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I tried to install ubuntu 17 on disk where was windwos 10 before. I created bootable usb with efi installation. After installation i couldn't see hdd in bios boot menu while i was in UEFI mode.(in legacy mode it showed). So i searched on Internet and then after few attempts i started ubuntu from usb and manually deleted partition table in gparted and create new one as MBR(msdos). Then i restarted notebook and run new installation with uefi mode selected (fast boot, secure boot turned off) but nothing changed. Now it boot on uefi mode but if i look to gdisk partition table is still GPT with protective MBR. Can someone explain why partition table type forced to GPT?

Disk partitions i used:

sda      8:0    0 931,5G  0 disk
├─sda1   8:1    0   8,4G  0 part [SWAP]
├─sda2   8:2    0   477M  0 part /boot/efi
├─sda3   8:3    0  37,3G  0 part /
└─sda4   8:4    0 885,4G  0 part /home
Branislav Bellovic
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  • Normally Legacy BIOS/CSM booting systems use MBR partitioned disks whereas UEFI booting systems normally use GPT partitioned disks. Windows only supports it this way, Linux should theoretically support MBR/UEFI combinations, but it's not as well tested as the standard way and may lead to problems. See https://superuser.com/q/1067709/418736 – Byte Commander Aug 25 '17 at 08:51

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First, be aware that in EFI mode, the computer doesn't really present options to boot disks; it boots files. (There are sometimes entries for disks that boot the fallback boot loader, EFI/BOOT/bootx64.efi. These are intended for use on removable media, but can be used to boot hard disks in some cases.) When Ubuntu is installed, you should see a new boot entry called ubuntu in the computer's boot manager. It could be that you got such an entry but didn't see it because you were looking for something else, in which case you created problems for yourself when you tried your second install. OTOH, it could also be that a bug in the Ubuntu installer or in your firmware caused the ubuntu entry to not be created. In the latter case, you might want to check the following questions and their answers:

The second two of those mostly apply to dual-boot setups, which I gather you don't have, so they're probably less applicable than the first one.

As to the partition issues, GPT uses more of the disk than does MBR. Thus, if you convert from GPT to MBR using tools that don't know about the GPT data structures, or that just don't bother to erase them, you'll end up with MBR with remnants of the GPT data structures. Some tools, including my own GPT fdisk (gdisk, cgdisk, and sgdisk), will notice this and offer to use the GPT data. This is an intentional design decision to aid in case of damage to the GPT data structures, but it can be confusing if you used a dumb program that didn't completely erase old GPT data structures.

As a general rule, if you boot in BIOS mode, you should use MBR on your disk(s); and if you boot in EFI mode, you should use GPT on your disk(s). Ubuntu is more flexible than this and can boot in BIOS mode from a GPT disk or in EFI mode from an MBR disk, but doing so sometimes causes problems. In multi-boot scenarios, other OSes (particularly Windows) are less flexible. For these reasons, it's best to stick to the conventional MBR/BIOS and GPT/EFI linkages.

Overall, then, I recommend you start over with GPT and EFI-mode booting. Upon reboot, if Ubuntu doesn't boot and you don't see an ubuntu entry in your firmware's boot manager, see the links above (especially the first one) for a solution. If you need more help, be sure to say what brand and model your computer is and when you bought it -- EFIs from certain manufacturers, and especially older ones (say, from 2011 and 2012) tend to be flaky and can require awkward workarounds.

Rod Smith
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