HOWTO convert ubuntu 18.04 LTS ISO to bootable USB installation disk on Mac OSX

minimum 2GB size of SD card

0) find name of SD card in file system

diskutil list

1) download from ubuntu.com the 18.04 LTS image

cd ~/Downloads/

ls ubuntu-18.04-desktop-amd64.iso

2) convert ISO to dd-table binary image

hdiutil convert -format UDRW -o ubuntu1804.img ubuntu-18.04-desktop-amd64.iso

3) unmount SD card, eg. disk3

diskutil unmountDisk /dev/disk3

4) write to SD card

sudo dd if=./target.img.dmg of=/dev/rdisk3 bs=1m