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Having live media that can boot both ways can be a problem when installing Ubuntu onto currently available Windows 8 computers.

In other words the key advantage to creating UEFI-only bootable USB live media is: You know that it definitely booted and installed via UEFI.

Since Valve has already been doing UEFI-only booting USB installers with their Steam OS and UNetbootin — the top voted alternative to Ubuntu's Startup Disk Creator — isn't UEFI compatible and therefore misleading, I think we should have a separate topic for creating UEFI-only bootable USB live media.

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2 Answers 2

up vote 23 down vote accepted

Overview

Creating UEFI-only booting USB live media is pretty straight forward. Just copy the files to your FAT32-formatted USB drive. That's it!

Remember that:

Table of contents

  • Copy files from the ISO method
    1. Example via terminal
    2. Example via GUI
    3. Example on Windows
  • The ISO loopback method (advanced)
    1. Creating the binary
    2. Creating the configuration file
    3. Adding persistency
    4. Checking the integrity
    5. UEFI Secure Boot

1. Copy files from the ISO method

1.1. Example via terminal

You can do something like the following if 604A-00EA is your USB drive and you already have p7zip installed:

$ 7z x ubuntu-12.04-desktop-amd64.iso -o/media/$USER/604A-00EA/

You're done if you have only one partition on this USB drive, otherwise you need to flag the partition as bootable e.g. via parted:

# parted /dev/sdX set 1 boot on

Where /dev/sdX would be your USB drive and 1 the partition number that should be used to boot.

1.2. Example via GUI

  1. Mount the .iso-file and copy the contents over to your USB drive. Press Ctrl+H in Nautilus to display and copy hidden files as well.

    nautilus showing Disk Image Mounter in context menu when .iso-file is selected

  2. Add the boot flag via GParted.

    GParted showing how to manage partition flags

1.3. Example on Windows

  1. Same as above, just copy files.
  2. Press Windows/Super+X, go to Disk Management and check if the partition is marked as active. On Windows versions prior to Windows 8, you press Windows/Super+R to open the run menu and open diskmgmt.msc, that would open Disk Management.

2. The ISO loopback method (advanced)

Instead of extracting contents from an ISO image, GRUB and GRUB2 have been able to boot from ISO images directly through a loopback device. Given that the ISO image is UEFI bootable, we can set up a USB drive containing multiple ISOs with different operating systems without creating a mess on the USB drive.

What do we need?

  • Very basic knowledge of GRUB configuration files.
  • Very basic knowledge of UEFI booting and GRUB, as we are going to generate our own GRUB bootloader image with a plenty of modules included.
  • A UEFI bootable ISO image, a FAT formatted USB drive and a machine that runs Linux.
    • No, we don't need a UEFI installation of Linux (which may be a chicken and egg situation), a traditional Linux VM like in VirtualBox is fine.

2.1. Creating the binary

On your Ubuntu machine or VM make sure the package grub-efi-amd64-bin is installed. The package may have a different name on another distribution, you can compare the file listing of the package to find the right package on your distribution.

The following command will generate the GRUB image, in this case an EFI binary that every computer with a UEFI firmware should be able to run:

grub-mkimage -o bootx64.efi -p /efi/boot -O x86_64-efi \
 fat iso9660 part_gpt part_msdos \
 normal boot linux configfile loopback chain \
 efifwsetup efi_gop efi_uga \
 ls search search_label search_fs_uuid search_fs_file \
 gfxterm gfxterm_background gfxterm_menu test all_video loadenv \
 exfat ext2 ntfs btrfs hfsplus udf

Every standard UEFI firmware should look into \EFI\BOOT\ for a file named boot{arch}.efi, so create the folders on the USB drive and copy the image we just created to this location. Other architectures instead of x64 are possible, but let's keep it simple with x64/amd64.

2.2. Creating the configuration file

A very basic example for a the grub.cfg configuration file that should be placed in the same directory as bootx64.efi would look like this:

set timeout=3
set color_highlight=black/light-magenta

menuentry 'Boot Ubuntu 14.04.2 LTS from ISO' {
        set isofile="/efi/boot/ubuntu-14.04.2-desktop-amd64.iso"
        loopback loop $isofile
        linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile noprompt noeject quiet splash persistent --
        initrd (loop)/casper/initrd.lz
}
submenu 'Useful snippets' {
    menuentry 'Ubuntu' {
            chainloader /efi/ubuntu/grubx64.efi
    }
    menuentry 'Windows' {
            chainloader /efi/Microsoft/Boot/bootmgfw.efi
    }
    menuentry 'Firmware Setup' {
            fwsetup
    }
}

The important thing is the configuration block with the title Boot Ubuntu 14.04.2 LTS from ISO. You can change the color and timeout to your preference. I chose black/light-magenta as it still looks a bit Ubuntu-ish but is easily distinguishable when chainloading other configurations. You can find more examples for other distributions in the Arch Wiki and reading the GRUB manual is really worth your time if you want to go beyond that.

Getting back to the configuration block, it should be obvious that the ISO is referenced as /efi/boot/ubuntu-14.04.2-desktop-amd64.iso, so copy your ISO to \EFI\BOOT\ and replace ubuntu-14.04.2-desktop-amd64.iso in the configuration with the actual filename of your ISO.

loopback loop $isofile is the line, that will load our ISO file to a loopback device from which we can boot the Linux kernel directly. This is possible because our EFI GRUB image includes the loopback module. (A bit of trial and error was involved in figuring out which modules are reasonable to include. You shouldn't see any error messages, it's still not perfect though.) Speaking of the kernel you can add kernel parameters like toram, parameters for different languages (example locale=de_DE bootkbd=de) and as in the example: persistent

2.3. Adding persistency

You can add a partition as described in: How do I get a live-USB to use a partition for persistence? Or you can create a casper-rw file and place it at the root of your USB drive.

dd if=/dev/zero of=casper-rw bs=1M count=4094
mkfs.ext4 -m 0 casper-rw

I haven't tested what the absolute maximum is, it should be somewhere between 4094 and 4096 MB. Use a partition if you intend to use more space. Note that every change to the (root) is a modification to the overlay filesystem, even deleting files.

2.4. Checking the integrity

You should look at answers to the following questions to verify that the Live ISO content on the USB drive is in pristine condition:

2.5. UEFI Secure Boot

Secure Boot will become mandatory with Windows 10 machines, I suggest you have a look at the Linux Foundation's PreLoader to add Secure Boot functionality to this setup. Here is some ASCII art illustrating menus of the accompanying HashTool.


Congratulations, I'd say you now mastered UEFI booting and shouldn't be afraid anymore.

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1  
let me point out (a) that all PCs shipped in the last 5 years or so have this capability; (b) that the .iso installer root then can use the full usb stick as ordinary persistent storage. (use ro mount options to protect from accidental deletion.) for modern PCs and common usage patterns, this seems like a better solution than live-usb-creator's default solution. –  user1539216 Dec 19 '14 at 6:22
1  
While using GUI method I have run into some symbolic links errors. Is this relevant? Can you please elaborate? –  VRR Apr 4 at 14:16
    
Hi, LiveWireBT! Thank you for such interesting answer!! I followed 2. The ISO loopback method (advanced) and managed to UEFI boot from usb flash drive. But, in the end of booting I got the error message: Can not mount /dev/loop2 on /cow and after pressing enter I saw a (initramfs) prompt. Can you help me with it? –  zuba Jun 25 at 15:01

Using dd worked for me, for some reason, the GUI version did not work. So, first, you might want to monitor the progess of dd

Then:

sudo dd if=path/to/image/file | pv | dd of=/dev/device_you_want_to_use

(/dev/device_you_want_to_use will typically be /dev/sdb, but check with df!)

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2  
Creating media this way does not result in UEFI-only bootable media. Emphasis is on the last paragraph of the question: "There is also one advantage to creating UEFI-only booting USB live media: You know that it definitely booted via UEFI." Having media that can boot both ways is a problem when trying to understand and setup a UEFI-bootable Ubuntu installation. –  LiveWireBT Jul 27 '14 at 21:14
    
I see. The weird thing is that this way, I was able to produce a image that booted in UEFI mode (I know that, since the laptop was set to allow only uefi boot and also because of the inital screen). The preffered answer did not work for me, the computer would just not boot with an image created by just copying the files. –  sup Jul 28 '14 at 7:32

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