Hello fellow Slackers,
I want to dualboot Slackware and FreeBSD (I know, I know) using grub2. The OS are on different drives. I installed Slackware and grub, and edited 40_custom with my FreeBSD parameters, then grub-mkconfig -o /boot/grub.grub.cfg. Next I installed FreeBSD 12.0 on a second HD. When I boot I get the FreeBSD bootmanager; it has somehow overwritten or overridden the grub bootloader. When I uninstall FreeBSD the grub menu appears on reboot. So...how do I bypass FreeBSD's bootloader and use grub instead? Did my FreeBSD install over-write the MBR? (sorry forgot to mention I have older hardware and can only use MBR and no GPT; also UFS on FreeBSD). It must not have since I get grub back when I uninstall FreeBSD. There was no option to install FreeBSD without a bootloader. I know I've gotten this to work successfully in the past but can't remember what I did. What am I missing? Can I somehow delete the FreeBSD bootloader? I did quite a bit of searching but couldn't find where people had installed the OSs on separate drives. Thank you! Jim

If you can't boot into Slackware, boot with a slackware DVD and jump start your system using it as your boot loader. e.g. it tells you what to do right above the prompt when you boot with one:

huge.s root=/dev/sd?? noinitrd

Then simply reinstate grub again in the MBR.

grub-install /dev/sda

or whatever your boot device is.

P.S. When booting FreeBSD from lilo or grub I used to just chainload it like a Windows partition so that should work if you've already set that up in grub.cfg, after putting grub's MBR component back.

Probably your BIOS is set up to try to boot first off the drive where FreeBSD is installed and only if that fails on the drive where Slackware is installed. This can usually be changed from the BIOS setup menu.

I second check you bios to see if you can change the boot order. If that isn't possible for what ever reason maybe open the case and swap the cables on the drives.

Thanks Everyone,
Turns out it was the boot order in the BIOS(!) Once I changed the boot order to have the Slackware disk boot first, it booted into grub and I was also able to access my
FreeBSD system. The fact that when I removed FreeBSD that the machine booted from grub on the Slackware disk should have indicated to me that the MBR had not been overwritten (good idea though TheRealGrogan). I'm marking this one solved. Thanks again - LQ rocks!!

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