1st set of commands

Using these commands with GDISK:

> sudo gdisk /dev/sdb

I get:

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING PARTITIONS!!

Do you want to proceed? (Y/N): Y

OK; writing new GUID partition table (GPT) to /dev/sdb.

Unable to open device '/dev/sdb' for writing! Errno is 30! Aborting write!

2nd set of commands

Also using another set of GDISK commands:

> sudo gdisk /dev/sdb

I get:

About to wipe out GPT on /dev/sdb. Proceed? (Y/N): Y

Problem opening '/dev/sdb' for writing! Program will now terminate.

Blank out MBR? (Y/N): Y

Warning! MBR not overwritten! Error is 30!


The device is a flash USB drive.

  • What might be the cause?
  • What else can I try?


The dd couldn't help:

> sudo dd if=/dev/zero of=/dev/sdb status=progress
dd: failed to open '/dev/sdb': Read-only file system


FDISK didn't help too:

> sudo fdisk /dev/sdb

Welcome to fdisk (util-linux 2.33.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

fdisk: cannot open /dev/sdb: Read-only file system


I had already used hdparm:

> sudo hdparm -r0 /dev/sdb

 setting readonly to 0 (off)
 readonly      =  0 (off)


I'm able to see USB drive content by a MacBook! So, the hardware is fine. macOS reports the filesystem as MS-DOS (FAT32).

macOS Disk Utility

Trying to format the device with macOS Disk Utility throws these error:

When erasing partition:

Starting secure erase…

Unmounting disk

Creating the partition map

Couldn’t open device.

Operation failed…

When erasing filesystem:

Unmounting disk

Couldn’t modify partition map.

Operation failed…

Wipefs tool

Wipefs tool output:

> sudo wipefs -a /dev/sdb
wipefs: error: /dev/sdb: probing initialization failed: Read-only file system
  • 2
    Is there anything relevant in the kernel messages? Have you tried a different command, such as parted or fdisk? I don't know if there is anything on the drive you want to keep, but if not, try writing to it with another tool like dd. Apr 30, 2021 at 14:19
  • @berndbausch Thanks =) Updated the post :)
    – Megidd
    Apr 30, 2021 at 14:26
  • Disks cannot be mounted while you alter partitions on the disk. Read man umount.
    – waltinator
    Apr 30, 2021 at 14:47
  • 1
    Something makes the drive readonly. See superuser.com/questions/1125282/… and other articles in Stackexchange and the internet. You could try it on a different computer, e.g. one running Windows. Or simply buy another drive. May 1, 2021 at 2:10
  • Please try sudo touch /dev/wibble (or any other filename in /dev that does not exist). If you get a Read-only file system error the problem is nothing to do with /dev/sdb but rather something's gone wrong with the /dev subsystem May 1, 2021 at 12:09

1 Answer 1


The device make and model is

SanDisk Ultra Media USB External Physical Disk 

According to this:

Is this a sandisk usb? Some have a hardware 'safety lock' that locks the usb to read-only in the event of a usb power fluctuation. I had one that did this and had to be returned, though they replaced it FOC.

According to that:

According to SanDisk customer service, those drives have a safety mechanism that disables writes when error conditions are detected, to protect the data:

The flash drive has detected a potential fault and has become write protected to prevent data loss. There is no method to fix this. You will need to backup your data and replace the flash drive.

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