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                        *edited since oldfred's comment*

Trying to dual boot

Asus G74Sx

 - EFI Enabled
 - No fast boot option

Upgraded from Win 7 to Win 10

 root@ubuntu-mate:/home/ubuntu-mate# fdisk -l

[... loops ]


Disk /dev/sda: 256.17 GiB, 275064201216 bytes, 537234768 sectors
 Disk model: Crucial_CT275MX3
 Units: sectors of 1 * 512 = 512 bytes
 Sector size (logical/physical): 512 bytes / 512 bytes
 I/O size (minimum/optimal): 512 bytes / 512 bytes
 Disklabel type: dos
 Disk identifier: 0x1db352ee


Device     Boot     Start       End   Sectors   Size Id Type
 /dev/sda1  *         2048   1026047   1024000   500M  7 HPFS/NTFS/exFAT
 /dev/sda2         1026048 535446605 534420558 254.8G  7 HPFS/NTFS/exFAT
 /dev/sda3       535447552 537229311   1781760   870M 27 Hidden NTFS WinRE
Stephen Boston
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    Your sda is MBR(msdos). Most Windows 7 installs were BIOS, but a few were UEFI. And Windows only installs in UEFI boot mode to gpt drives. Which drive are you trying to install to. Ubuntu's Ubiquity want to put grub's efi boot files on first drive. Windows fast start up must also be off, different than fast boot in UEFI setting.https://askubuntu.com/questions/913716/dual-boot-on-separate-drives-best-configuration – oldfred Jan 06 '21 at 18:23
  • @oldfred Installing to sda the installer's default. No 'fast' settings available – Stephen Boston Jan 06 '21 at 20:45
  • If installing to sda and want Windows in BIOS/MBR mode on sda, you have to install Ubuntu in BIOS boot mode. You cannot have both UEFI & BIOS on same drive. While technically you can on two drives or move boot flag & UEFI/BIOS settings each time, that is not recommended & big hassle. If UEFI system, better to also have Windows in UEFI mode but that is a total new install. How you boot install media, UEFI or BIOS is then how it installs. – oldfred Jan 06 '21 at 21:41
  • @oldfred I have tried running with EFI disabled but the system then does not pick up the EFI on the installer. Is there a BIOS installer for 20.10? I'm missing something here and don't know what it is – Stephen Boston Jan 06 '21 at 21:47
  • How are you creating Installer? Some like Rufus create an installer that is UEFI only UEFI/gpt or BIOS only CSM/MBR. Most create installer as either one, but then you have to choose in UEFI one time boot. You then should have two entries one clearly UEFI and other not like: UEFI:XXX or XXX where XXX is name or label of flash drive. If you want UEFI on sda, the change to gpt which you should use will erase drive. Be sure to have good backups. But Ubuntu will let you install in UEFI mode to MBR, but that creates other issues. – oldfred Jan 06 '21 at 22:29
  • @oldfred Ah! I used dd from the iso. I'll look into burners with more options. – Stephen Boston Jan 06 '21 at 22:37
  • The dd should work & create an installer for both UEFI or BIOS, but this is a bit safer & uses dd in the background with more checks to try to prevent user error. https://help.ubuntu.com/community/mkusb & https://help.ubuntu.com/community/Installation/iso2usb – oldfred Jan 07 '21 at 03:32

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