Good evening everyone. I have been struggling all weekend on this. I have no problem installing them seperately but I can't for the life of me figure out how to properly partition the hard drive and install them for a dual boot. I have been trying to be creative by installing Either Linux Mint/CentOS and installing Unubtu as a Dual Boot and then delete Ubuntu when I install the other OS. But to no avail. I also try to partition the hard drive using GParted but it will not allow me as the partition is in use (since I'm using it on the system) so it wont unmount. Is there anything I am missing? Any help is greatly appreciative. Thank you

just like you would any other dual boot setup. as you are using Linux for both OSs you only need 1 /boot partition and 1 /swap. you will need 2x /, but should be able to get away with 1 /home partition.

ex:

/dev/sda1 /boot
/dev/sda2 /swap
/dev/sda3 / <first OS>
/dev/sda4 / <2nd OS>
/dev/sda5 /home

now as more and more systems are using LVM, sadly I dont know enough about those to help point in the right direction. but that is a standard old school partition scheme that would work for a dual boot for Linux. FYI in most distros you can choose NOT to use LVM in most cases too, but LVMs to offer a great many advantages over the standard file system. ease of expansion and reduction in size for starters as well as ease of spanning or creating RAIDs on the fly much simpler via LVM then old partition schemes.

Thank you for your response. That is good to know. My only concern now is that if I install Linux Mint first, I do not get the option to dual boot when I install it with centos. Are you saying I just try to install without the LVM? I'm not too worried about having it as I want CentOS to be used as my training environment for RHCSA. Thank you again for your response.

I don't use CentOS but I believe it still used Grub Legacy bootloader while Mint uses grub2. Simplest options:

Install CentOS and select mbr for installation of the bootloader. When installation completes, reboot to test if it boots.
Install Mint (make sure you select the correct partition) and also select to install the bootloader to the mbr overwriting the CentOS code.
If you watch the progress at the end of the Mint installation, you will see 'installing bootloader' and then 'running update-grub'. This will find the CentOS install and create a menuentry for CentOS in the Mint grub.cfg file.

You could do the opposite installing Mint first then CentOS which would require your going into CentOS and finding the /boot/grub/grub.conf file and manually putting a correct entry there for Mint.

This computer has CentOS on it and a guest partition (3) used for testing other Linuxes. The CentOS bootloader goes on the MBR, that for the guest goes on the partition. In CentOS, /boot/grub/grub.conf contains an entry at the end

title guest
rootnoverify (hd0,2)
chainloader +1

while at the beginning "hiddenmenu" is deleted.