I have used dd because it is what the tutorials suggest to do for instance when copying Linux images to SD cards (e.g. Raspbian, Kali, ...). This is done at 1 Mb/sec on my macbook pro. I have tried to change the bs option of dd, e.g. bs=1m or bs=10m or bs=100m but copying a 32 Gb image takes hours and the rate is always around 1 Mb/s.

I read on linux some users suggest to use cat instead of dd . This seems to not work for me as even with sudo I get an error for insufficient permissions.

Just to be clear, the disk partitions are unmounted via

sudo diskutil unmount /dev/disk2
sudo diskutil unmountDisk /dev/disk2

Also, I should have specified that dd works where cat is blocked by the permission error.

So my question is, what is the quick and reliable way to copy OS images of tens of Gbytes to a SD card in OS X?

  • How is the SD Card reader connected to your Mac? – nohillside Jul 21 '20 at 11:41
  • make sure the SD Card Volume is unmounted before attempting to use Terminal Commands like cat or dd – Matthew Barclay Jul 21 '20 at 13:14
  • I should have specified that dd works where cat is blocked by the permission error. The card is connected via USB-C card reader and with Balana Etcher suggested by @Tony Williams it can be written at 15+ Mb/sec – Rho Phi Jul 21 '20 at 15:45
  • How were you using cat? If you used something like sudo cat someimage.iso >/dev/disk2, the problem is that the redirect is done by the shell, without privilege. See the Unix&Linux question "Redirecting stdout to a file you don't have write permission on" and its answers. – Gordon Davisson Jul 21 '20 at 19:07
  • You got me! I was doing that redirect! – Rho Phi Jul 22 '20 at 14:19

I use Balana Etcher for my Raspberry Pi SD cards. It's free, fast and even verifies. It's also cross platform.

  • This is going so much faster! 20 Mb/sec! Do I understand correctly that it does the job only one way: from file to SD card and not the vice-versa? – Rho Phi Jul 21 '20 at 15:42
  • To be honest I've never tried the other way, but I think it only does onto the SD card. Oh, if you think my solution is your answer you should mark it correct. – Tony Williams Jul 22 '20 at 6:03
  • I would, it that would replace entirely dd, but I am afraid it does not because I do not see how Etcher can write from the SD to a file. I am trying Disk Utility right now but it does not react to File> New Image>Image From "diskname". I have tried to unmount the partition using the GUI of Disk Utility but seems to make no difference. – Rho Phi Jul 22 '20 at 8:49

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