Copying an operating system image to an SD card using Mac OS

First,verify the path to your SD card.You can do this by runing the following command from terminal:

diskutil list

In this case i can verify /dev/disk2 is my SD card because the TYPE,NAME and Size values are correct.

IF you have an existing partiton on the disk you may need to unmount it,otherwise you'will get a ''Resource Busy" error message when you try to write the image .

diskutil unmount /dev/disk2s1

Now to write the image file to the disk. Note the 'r' added to rdisk2 which drastically improves write performance by telling dd to operate in raw disk mode:

sudo dd if=2019-09-26-raspbian-buster.img of=/dev/rdisk2 bs=1m

Depending on the size of your SDcard this may take a while. You can press CTRL+T to see the current status of dd. 

Copy the image

• From Terminal, enter:

  sudo dd bs=1m if=path_of_your_image.img of=/dev/rdiskN conv=sync

  Replace N with the number that you noted before.

  This can take more than 15 minutes, depending on the image file size. Check the progress by pressing Ctrl+T.

  If the command reports dd: bs: illegal numeric value, change the block size bs=1m to bs=1M.

  If the command reports dd: /dev/rdisk2: Operation not permitted you need to disable SIP before continuing.

  If the command reports the error dd: /dev/rdisk3: Permission denied, the partition table of the SD card is being protected against being overwritten by Mac OS. Erase the SD card's partition table using this command:

  sudo diskutil partitionDisk /dev/diskN 1 MBR "Free Space" "%noformat%" 100%

  That command will also set the permissions on the device to allow writing. Now issue the dd command again.

After the dd command finishes, eject the card:

sudo diskutil eject /dev/rdiskN

来源：oschina

链接：https://my.oschina.net/u/3378766/blog/3159854