# 1. List mounted drives
lsblk

# 2. Unmount the drive if mounted
sudo umount /dev/sda1

# 3. Write ISO into drive (takes a while)
sudo dd bs=4M if=path/to/ubuntu.iso of=/dev/sdX conv=fdatasync status=progress

# 4. Sync the file system
sync

# 5. Eject USB
sudo eject sda1