1、首先下载Ubuntu系统，直接去阿里云镜像
https://developer.aliyun.com/mirror/
2、准备好U盘，先给U盘格式化，使用命令
使用如下命令列出所有磁盘，找到U盘（我的是/dev/disk3）
diskutil list
cwk@helloale ~ % 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 27.7 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 disk1s2, disk0s2
1: APFS Volume Macintosh HD - Data 364.1 GB disk2s1
2: APFS Volume Preboot 3.7 GB disk2s2
3: APFS Volume Recovery 1.2 GB disk2s3
4: APFS Volume VM 4.1 GB disk2s4
5: APFS Volume Macintosh HD 9.8 GB disk2s5
6: APFS Snapshot com.apple.os.update-... 9.8 GB disk2s5s1
/dev/disk3 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: FDisk_partition_scheme *30.8 GB disk3
1: DOS_FAT_32 UNTITLED 30.8 GB disk3s1
可以看到有三块磁盘，最后一块是我的U盘，输入下面命令格式化
diskutil partitionDisk /dev/disk3 MBR FAT32 UNTITLED 0b
cwk@helloale ~ % diskutil partitionDisk /dev/disk3 MBR FAT32 UNTITLED 0b
Started partitioning on disk3
Unmounting disk
Creating the partition map
Waiting for partitions to activate
Formatting disk3s1 as MS-DOS (FAT32) with name UNTITLED
512 bytes per physical sector
/dev/rdisk3s1: 60056896 sectors in 1876778 FAT32 clusters (16384 bytes/cluster)
bps=512 spc=32 res=32 nft=2 mid=0xf8 spt=32 hds=255 hid=2048 drv=0x80 bsec=60086272 bspf=14663 rdcl=2 infs=1 bkbs=6
Mounting disk
Finished partitioning on disk3
/dev/disk3 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: FDisk_partition_scheme *30.8 GB disk3
1: DOS_FAT_32 UNTITLED 30.8 GB disk3s1
cwk@helloale ~ %
这样U盘就格式化成FAT32格式了
3、将下载的iso系统文件刻录到U盘
首先、使用如下命令卸载U盘
diskutil umountDisk /dev/disk3
cwk@helloale ~ % diskutil umountDisk /dev/disk3
Unmount of all volumes on disk3 was successful
cwk@helloale ~ %
可以看到卸载成功了。
接下来就开始刻录、输入如下命令
sudo dd if=ISO文件路径 of=/dev/disk3 bs=10m
这里使用的命令：
sudo dd if=/Users/cwk/Desktop/ubuntu-18.04.6-live-server-amd64.iso of=/dev/disk3 bs=10m
输入密码后，耐心等待，需要一定的时间。
cwk@helloale ~ % sudo dd if=/Users/cwk/Desktop/ubuntu-18.04.6-live-server-amd64.iso of=/dev/disk3 bs=10m
96+1 records in
96+1 records out
1016070144 bytes transferred in 258.626095 secs (3928722 bytes/sec)
cwk@helloale ~ %
如上，系统盘就制作完成了。
参考文章
http://www.voycn.com/index.php/article/macxiashiyongdiskutilgeiupangeshihua
https://wangmaolin.net/topic/Mac/8loynzzyz3
说点题外话，文言一心给我的都是错误答案！
