Partition the USB drive#
Identify which external USB drive you intend to use - for this post, I’ll assume it’s called /dev/sda - but make sure you’ve selected the right one. You can check the drives you have with:
sudo fdisk -l
Using cfdisk, partition the drive:
sudo cfdisk /dev/sda
Create a 6GB partition /dev/sda1 - just larger than the Ubuntu ISO, which is 5.7GB for Ubuntu 24.04. Mark the partition type as Linux filesystem.
Create a second partition /dev/sda2 in the remaining space. Mark the partition type as Microsoft basic data - this is crucial. While macOS can read/write an ExFAT partition, macOS can’t mount the partition unless it’s marked as Microsoft basic data.
Write Ubuntu ISO to drive#
Write the Ubuntu ISO using dd to the 6GB partition we created (/dev/sda1):
sudo dd bs=4M if=~/iso/ubuntu-24.04-desktop-amd64.iso of=/dev/sda1
Boot into Ubuntu live disk#
Once booted into the live disk, pull up the terminal, update ubuntu’s repos, then install exfat-fuse:
sudo apt update
sudo apt install exfat-fuse
Format the data partition as exfat#
Technically you could have formatted the /dev/sda2 partition as exfat after initially creating the partition, but I did it from within the Ubuntu live session because - in the particular situation I was faced with - I could not install the exfat package on an old machine where aptitude was severely broken, and didn’t have access to another Linux machine at the time (though had access to a Mac).
Now you can format the data partition with mkfs.exfat:
sudo mkfs.exfat /dev/sda2
Once this is done, you’ll be able to mount the partition /dev/sda2 and read from and write to it right from within the Ubuntu live session, which is running from the same drive, from the ISO image that you initially wrote to /dev/sda1. Whatever you save on /dev/sda2 will be persisted and can be read from any other OS - including other Linux distros, macOS and Windows - as they all support the ExFAT format.