Installing Windows 10 through Ubuntu Linux 20.04 without usb stick

Hi, I'm helping my friend installing W10 on his new device, thing is, neither of us have a usb drive of large enough size.
So, I'm under the impression that it is possible to install W10 if you boot into a partition which contains the ISO image.

I have some Ubuntu usbs (all 4GB so not large enough) So we installed this to his PC in the hope that we can install W10 through this. (We could go and get an 8GB USB but ideally W10 is needed ASAP.)

We've made a partition formatted with NTFS and it contains a windows 10 ISO that we downloaded. Is there anything we need to do to make this work (To boot to it and install W10)? We gave the partition the "boot" flag.

Unreleated but still an issue, since i've also tried this with a non-windows ISO lying around, the partition that we made isn't showing up in the Linux bootloader, GRUB, so I don't really know how to boot to it.

It could be somewhat unusual to install Windows 10 through Ubuntu.
A user would usually Create Bootable USB Flash Drive to Install Windows 10

arlodog said:

(We could go and get an 8GB USB but ideally W10 is needed ASAP.)

You have to get 8 GB ASAP.

Yes, you can easily install Windows from a hard drive partition. Since you formatted the partition as NTFS, and set the "boot" flag, which means make it active, it is apparent that the drive is MBR and you will most likely need to boot the computer in CSM mode (if it is a UEFI computer). Once the computer boots from the Windows setup partition, you will want to delete all partitions on the drive EXCEPT for your partition containing the setup files. Windows 10 should then set up the remaining space on the hard drive for Windows.

HOWEVER, at the end you will end up with a dual boot menu containing entries for Windows setup and for the newly installed Windows and the partition you created with the setup files will end up becoming the system partition. The way to fix that is to set the "boot" flag to the new partition containing C: drive and the Windows install. Then in a command prompt with admin privileges run the command:
bcdboot C:\Windows /s C: /f BIOS

After you do that and reboot, your C: drive will become the system partition and then you can do what you want to with the partition you put the setup files in originally.

For future reference, you should not have gone to the trouble of installing Linux on the hard drive, you should have just set up the Windows setup partition from a Linux Live running from the USB flash drive.

@NavyLCDR, do you mean an active NTFS partition containing a Windows ISO file is bootable?

Matthew Wai said:

@NavyLCDR, do you mean an active NTFS partition containing a Windows ISO file is bootable?

An active NTFS partition containing the files and folders extracted from the ISO file is bootable. And if you get the ISO file using the Media Creation Tool and partition the target drive as GPT with a small FAT32 partition, extract the ISO file to it, it will be bootable in UEFI mode.

If you don't have a 8G USB drive, how did get the ISO into the main drive? Did you downloaded using the live Linux?

You can do it in another way, using a Win 10 PE. My suggestion is to use Kyhi windows-10-recovery-tools
Make it EFI and legacy boot able.
On new hardware, boot the windows-10-recovery-tools as UEFI
Then using Mini tool partition, set your main drive as GPT and create a 20 G partition at the end of the drive.
Use the browser to download the Win 10 iso to that partition, mount the iso and run Setup.exe.
Install win 7 on the unallocated space at the beginning of the drive. Once installed, you can delete delete the 20 G partition.