mac 下面用dd 制作u盘启动

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

接下来将U盘unmount

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