U盘变小了怎么办

打开 terminal

查看U盘识别的磁盘号:

leo@leodeMacBook-Pro  ~/Downloads  diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk1         250.8 GB   disk0s2

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +250.8 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD            227.9 GB   disk1s1
   2:                APFS Volume Preboot                 44.9 MB    disk1s2
   3:                APFS Volume Recovery                510.3 MB   disk1s3
   4:                APFS Volume VM                      5.4 GB     disk1s4

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     Apple_partition_scheme                        *31.2 GB    disk2
   1:        Apple_partition_map                         4.1 KB     disk2s1
   2:                  Apple_HFS                         2.5 MB     disk2s2

完全擦除设备:

diskutil eraseDisk free EMPTY /dev/disk2

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