Read-only SD cards

Question

I've got an IcyBox USB hub/card reader combo in my computer, running Ubuntu 12.10.

It's got an issue with SD cards. It always mounts them read-only, regardless of the write-lock switch. This is observed across many SD cards that otherwise work, and crucially occurs for a microSD in an adapter, where the microSD was fine in the microSD slot in the reader.

Anyone got any ideas as to what's going on and how I can fix it?

Solution 1

It sounds to me to be a permissions issue. I've come across this myself with my Linux Mint 14 (Cinnamon) install, which I believe is based on Ubuntu 12.10.

First thing to do is to check the permissions on the hardware device mounting your card. You'll need to find the device name. To do this run the following command:

sudo fdisk -l

Your device will probably be something along the lines of /dev/sdb1, in my case the SD Reader was /dev/mmcblk0p1.

Next you need to get the permissions on this device:

sudo ls -l /dev/mmcblk0p1

Replace "/dev/mmcblk0p1" with your device location. The output will look something like this:

brw-rw---- 1 root disk 179, 1 Feb 3 21:58 /dev/mmcblk0p1

This tells us the device is owned by User 'root' and group 'disk' You need to be a member of group 'disk' to be able to write to the SD card. You can check which groups your a member of with

groups username

In my case I was not a member of the 'disk' group, I rectified this with

sudo usermod -G disk --append username

This adds the group 'disk' to your user's groups, which should allow you to now read & write to the SD card

Solution 2

USE:

dosfsck -l -t /dev/sdb

Remove dirty bit (y) Answer Yes for ALL

Solution 3

In my case Ubuntu auto-mounted the SD Card into a directory it created that didn't have write permissions.

• Once mounted (accessible but read-only), find the mount point: /media/{username}/{sd-card name}

  (in my case this was: /media/andrew/SDCard - you can find this by right-clicking on the drive, selecting 'Properties' and looking for 'Mounted on', or by typing mount -l in a terminal)

• Open a terminal and type the following: sudo chmod 777 /media/{username}/{sd-card name}

  e.g. sudo chmod 777 /media/andrew/SDCard

The SD card is now writable

Solution 4

Get hold of a PC running windows, download a program called SD Formatting, install and reformat the SD card, making sure the option is set to "ON", it will then be recognised on a Linux machine! without the read only option.

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Comments

[matt]

"sudo usermod -G disk username" removed my other groups from my account. Adding "--append" will add the group without removing the existing groups.

[Cédric Girard]

--append must be after the group name, like sudo usermod -G disk --append username (else there is an error about group "--append")

[Celio Marcos]

with this command the result is: cannot remount /dev/sdc1 read-write, is write-protected

[Curtis Mattoon]

FWIW, usermod -a -G <group> <username> is also valid.

[ijk]

"You need to be a member of group 'disk' to be able to write to the SD card." This is wrong and dangerous.