I decided to install Haiku alongside the amazing WindowMaker live on my Thinkpad. I installed using the software installer and ... it didn't boot.
I was really not expecting it to replace grub automatically, but I was hopeful. The live usb gets directly into a installer which says "Complete" and "Restart"
Anyway, if you are not installing on a super old laptop, your laptop probably supports UEFI. For that, you need to follow this guide: https://www.haiku-os.org/guides/uefi_booting
Please follow the steps in order. I followed out of order and it didn't work. I guess something is done depending on a previous step - or it was just coincidence.
To configure grub, follow this guide: https://www.haiku-os.org/guides/booting/
As I am also running Linux, instead of coying the file as BOOTX64.EFI, I copied as HAIKU.EFI and used this name in the grub configuration /etc/grub.d/40_custom, getting:
menuentry "Haiku" {
load_video
insmod part_msdos
insmod chain
search --fs-uuid --set=root <EFIBOOT partition UUID>
chainloader ($root)/EFI/BOOT/HAIKU.EFI
}
and sudo update-grub2 to update grub.
I hope it helps.