I have a macbook pro running Snow Leopard. I have Tuxera NTFS drivers.

I have a microSD card, in an adapter, in the slot. The "lock" slider is in the "unlocked" position.

'Get Info' tells me the drive is formatted to FAT16. The permissions panel tells me that I can only read.

Disk utility tells me it's not writable. (It does this for the volume and also for the higher level Apple SD Card Reader Media)

What do I need to do to change permissions to turn this card writable?

  • format it as Fat32 – Jason Dec 4 '12 at 23:47
  • @Jason - I can't format it. Disk Utility can't write to it, thus can't format it. – DanBeale Dec 4 '12 at 23:59
  • Is it a microSD card sold as rewritable media? This is expected behavior for read-only cards that might only be used for specialized purposes. Corollary: can you write to the card from a Windows computer? NTFS drivers shouldn't be necessary -- FAT16 can be natively written to in Mac OS X. – NReilingh Dec 5 '12 at 0:25
  • It is a card sold as re-writeable media. It has, previously, been written on. FAT16 can be natively written to by OS X - but nothing is allowing me to write anything to this card, even though it is currently FAT16. – DanBeale Dec 10 '12 at 13:32

I've encountered the same. Ended up doing this:

  1. Backup the SD Contents
  2. Format the SD as FAT16 using Disk Utility and Terminal

following these steps:

  1. Unmount (not eject) the SD from Disk Utility and copy the id (doing CMD+I on the SD and then selecting the Disk Identifier value (e.g. disk2s1))
  2. Format to FAT16: sudo newfs_msdos -F 16 /DEV_PATH/TO_SDK so in my case: sudo newfs_msdos -F 16 /dev/disk2s1


  • 2
    I got "permission denied". – Whit May 22 '16 at 21:59
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    @Whit If you're using a microSD to SD card adapter, double check the notch on the side of the card that locks writing (that got me a while back)...make sure its in a position that doesn't lock writing :) – George Profenza May 22 '16 at 22:31
  • Turns out it was a bad adapter. Canakit mailed me a new one and bingo. :) – Whit Jun 5 '16 at 20:06
  • ouch! frustrating to find out it's not something commonly expected to fail, glad that got sorted out in the end :) – George Profenza Jun 5 '16 at 20:07
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    @GeorgeProfenza I spent 45 minutes in bash before I saw this comment and remembered that exists. [facepalm] – Kevin Suttle Jul 7 '17 at 14:40

I had a PNY 32gb SD Card. Spent hours trying to find out how to make it re-writeable. Well the answer is simple. The slider on the left side of the card must be "up" (the read-writable position) BUT ALSO the tiny "notch" opposite the slider must be covered with a piece of tape. It's really the opposite of the old video tapes, which we had to break the tab if we did not want anything recorded over it. But I can guarantee you I've bought a lot of SD cards and have NEVER had a card that was write-protected out of the package that required me to do anything but raise the slider on the left side.

  • 1
    I saw this too, can anyone explain this insanity? It's just a notch in the plastic. – oarfish Nov 15 '17 at 8:57

Had the same problem, I unmounted it using terminal, following this tutorial


  • 2
    While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. – grg Apr 15 '15 at 17:59

I had no clue why my sd card somehow got turned onto unwritable. I filled it up to 8/ 16 gigs n decided, OK I really need to fix this card now!

I finally recalled some cards can lock data. After a few flips n tests with the switch slides. I'm not finnaly able to delete again.

So simple. Built in lock mechanism on the actual card!

I tried reformating, no availablity, moving from card to desktop, changing options in each folder. But it was there the whole time.

  • 2
    The question-asked clearly states the physical lock switch on the card is in the "unlocked" position. You may wish to delete this answer as it will continue to attract down votes for not actually addressing the question being asked. For more information on how Ask Different and the StackExchange Q&A format works please see our FAQ. – Ian C. Jul 8 '15 at 3:02

Switch the lock mechanism on the physical SD card.

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    Welcome to Ask Different. It's helpful if you read the whole question being asked and not just the title; in this case the second line tells us what we need to know. I suggest taking some time to take the Tour – Allan Jan 12 '17 at 22:34

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