date; sudo dd bs=1M if=2020-02-13-raspbian-buster-full.img of=/dev/rdisk3; date
    Thu Apr 23 20:22:45 PDT 2020
    dd: failed to open '/dev/rdisk3': Permission denied
    Thu Apr 23 20:22:54 PDT 2020

I've tried giving Full Disk Access to all of these, but to no avail:


enter image description here

The device exists:

diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk1         1.0 TB     disk0s2

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +1.0 TB     disk1
                                 Physical Store disk0s2
   1:                APFS Volume d - Data                638.3 GB   disk1s1
   2:                APFS Volume Preboot                 81.1 MB    disk1s2
   3:                APFS Volume Recovery                526.9 MB   disk1s3
   4:                APFS Volume VM                      3.2 GB     disk1s4
   5:                APFS Volume d                       11.1 GB    disk1s5

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *8.0 TB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS time-machine2           2.0 TB     disk2s2
   3:                  Apple_HFS data2                   6.0 TB     disk2s3

/dev/disk3 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *31.9 GB    disk3
   1:             Windows_FAT_32 NO NAME                 31.9 GB    disk3s1

I'm not sure what the problem is?

  • 1
    Can you write to the disk using Etcher? balena.io/etcher – Bert Apr 24 '20 at 12:11
  • @Bert: Etcher showed /dev/disk3 as being "Locked". In this particular case, the Lock switch on the SD card was in the down position which prevented writing. – Alex Ryan Apr 24 '20 at 16:17

My bad. If this happens to you, you might want to check the switch on your SD card to see if it is set to read-only. :)

  • 1
    Haha it happens to the best of us. I'm glad you kept this question up and posted this answer, it'll undoubtedly serve as a helpful reminders to many others in the future :) – Alexander Apr 24 '20 at 17:48
  • 1
    note the command that failed had /dev/rdisk3 in the argument, while diskutil shows /dev/disk3 (no "r") – Efren May 5 '20 at 2:08

Catalina mounts system directory's in apfs containers (think linux lvm volume) explicitly as read-only, yet another security feature.

To access raw block devices you need to remount with explicitly adding rw options: bsd mount: mount -uw / or mount -X /, try to add -o remount I think, look at man mount and diskutil help I don't recall bsd mount opts now exactly but starting macOS in single mode will give you a warning about read-only and how to remount in rw, so try booting holding cmd - s and take a look what it says, type exit to start launched default session ergo normal start.

using gnu mount: mount /dev/diskXsX -o remount,rw,force

What does df -H and mount shows in terminal? Check if mount points are flagged as ro only.

Update: disable this "feature" (SIP) in recovery mode: csrutil enable --without fs , then you can remount with rw access without disabling SIP completely - although I always disable all SIP stuff including gatekeeper sudo spctl --master-disable but it's not recommended by apple 😀


Most probably you are using an SD card adapter. Many are defective. The best solution: use a micro SD to USB adaptor (1€ on eBay) it has no switch, it will work.

Before that try to touch the switch or reinsert, it might work.

This is bad quality contacts, even if the micro SD itself is good.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .