#Convert ISO file to DMG file
hdiutil convert -format UDRW -o CentOS-7-x86_64-Minimal-2003.dmg CentOS-7-x86_64-Minimal-2003.iso
#View storage device list
diskutil list
#Cancel the mounting of U disk
diskutil unmountDisk /dev/disk2
#Make U disk installation disk
sudo dd if=CentOS-7-x86_64-Minimal-2003.dmg of=/dev/disk2