Raspberry Pi INSTALLING OPERATING SYSTEM IMAGES ON MAC OS

Last login: Sun Jan 31 02:05:04 on console
XUEFEIdeMacBook-Pro:~ xuefei$ df -h
Filesystem      Size   Used  Avail Capacity  iused    ifree %iused  Mounted on
/dev/disk1     233Gi  106Gi  126Gi    46% 27826588 33160610   46%   /
devfs          184Ki  184Ki    0Bi   100%      638        0  100%   /dev
map -hosts       0Bi    0Bi    0Bi   100%        0        0  100%   /net
map auto_home    0Bi    0Bi    0Bi   100%        0        0  100%   /home
/dev/disk2s1    15Gi  2.4Mi   15Gi     1%        0        0  100%   /Volumes/RASPBIAN
XUEFEIdeMacBook-Pro:~ xuefei$ diskutil unmount /dev/disk2s1 
Volume RASPBIAN on disk2s1 unmounted
XUEFEIdeMacBook-Pro:~ xuefei$ 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_CoreStorage Macintosh HD            250.1 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.1 MB   disk0s3
/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           +249.8 GB   disk1
                                 Logical Volume on disk0s2
                                 2974E977-85C8-4CA7-B66E-20883AD07954
                                 Unlocked Encrypted
/dev/disk2 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *15.9 GB    disk2
   1:                 DOS_FAT_32 RASPBIAN                15.9 GB    disk2s1
XUEFEIdeMacBook-Pro:~ xuefei$ dd bs=1m if=raspbian.img of=/dev/rdisk2
rdisk2    rdisk2s1  
XUEFEIdeMacBook-Pro:~ xuefei$ dd bs=1m if=raspbian.img of=/dev/rdisk2
rdisk2    rdisk2s1  
XUEFEIdeMacBook-Pro:~ xuefei$ dd bs=1m if=raspbian.img of=/dev/rdisk2
dd: /dev/rdisk2: Permission denied
XUEFEIdeMacBook-Pro:~ xuefei$ dd bs=1m if=raspbian.img of=/dev/disk2
dd: /dev/disk2: Permission denied
XUEFEIdeMacBook-Pro:~ xuefei$ sudo dd bs=1m if=raspbian.img of=/dev/rdisk2
Password: 

3752+0 records in
3752+0 records out
3934257152 bytes transferred in 195.376528 secs (20136795 bytes/sec)
XUEFEIdeMacBook-Pro:~ xuefei$ xuefei