Not sure which image?
Find my imageFour questions narrow it to one image, with its ISO, its rebase command and a custom-ISO build in the browser.
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Writing the ISO to a USB drive
These are hybrid UEFI images — write one directly to a USB stick and boot it:
sudo dd if=tunaos.iso of=/dev/sdX bs=4M status=progress oflag=directReplace /dev/sdX with your USB device (double-check with lsblk — this erases the target). On Windows or macOS, balenaEtcher works too. After booting, follow the installer guide.