Haiku 32-bit installs without any apparent problems on a late 2006 polycarbonate iMac.
However, post-installation the only way I can get the machine to boot-up is
via a startup using the install DVD and the SHIFT button.
I have “fooled around” with BootLoader and MakeBootable without any joy.
I’ve just had a go with the 64-bit install with the same result.![dud|259x194]
This is “a right ^&*%$” as, in all other respects things are fine.
The uefi bootloader is not installed automatically (it’s on our todo list).bootmanager and makebootable also don’t know about it yet and work only for bios booting. You need to manually create an efi partition and copy the bootloader to it.
I think this is documented somewhere?
Ouch.
“somewhere” makes me feel uneasy . . .
Somewhere == on our website. First result when you search for UEFI 
There’s:
https://discuss.haiku-os.org/t/uefi-guide/8457
and
https://www.haiku-os.org/guides/uefi_booting/
Unrelated to booting Haiku, there’s this article if you’re curious about the whole process:
https://depletionmode.com/uefi-boot.html
OK, “On it”, expect abusive comments following. 
I didn’t have a particularly bad time when I did it. The biggest problem I had was that Haiku wouldn’t mount the EUFI partition on the install usb stick I was using so I could copy the contents over. I don’t think Linux would mount it either. I think I ended up copying it with Windows.
However, I can mount it now in Haiku so you shouldn’t have that problem.
I’m installing on a 2006 iMac so Windows doesn’t come into the picture.
Also:
"Create a small (32 MiB is more than enough) partition at the start of the disk.
“EFI system data” type.
Format as FAT32, label “EFIBOOT” "
I’m going for an EFI system format.
Is “bl**dy silly” (I warned you about abusive comments) as DriveSetup does not seem to offer FAT32 as an option.
Aha: well I can do a FAT32 format in the “second format” which is pretty misleading.
NOPE: that did not work at all.
I wonder (?) if, having got my iMac to boot from the Haiku system installed on its hard disk via the install DVD, there isn’t a way to “just” flag my Haiki partition (currently my iMac sports a UEFI boot partition that isn’t doing any good at 100MB, and the rest of the hard dsik that has Haiku installed on it) as bootable?
Certainly Bootloader doesn’t seem to be much cop.
Tried Bootloader with the UEFI partition and the Haiku partition . . . . .
Uh… You said you are using 32-bit Haiku? That doesn’t support UEFI booting. So installing the EFI loader will not help you here. You just need to tell the system menu to boot into the Haiku partition…
No. I moved onto the 64-bit install as was getting bogged down with the 32-bit version.
“You just need to tell the system menu to boot into the Haiku partition…”
Please tell me how to do that.
Every time I see the word “just” I want to tear off all my clothes and run howling through the woods! 
Well I don’t know how to do that, I don’t have a mac. 
If you are using the EFI loader then yes, you need to put the loader into the ESP. If you are just using the standard BIOS loader, then “chainloading” from the system menu, or GRUB, or rEFInd should work.
First of all . . . Macintosh computers don’t have a BIOS . . .
Intel chip computers generally have a BIOS, but as far as I know “modern” (that’s another word that makes
me want to behave oddly ) Macintosh computers (before Apple adopts the ARM chip) don’t
have a BIOS . . . put me right here if I’m wrong.
Since MacOS 10.0 the system has been a sort of tarty type of UNIX.
Ultimately this is’ bxllxcks’ as my BBC Model B, which, paradoxically, I bought in 2016,
boots without needing to be connected to the Cassette Recorder where I save files.
Have you tried the Raspberry Pi? It runs an open source version of the RISC OS. As for me, I’ve never had a BBC computer (I’m in my late 20s), but have tried to study their history.
But I have had and still use Macs 
And I happen to also play with Haiku. So I can help there. If your iMac is a Core Duo/32-bit (which could be a possibility, since it’s a 2006), your best bet is to use dd in Terminal to wipe the partition table on the hard drive, set up a legacy/Intel Partition Map or MBR table (Haiku includes DriveSetup for this), and install Haiku to disk from the DVD. The Mac should then go gray for a few seconds on next boot, but should boot up from the new install.
If it’s 64-bit (Core 2 Duo), I don’t think Macs supported 64-bit EFI until 2008, (so unless I’m wrong and Haiku has 32-bit efi), this won’t work. It’s the reason early 2008 Macs and earlier drop support after Mac OS X 10.7.5 (Lion). That said, your best bet would be to try a similar method as with 32-bit and write a legacy install to disk as the Mac has CSM (Compatibility Support Module or legacy boot support) built into its firmware.
I’m currently fooling around with a late 2006 iMac, 64-bit (mainly because I use my early 2006 32-bit iMac fro running PPC software through macOS 10.6).
I will have a go with 32-bit Haiku, again . . .
NOTE: Mountain Lion drops all Mac models pre-Y2009. Mojave/Catalina drops all Mac models pre-Y2012.
Yes, I think we just said it in two different ways. After Lion (10.7.5 was the final revision) or at Mountain Lion (10.8). Also, just in case any Mac Googlers are visiting the forum, Late 2008’s can unofficially run up to 10.9.x Mavericks with a third-party patcher.