[SOLVED] multiple OSs and GRUB2

nix84 · 07-15-2015, 07:32 PM

Preparing to install several distros on my external USB drive. Curious about GRUB2.
Should I install each OS in reverse order of likely use in order for successive GRUB2's to capture the existence of prior installs? Or is that even how it works?

Head_on_a_Stick · 07-16-2015, 02:22 AM

I recommend that you make sure that the installer does *not* install a bootloader and then reboot into the original distribution afterwards and run:

Code:

# update-grub

To generate a menu entry for the new distribution.

The key is that the last distribution to install GRUB "controls" the bootloader -- ie, the configuration file in that distribution is the file that is parsed by the bootloader.

syg00 · 07-16-2015, 03:02 AM

update-grub is a Debian-ism - not available in all distros.

Having once had the installer (Anaconda as it happens) refuse to install a kernel if you chose to not install the boot-loader, I am a little gun-shy of this now. I allow all systems to install a loader, but install the "favourite" system last - and boot into it to run mkconfig when the need arises.
As is usual in this namespace, more than one way to do it.

berndbausch · 07-16-2015, 06:12 AM

Just a few days ago, I installed Ubuntu 14.04 on a system that had Centos 7.1. The Centos boot menus where totally messed up as a result - what was labeled "rescue" was the normal kernel and vice versa, and they ended up with the wrong root device.

I would create the final grub config file manually, or keep copies of the intermediate grub config files as you progress with you installs. As a minimum, check everything when you are done.

Changing the order of the menuentry clauses shouldn't be a big deal.

nix84 · 07-17-2015, 01:12 AM

Thanks to all -- BIG help!

RockDoctor · 07-17-2015, 07:25 AM

Here's my recipe for dealing with the situation:

Code:

 Install 1st distro with separate boot partition mounted at /boot and grub2 in MBR
 Unmount /boot, remount in /mnt/Boot
 Copy everything in /mnt/Boot to /boot
 Install grub in 1st OS's boot sector
 Manually modify grub.cfg in boot partition to chainload 1st OS's bootloader
 While additional OSs remain to be installed:
  Install next distro in new partition (with grub in this partitions boot sector)
  Manually modify grub.cfg in boot partition to chainload this OS's bootloader