So I got a used Laptop a month ago an planned to set it up for my own use. I wanted to set up Windows 10 and Ubuntu on it but have not been able to do so. I would be mention below what I have tried so far. Please take a look and see if I am doing something wrong.

  1. I turned off Secure Boot (So that I could boot from USB).

  2. Set boot mode to UEFI and Legacy from the default UEFI OS. The Third option was CSM OS.(God knows what it is).

  3. Booted my laptop into windows 10 setup on the usb, deleted all previous partitions, created a new partition for the windows leaving more than half unallocated for the ubuntu installation and finally got done with a clean windows installation.

  4. Then I booted my laptop on the Ubuntu setup on usb and launched the installation. For some reason the Ubuntu setup failed to detect existing operating system on the disk and hence did not show me the "install alongside" option. This is where I am stuck. I have tried different ways to proceed from here by going into "something else" option but all my efforts have been wasteful.

In fact I lost windows 10 a couple of times so had to repeat step 3. Perhaps got my boot loader corrupt.

What I understand is the Ubuntu setup must be aware of the existing OS on the machine and something is not letting it to do so. In the "something else" option the only partition I see is my full hard disk as a whole in free space.

Kindly help me with it.


This sounds like the typical issue of mixing boot modes.

Ensure that everything is setup and boots in the mode you want to install either UEFI or legacy. Disable or deprecate the other method during system installation (e.g. remove MBR loaders from installation media) so that you can rule out any confusion about that.

Related question: "Install alongside" option missing. How do I install Ubuntu beside Windows using "Something Else"?

  • I have already looked at that. Could not help myself. – Muhammad Ali Oct 4 '15 at 6:51

To elaborate on LiveWireBT's answer, enabling the Compatibility Support Module (CSM) greatly complicated your boot path and makes it impossible, from your description, to determine whether your re-installed Windows is installed in EFI/UEFI mode or in BIOS/CSM/legacy mode. If the latter, Windows will have incompletely converted the partition table from GPT to MBR form, which would confuse the Ubuntu installer, making the disk appear to be empty. Just as bad, the Ubuntu installer could end up booting in EFI mode, which could result in a mixed-mode OS installation (Windows in BIOS mode, Ubuntu in EFI mode). For more on the perils of the CSM, see my page on the subject.

As you might gather from the preceding, enabling the CSM/legacy support in your firmware was a mistake. If you can force the computer to boot in this mode, it's not so bad -- you can clean up the leftover GPT data with my FixParts, which is included in the gdisk package in Ubuntu, and proceed with your installation. Most computers, though, don't let you completely disable EFI-mode booting; even setting the firmware to "legacy support" just makes the CSM available; the computer might still choose to boot in EFI mode, and there's usually no clear indicator that you've booted in this mode rather than in BIOS mode.

Thus, the better course of action, IMHO, is to start over again: Disable the CSM in your firmware, re-install Windows in EFI mode, and then install Ubuntu in EFI mode. With the CSM disabled, there will be little or no chance of your booting in BIOS mode. (Theoretically there'll be no chance, but there's always the possibility that your firmware will still give itself the option of booting in BIOS mode, or you might miss something in the firmware setup utility, in which case all bets are off.)

Note, however, that the "install alongside" option is usually missing from modern Windows installations to GPT disks. You may need to use the "something else" option to manually partition your disk.

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