I need to create a bootable FreeBSD install disk and the downloaded file happened to be on a Mac laptop. Since OS X is based on BSD, it also comes with dd utility.

After a USB is inserted, I need to identify the disk. This can be done using diskutil command:

$ sudo diskutil list
/dev/disk0 (internal):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                         251.0 GB   disk0
   1:                        EFI EFI                     314.6 MB   disk0s1
   2:                 Apple_APFS Container disk1         250.7 GB   disk0s2
/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +250.7 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD            98.6 GB    disk1s1
   2:                APFS Volume Preboot                 21.4 MB    disk1s2
   3:                APFS Volume Recovery                509.8 MB   disk1s3
   4:                APFS Volume VM                      3.2 GB     disk1s4
/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     Apple_partition_scheme                        *2.1 GB     disk2
   1:        Apple_partition_map                         4.1 KB     disk2s1
   2:                  Apple_HFS                         2.4 MB     disk2s2

From the above output, the USB drive is /dev/disk2. Now, I can use dd to copy the image file to the USB drive using the following command:

$ sudo dd if=FreeBSD-12.0-CURRENT-amd64-20180208-r329009-memstick.img of=/dev/disk2 bs=4m 
215+1 records in
215+1 records out
903651840 bytes transferred in 669.146642 secs (1350454 bytes/sec)

That’s it!