive LV, so os-prober (via
grub2-mkconfig) won't find that Linux installation. The installer
should make all LVs active so os-prober can find other OS's and make
boot entries for them, but it doesn't.

Chris Murphy