grub-install: error: cannot find EFI directory.

[satish mali]

I have windows 10 installed on my computer.
I have single disk of 500gb size ( 1 partition - 50mb - system required - NTFS, 2nd partition 165 gb - primary - wherein windows 10 installed).
I tried to install Ubuntu as secondary OS in dual boot format.
at the end of installation, it gave error as fatal error.

Please help us to understand the steps needed while installing ubuntu as dual boot os.
I would like to know whether a new separate EFI boot partition is needed for ubuntu?

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: ubiquity 20.10.13
ProcVersionSignature: Ubuntu 5.8.0-25.26-generic 5.8.14
Uname: Linux 5.8.0-25-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu50
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.455
CurrentDesktop: ubuntu:GNOME
Date: Mon Nov 30 18:10:04 2020
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 20.10 "Groovy Gorilla" - Release amd64 (20201022)
ProcEnviron:
 LANGUAGE=en_IN
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_IN
 LC_NUMERIC=C.UTF-8
RebootRequiredPkgs:
 linux-image-5.8.0-25-generic
 linux-base
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[oldfred (oldfred)]

Windows requires MBR(msdos) partitioning for BIOS boot.
Ubuntu will let you install in UEFI mode to MBR drive, but probably should not as Windows wants boot partition to be its partition with boot files (system), but UEFI wants boot flag on ESP - efi system partition.
UEFI highly recommends gpt partitioning for UEFI, and Windows only installs in UEFI mode to gpt drives. Normal reinstall in different mode will erase drive. So if you attempt to reinstall Windows in UEFI mode, it will convert drive to gpt & totally erase drive. Or have good backups.

Either reinstall Windows in UEFI mode since you have UEFI hardware. Microsoft has required vendors to install in UEFI mode to gpt partitioned drives since 2012 and release of Windows 8.

Or only install Ubuntu in 40 year old BIOS/MBR configuration.

How you boot install media, UEFI or BIOS is then how it installs.