用dd来把安装包烧到U盘的，发现U盘变小了，mac磁盘工具也不能格式化，就只好用命令行了。
diskutil list #1.找到U盘的代号 比如disk1
diskutil unmountDisk /dev/disk1 #2.
diskutil eraseDisk JHFS+ iDisk disk1 #3.
Downloads diskutil list /dev/disk0 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *28.0 GB disk0 1: EFI EFI 314.6 MB disk0s1 2: Apple_APFS Container disk2 27.6 GB disk0s2 /dev/disk1 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *1.0 TB disk1 1: EFI EFI 209.7 MB disk1s1 2: Apple_APFS Container disk2 1000.0 GB disk1s2 /dev/disk2 (synthesized): #: TYPE NAME SIZE IDENTIFIER 0: APFS Container Scheme - +1.0 TB disk2 Physical Stores disk0s2, disk1s2 1: APFS Volume Macintosh HD - Data 227.8 GB disk2s1 2: APFS Volume Preboot 81.9 MB disk2s2 3: APFS Volume Recovery 528.9 MB disk2s3 4: APFS Volume VM 8.6 GB disk2s4 5: APFS Volume Macintosh HD 10.6 GB disk2s5 ? Downloads diskutil list /dev/disk0 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *28.0 GB disk0 1: EFI EFI 314.6 MB disk0s1 2: Apple_APFS Container disk2 27.6 GB disk0s2 /dev/disk1 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *1.0 TB disk1 1: EFI EFI 209.7 MB disk1s1 2: Apple_APFS Container disk2 1000.0 GB disk1s2 /dev/disk2 (synthesized): #: TYPE NAME SIZE IDENTIFIER 0: APFS Container Scheme - +1.0 TB disk2 Physical Stores disk0s2, disk1s2 1: APFS Volume Macintosh HD - Data 227.8 GB disk2s1 2: APFS Volume Preboot 81.9 MB disk2s2 3: APFS Volume Recovery 528.9 MB disk2s3 4: APFS Volume VM 8.6 GB disk2s4 5: APFS Volume Macintosh HD 10.6 GB disk2s5 /dev/disk3 (external, physical): #: TYPE NAME SIZE IDENTIFIER 0: Apple_partition_scheme *8.1 GB disk3 1: Apple_partition_map 4.1 KB disk3s1 2: Apple_HFS 2.5 MB disk3s2 ? Downloads diskutil unmountDisk /dev/disk3 Unmount of all volumes on disk3 was successful ? Downloads diskutil eraseDisk JHFS+ iDisk disk3 Started erase on disk3 Unmounting disk Creating the partition map Waiting for partitions to activate Formatting disk3s2 as Mac OS Extended (Journaled) with name iDisk Initialized /dev/rdisk3s2 as a 7 GB case-insensitive HFS Plus volume with a 8192k journal Mounting disk Finished erase on disk3
diskutil unmountDisk /dev/disk3
sudo dd bs=10m if=./ubuntu-19.10-beta-desktop-amd64.iso of=/dev/rdisk3 #烧制U盘
diskutil eject /dev/disk1
查看进度
sudo pkill -INFO dd # mac系统原文：https://www.cnblogs.com/jackluo/p/11685076.html