Am using 60% Macs and 40% PC's - all running Linux and dual- or triple -boot. 
Well, for Mac hardware running macOS/Linux or Linux/Linux or.... -
you will need a boot manager; except you are running ONE Linux only. 
Which iMac do you got running over there (looks like 10,1 from 2009) 
Dual-boot with what ?
Is there still macOS onboard - or not
It’s a 9,1 from 2007
I lost my OSX while using Live DVDs to try Linux distros before Xmas. And one Live DVD froze and I had to do a Power Off. After that, I realized that the Live DVD had started to install itself on top of my OSX on my HDD. In the end I lost everything and so I started to experiment with Linux on the Mac.
As you mentioned, I always had to rely on some kind of boot manager with my installations. At first I was always reinstalling a new version of Linux every time but last week I decided to keep Linux Mint which was working well and install another Linux version in dual-boot.
So it’s new for me to dual-boot 2 Linux on a Mac. But I already had problems with even only 1 Linux installed and not booting correctly. Now I know why...
Btw, yes, I used Refind at the beginning. But I stopped using it after a whole and tried to do it with Grub only.
if you need assistance, give a shout
Ahm, ya.... 
This is actually possible, but it needs a lot of " handcrafting" on the grub setup, which is may be too hard for an average user.
Clem from Linux Mint wrote a how to for this in their forum.
Problem: Different Macs does need different configurations to by-pass the Macs boot ROM (bios).
That said - you need to know exactly which firmware is installed and which steps in which order needs to be done to get the Mac running in dual or triple boot mode with grub.
Next problem then:
If the OS, which holds the grub part, does a kernel or grub update, it will prolly kill your former setup and you will have to start again.
Easy way out:
rEFInd boot manager is doing the job and let you just smile about this issue.
As long you you are running Mint on it only, you can deal with grub so far,
but when it comes to add another partition with a Debian based distro like Elive or MX Linux -
it prolly will fail badly.
Advise:
OK, here we go with a new topic, like
Little How To install Elive on (compatible) Apple Macintosh Computers with Dual-Triple-Boot ..... 
boot from a macOS install stick for this and blank you disk (!)
.
80GB Mac HFS+
and
60GB fat, name it Linux_1
and another
60GB fat, name it Linux_2
.
.
switch the Mac off...
.
YOU SEE THE BOOT CHOOSING SCREEN, then release the option key
.
(depends on your model/firmware)
.
(here in this example it would be: 60GB fat, Linux_1, probably: /dev/sda4)
choose in the partition dialogue:
"something different" (Mint/Ubuntu based distros)
{then recommend install, when it comes to
"where you want to install grub?" - choose the partition where Linux is located -
NOT ON THE BEGINNING OF THE DISK}
for Debian based distros like Elive and MX Linux
you need to choose the target partition manually -
DO NOT CHOOSE : AUTOMATICALLY
After this you can do the same way adding another optional Linux installation (e.g. 60GB Linux_2)
.
YOU SEE THE BOOT CHOOSING SCREEN, then release the option key
and choose the macOS partition, boot
.
you can get it from here – btw for all platforms:
Note:
You will need a second Computer with an internet connection
and
a relaxed free day ….
Interesting... but this would be to re-install OSX, which I don’t have???
Btw, I searched for a Leopard installation disk, without success, which was the original version installed, and go from there. I stopped searching after a while and just installed only Linux Mint...
which iMac do you got ------- important to know --------
(if you don't know - check the serial number located under the stand (foot)
and send it via pm to me)
Btw:
Leopard is quite obsolete and a bit poor on features,
but SnowLeopard is the masterpiece from Apple yet, a must have...
I am affraid, if your iMac came with Leopard, you will have may be
an IntelCore Duo, but not an IntelCore 2 Duo and therefore a 32bit machine - so reply.....
Missing part of the post... 
Can’t remember what...
the serial number is located under the stand .....
EDIT:
So, @gtech's iMac specs are known by now:
I've got same machine here and so my advise is as follows:
OS X 10.11 "El Capitan" is the latest supported OS X by this iMac, but not supported from Apple anymore... no need to add it.
I would install SnowLeopard instead, for having maximum of backwards compatility, so you can run old and awesome apps, too.
For daily use and productivity - install additionally Linux
and manage the boot process with rEFInd,
or just press the option key during every boot.
Erase the disk, writing zeros (takes a night or so...) - much better -
if you can (...) install a SSD - I did it, the effect is magic -
like a brand_ 
machine afterwards 
With those actions I brought this computer to a new life
never feeling it would be slow or old, it's the opposite.
.
.
@Thanatermesis ,
may be we should move these posts to a new category,
like HowTo install Elive on Mac hardware ...
He does not necesarily have to if he has nothing to hide!
@stoppy98
Actually the disk will be faster afterwards, especially in his case
How will it be?
@stoppy98:
With this procedure, a so called Mid-Level-Format, all hidden partitions, Mac sub-filesystem, boot entries, orphans and NODES will be erased and the disk structure got rebuild by the controller.
Alas a low-level-format is not possible with home brew,
so this is best what we can do on a user lever, where we actually are.
When it comes to deal on a hardware level,
with SCSI it is different, there you could do a low-level-format,
but not with the SATA protocol as long we can not touch the disks firmware; exceptions are specialists, which can access the disks controller directly by certain software and got the firmware for a transfer handy.
Just as a by the way explanation .... 
In @gtech's case necessary, because the disk was in use by different HFS and HFS+ filesystems, and has some orphan entries from his several interrupted installs (especially Elive/Debian are rough with creating own entries, e.g. UEFI)
for further information see:
(mainly the section: " Disk formatting process")
.
__________________________ 
@Thanatermesis , it could be indeed moved to a new category.
My goal is to re-install OS-X on my Mac, and then dual-boot Elive on it. But OS-X must be installed first...
Thanks for the infos. I don’t feel like installing a SSD for now, but it could change in the future. Not because of the cost, but because of the work...
I spent more time searching about this subject today and came to the same conclusion. Snow Leopard would be the best first move, and the easiest one to install.
I am doing some tests right now about making a bootable USB OS-X from Linux... and I am learning about Linux at the same time. My brain slowly started to work again after many years away from computers. You don’t learn a lot using iPads these days
Step 1 started... I am presently installing Snow Leopard on the first half of my 640G HDD...
I just saw that Elive 3.8.5 was ready... so you know what will be installed on the second half
But first, I have to finish installing OS-X on the Mac. Then if all goes well with the set-up, I’ll be done for tonight, because it will be too late for the second part.
More to come...
Don't forget to update OS X to 10.6.8 and also check for the latest firmware update, relating to your specific model (9,1). It is so to say kinda bios for your Mac. You will need it especially for dual boot.
Usually you can get it by the OS X application "Software Update", it is to find under the Apple icon on the left inside the upper Menu Bar.
.
Since you got a free part of approximately 320GB of your entire HD,
it is a good idea to have a third partition ready for a stable release.
Keep in mind, that the 64bit Elive ist still on beta status and in testing,
therefore it would be good to have another stable one, too.
.
For doing it at this stage
just start 'disk utility' from OS X and add another partition to your 320GB empty half part of your disk and name it wisely,
e.g. 'hd-p3' or so, for that you can identify it later easily. 
Afterwards you would have 3 partitions;
1st part with OS X SnowLeopard with approximately 160GB
2nd part for Linux with approximately 160GB
3rd part for Linux with approximately 160GB
.
160GB space for each of them is more than enough ....
.
.
EDIT:
since I needed some assistance in mathematics from several forum members,
I have to correct this as follows:
1st part with OS X SnowLeopard with approximately 320GB
2nd part for Linux with approximately 160GB
3rd part for Linux with approximately 160GB
.
Thanks for your patience with me ... 
I can imagine .... 
Last night, I ended up installing up to OS-X Mavericks. This is the latest version I found that I liked, both for the look and the specs, etc...
Today, I installed Elive 3.8.6 on the 2nd partition and installed refind as a Boot Manager.
I made a few mistakes in the formatting step but it works and will surely redo the whole process after a while to experiment a few things... it’s part of the fun.
The OS-X installation following the formatting of the Hard Disk is where it is easy to make mistakes. It was easier to install 2 Linux partitions the first time I did...
Referring to this thread I'm about to undertake installing Elive on a Macbook Air (early 2015) , just to see how mac hardware handles Elive. Done something like that before, but that was within VMWare-Fusion.
Now I got the 64bit its going to be more interesting. macOS is nice but somewhat static whereas Elive is VERY addictive and I love it!!! I let you know how it goes.
Elive on Macbook Air; wifi works OOB and running fast on a NVMe 1 TB
Once you got Mavericks installed, do a TimeMachine backup, then you always can fallback just in case, something goes wrong. I got several TimeMachine backups and they work like a treat!!!!
That was exactly my situation too... except that I lost OS-X by mistake... without a recent backup...
I have Linux Mint stable on another Mini PC that I also found boring after a while, so here came Elive 
And this time, I WILL make a backup
