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I was not aware of booting mode and installed ubuntu on my new x64,4 gb ram, Acer ES15 laptop in legacy mode. I read about the feature of uefi mode and would like to switch to uefi. When I boot on legacy mode, ubuntu loads up and system works fine, but when I change my bios setting to uefi it says no bootable device found. Should I install ubuntu again using uefi mode after erasing data? Will that work?.... Is there any other way to get to uefi mode or I need to format and then install ubuntu again using uefi bios mode? Please, help.

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3 Answers 3

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You can re-install Ubuntu, as Pilot6 suggests, and this may be acceptable if you haven't done much customization or created many user files in Ubuntu; however, it's pretty easy to install an EFI-mode boot loader for Linux. The two easiest methods are:

Method 1:

  1. Disable the Compatibility Support Module (CSM; aka "legacy mode" or "BIOS mode" support) in your firmware.
  2. Boot the Ubuntu installer in its "try before installing" mode.
  3. Double-check that you've booted in EFI mode by looking for a directory called /sys/firmware/efi. If it's present, you've booted in EFI mode and can continue; but if it's absent, you've booted in BIOS mode and should review your firmware settings and how you created the boot medium.
  4. Download and run the Boot Repair program, as described here.
  5. Tell Boot Repair to repair your installation.
  6. Reboot. With any luck, GRUB will appear and give you the option of booting either Windows or Ubuntu. In some rare cases, the system may boot straight to Ubuntu in EFI mode and you'll need to tweak GRUB to get Windows to appear in the GRUB menu.

Method 2:

  1. Disable the Compatibility Support Module (CSM; aka "legacy mode" or "BIOS mode" support) in your firmware. You may also need to disable Secure Boot, as described on this page of mine, at least temporarily.
  2. Download the USB flash drive or CD-R version of my rEFInd boot manager. (Download links for both are on that page.)
  3. Prepare the rEFInd boot medium.
  4. Reboot into the rEFInd boot medium.
  5. Boot to Ubuntu.
  6. In Ubuntu, install an EFI-mode boot loader. Two options are easiest:
    • You can run Boot Repair, as in steps #4 and #5 of Method 1
    • You can install the Debian package or PPA of rEFInd.
  7. Reboot. GRUB or rEFInd, whichever you specified, should come up and enable you to boot either Windows or Ubuntu.
  8. If desired, you can re-enable Secure Boot; however, if you installed rEFInd, you may need to manually configure Shim and install a MOK key, as described in the rEFInd Secure Boot documentation.

EDIT:

I thought you were dual-booting with Windows, but when I re-read your question, I didn't see this explicitly stated. If you're dual-booting with Windows, the above procedures should both work as-is. If you do not have a dual-boot with Windows, though, your computer may lack an EFI System Partition (ESP) and it may even use the Master Boot Record (MBR) partitioning system rather than the GUID Partition Table (GPT). If so, I recommend that you convert from MBR to GPT (if necessary), as described here. You will also need to create an ESP, which you can do with GParted using an emergency disk. You'll need to shrink an existing partition by about 550 MiB, create a new FAT32 partition in the freed space, and mark it ask an ESP by giving it a "boot" or "esp" flag (in GParted) or assigning it a type code of EF00 (in gdisk). Note that the MBR-to-GPT conversion will destroy the current BIOS-mode boot loader, so if something goes wrong and you have problems getting EFI-mode booting working, it will be harder to return to BIOS-mode booting.

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  • I don't have any other os right now.I am just using ubuntu and installed it on legacy mode.I would like to install it on uefi mode.So if i boot my system and select uefi mode from bios with usb containing ubuntu setup and select erase disk and re-install ubuntu ,will that work or will it create problem? I read your explanation and its difficult to understand for non-linux guy.Though thanks for your help.
    – Aman Dubey
    Commented May 9, 2017 at 14:07
  • If you're willing to re-install (and lose any customizations or files you've already created), then re-installing in EFI mode should work. Be aware you'll probably need to convert the disk from MBR to GPT form, but the installer will probably do this if you tell it to completely erase the disk and create new partitions.
    – Rod Smith
    Commented May 9, 2017 at 16:39
  • its a new laptop so i don't have any important files on my laptop.I will try re-installing on uefi mode.
    – Aman Dubey
    Commented May 9, 2017 at 18:15
  • Thank you so much! I made the mistake of installing Ubuntu in CMS while having Windows 10 in EFI mode. Following your Method 1 worked like a charm.
    – Delestro
    Commented Nov 28, 2020 at 15:15
  • @RodSmith I have only ubuntu linux installed on laptop and with full disk encryption. Will it work with full disk encryption? I have to type password before GRUB is shown. Thanks
    – piotrekkr
    Commented Jun 25, 2021 at 21:02
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It is much easier to do another clean install in UEFI mode, especially if you do not have enough skill in Linux systems.

But if you have some skill, it is not very difficult to switch to UEFI without re-install.

You will need to create a EFI partition and re-install grub using that partition. You can do it manually or using Boot Repair program.

In case you don't know how to manage partitions or re-install grub, I suggest re-install.

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    I tried erasing disk and re-installing on uefi mode,its installed successfully but when i try to restart it says no boot able device found.What to do?
    – Aman Dubey
    Commented May 10, 2017 at 9:28
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If you successfully installed a Ubuntu OS on UEFI, but then the system fails to see it as a boot(able) device, chances are your BIOS is set to Legacy BIOS mode. Depending upon the BIOS, try switching to UEFI mode (or load Windows 8/10/11 defaults, which should also switch to UEFI mode, depending upon the mfg / BIOS menu options(.

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