I just noticed that the report from inxi is showing that the installation utility for my fresh install of a “default” configuration, to overwrite a previous UM 20.04.5 LTS, has chosen to use MBR as the partition table format, instead of GPT.
My computer is so old that it only has BIOS, not UEFI.
But, I have installed, on the same computer, with other disks, from Ubuntu DVD ISOs, always creating GPT partition tables.
So, why this time?
Since I told the installer to overwrite the existing installation (I unplugged my other internal disks before starting the install), I would have assumed that the default for the installer would have been the more robust GPT partitioning table, and not MBR.
The oldest system I use in QA testing is a 2007 HP Compaq which is also pre-uEFI too, and I’ve been able to install all releases up to and including Ubuntu 25.10 in both GPT and legacy MBR [partition tables]. You do have some control over this by the options you give the installer (ie. erase disk and install using ubuntu-desktop-installer and I’d expect a GPT partition table to be used; if you use manual partitioning however that is up to you and you’ll mostly get MBR!, however if you use a ISO using calamares you won’t get GPT on any disk size I’ve used in QA on older non-uEFI hardware unless you force it).
You do mention Ubuntu [MATE] 20.04 LTS, which used the ubiquity installer, which could be altered [in how it worked] by how you wrote the ISO to your install media (ie. reformat ISO in write to install media) and was a rather different animal in regards what the installer does to recent releases (23.04 & newer for Ubuntu Desktop and some flavors, 24.04 & later for Ubuntu MATE) which use ubuntu-desktop-installer. Are you comparing something from long ago to the newer installer which has been used since 23.04 for Ubuntu Desktop & some flavors??.. I don’t know.
Please note: I’ve done almost no QA installs with resolute media thus far (and what I have done is possibly all with the calamares flavors too), so there could have been a change you’re seeing that I’ve not noted. Either way I’d expect (prior releases) a MBR table in some install cases on legacy hardware where it’ll work.
That is the option I chose from the menu offered by the ISO installer, so I expected an install using GPT, not MBR, even if the disk may have been previously MBR, which I can’t remember (old age being what it is ).
What I observed is what I would consider some logic by the installer deciding that MBR was the way to go … and I don’t understand why that would be the case for a physical hard drive of very standard make:
Since I don’t have much invested in that installation, I am planning to redo that, but with manual control, using Gparted from the Live ISO, before performing the install.
I just don’t understand why I have to redo the install to get the GPT on that drive. I’m just saying that I think maybe there must be some logic (which needs to be reviewed) that may have “preserved” the MBR when, for a “reformat and overwrite” directive, it should have rebuilt the Partition Table using GPT.
I run Lubuntu (24.04) which also uses a different installer (it used to be Ubiquiti, today I’m not sure).
When doing (manual) partitioning, it gives me the hint to create an unformatted 8 MB partition if I want to use GPT. Otherwise it will fall back to MBR.
This is on old BIOS laptops (2009-ish).
Perhaps that might help?
I wasn’t really looking for a fix or solution. I was flagging what I considered would be the expectation of anyone installing the Distro. As I explained in my previous response, over the next few days, for my own benefit, I plan to
boot to Live ISO,
reformat disk with new GPT partition table, and
reinstall the UM 26.04 LTS Daily Build (Nov 19, 2025)
I was primarily raising the point as to why a fresh install would ever end up with an MBR partition table, rather than the expected GTP partition table.
FYI:
Lubuntu used ubiquity on its primary ISO as installer (and debian installer on the alternate ISO) up to Lubuntu 18.04 LTS.
All releases since (and including) Lubuntu 18.10 have used the calamares installer. A total of four flavors have used calamares since then, three using it for more recent 24.04-25.10 releases.
).