A usb drive with only 1 partition to load grub2 on usb-bootable machines with Legacy BIOS, 64bit UEFI or 32bit UEFI.
Note: due to the maximum size of a file inside an EFI system partition, files (such as ISO disk images) of 4 GiB or larger must be placed on another partition. That second partition can be of type ext4, for instance.
Partition the drive and install grub2
Warning: the usb drive will be formatted, save your data before proceeding!
First of all, on you current installation, check if the folder /usr/lib/grub/ exists and is not empty. If it is empty or does not exist, make sure the package grub-common (or equivalent for your distribution) version 2 or higher is installed. Depending on the system, /usr/lib/grub/ will contain one or more of the following folders: x86_64-efi, x86_64-efi-signed, i386-pc, i386-efi, …
The x86_64-efi, i386-pc and i386-efi folders need to be present in order to install the corresponding bootloader on the usb drive.
Install them using the package manager, for instance on Ubuntu :
sudo apt install grub-pc-bin grub-efi-ia32-bin grub-efi-amd64-bin
Now, find the device file for your usb drive. Here, the file is /dev/sdX. Replace X with the appropriate lower case letter(s) in the commands.
Make sure it’s the right drive! (check the capacity and the partitions) :
sudo fdisk -l /dev/sdX
Open fdisk :
sudo fdisk /dev/sdX
Press the following keys (THIS WILL ERASE ALL DATA FROM THE SELECTED DRIVE!) :
o <enter> # Create a new empty DOS partition table
n <enter> # Create a new partition
p <enter> # Select primary partition type
1 <enter> # Set partition number to 1
<enter> # Start partition at the first possible sector (default)
<enter> # Set partition end to the last possible sector (default)
Note: if fdisk (newer versions only) asks whether the partition signature should be deleted, then answer yes.
t <enter> # Change partition type
e f <enter> # Set partition type to EFI (FAT-12/16/32)
a <enter> # Enable the bootable flag on partition 1
w <enter> # Write the partition table
Create a fresh filesystem in the newly created partition :
sudo mkfs.fat -F32 /dev/sdX1
Mount the filesystem :
sudo mount -o umask=000 /dev/sdX1 /mnt
Write the MBR and install the grub files required for legacy BIOS boot on the drive :
sudo grub-install --no-floppy --boot-directory=/mnt/boot --target=i386-pc /dev/sdX
Install /EFI/BOOT/BOOTX64.EFI and other grub files required to load grub from a 64-bit UEFI firmware :
sudo grub-install --removable --boot-directory=/mnt/boot --efi-directory=/mnt --target=x86_64-efi /dev/sdX
Install /EFI/BOOT/BOOTIA32.EFI and other grub files required for 32-bit UEFI :
sudo grub-install --removable --boot-directory=/mnt/boot --efi-directory=/mnt --target=i386-efi /dev/sdX
Create a grub.cfg file :
touch /mnt/boot/grub/grub.cfg
Example grub.cfg with Xubuntu 22.04 Live
Notes :
- Skip this part if you already have a working grub.cfg for the usb drive.
- Other examples can be found in this repository’s grub.cfg file.
Create a folder for cd images :
mkdir /mnt/isos
Download an Ubuntu CD image (for example: Xubuntu 22.04 64-bit) :
Note: make sure there is enough space on the usb drive.
wget --directory-prefix=/mnt/isos http://cdimages.ubuntu.com/xubuntu/releases/jammy/release/xubuntu-22.04.3-desktop-amd64.iso
Edit grub.cfg :
nano /mnt/boot/grub/grub.cfg
Write or paste something like this :
menuentry 'Xubuntu 22.04 amd64' {
#rmmod tpm #uncomment if grub version is >=2.04 in UEFI mode (see https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1851311)
set isofile="/isos/xubuntu-22.04.3-desktop-amd64.iso"
#search --set=root --file $isofile #uncomment if the bootloader and OS files are on different partitions
loopback isoloop $isofile
linux (isoloop)/casper/vmlinuz locale=fr_FR console-setup/layoutcode=fr boot=casper iso-scan/filename=$isofile quiet --
initrd (isoloop)/casper/initrd
}