需要用到 hdiutil、diskutil、dd 等命令，假如 /dev/disk5 为目标u盘
cd Downloads/ hdiutil convert -format UDRW -o ubuntu.dmg ubuntu-18.04.2-desktop-amd64.iso diskutil list diskutil umountDisk /dev/disk5 mv ubuntu.dmg ubuntu.iso sudo dd if=./ubuntu.iso of=/dev/disk5 bs=1m
漫长等待，然后完成了～
1904+0 records in 1904+0 records out 1996488704 bytes transferred in 124.641015 secs (16017911 bytes/sec)