Good Morning, all
1. Can you enter that code from my point 2 in #2 on your Ubuntu and report back? (on EFI vs Legacy)
2. Can you take eg a phone pic and upload it, of your Grub Boot Menu as it is currently?
3. Can you give us a GParted screenshot (from Ubuntu), of your "State of The Nation" (see mine below)? Either that, or the outputs of (a # precedes my comment, not an instruction)
#(those are L's) AND
sudo fdisk -l
# also an L
... will do for now.
....but now CentOs is broken.
Can you give us exact error/s?
On Multibooting - My Dell Inspiron shipped with a 256 GB SSD and a 2 TB HDD, with 16 GB RAM.
I also have a 4 TB Western Digital My Book hooked in via USB 3, with over 30 LInux Distros.
Here are a couple of screenshots.
SCREENSHOT 1 - WIZARD'S WD MY BOOK
Features 24 Linux Distros currently working happily side-by-side (going to removed /dev/sdc26 Debian, as now have one with wifi working at /dev/sdc12). I use GParted as a forward planner, and I use it daily.
Also featured is a 400 GB partition for Timeshift, which houses the snapshots for my entire system. No Downtime for The Wiz, 10 - 15 mintues with a restore and I am back in business
Note there is ... NO SWAP. Not needed, and that's a fact, not just an observation (unless perhaps you do extensive video or music editing, or a lot of Google Earth-ing). If you have 6 - 8 GB RAM, it (swap) is a waste of space.
WIZARD'S SOLID STATE DRIVE
... has Windows 10 and a further 9 LInux Distros. All work. Windows is shrunk to a bare minimum, but I may have to give it a little more space because of its incessant updates.
My /dev/sda 2 TB HDD not shown here, has 2 Legacy Linux on it for helping purposes and is currently formatted to MBR. Once I finish those experiments, I could just as easily revert it to UEFI-GPT, and throw another 50 Linux on it.
On my secondary rig, a Toshiba Satellite, I have the partitions numbering into the 50s, but with 8GB of RAM, it is getting a bit sluggish (and not because of lack of Swap, lol).
For Dan's purposes, we could regard his one drive (I take it that is so?) as being like my SSD - Windows 10, my BeaverMATE is like his Ubuntu, and my Fedora equates to his CentOS.
Virtual Machines such as VBox and VMWare have their uses, but there is a steep learning curve, easier just to do a full install.
With the VM, if you have 2GB or less of RAM, it is a waste of time, and if you have 8GB, you have to allocate at least 4GB to the Guest OS just to get an idea of performance. If Dan is prepared to do that, we have people here who can help with VM.
Once I have both working I will definitely look at Timeshift before attempting another install!
Nope, better is get one running, take a Timeshift snapshot. Get the 2nd running, take a Timeshift snapshot. Hindsight is great (not).