Procedure to install Linux on a non-partitioned iMac

[WRONG]

Hello Forum!
I hope the title is not misleading for my question.
Basically, I got a 2011 iMac, currently with just one partition running on Sierra.
I want to install also Linux on it, hence make a partition, but this will of course erase the contents on the hard disk.
What's the best way to do that?
I presume something like this:
1 - make copy of the iMac on an external drive with CarbonCopy or SuperDuper
2 - make two partitions of the hard disk, one for Linux one for MacOs
3 - install my Mac from the copy
4 - install Linux
5 - profit!

right?
Anything more I need to know?
Thanks in advance for feedbacks!

 

[S.B.G]

This video should be helpful for you.
I've never dual-booted on a Mac before, but your plan seems reasonable. Actually, I haven't dual-booted anything since the days of Windows 98 and XP.