I have a few SD cards from 1 GB to 4 GB and two machines running Debian 10.4, one laptop and one PC.

On the PC, all of those SD cards are writable. On the Acer laptop none of them. As the Acer Laptop got Windows 7 installed, too, those SD cards are read-only with Windows, too, in the same way as with Linux. From the Acer manual, I couldn't figure out, why those SD cards are read-only. At least, the manual talks about a "card reader".

By chance, I saw a difference between those two machines in the /dev directory. The PC has always an entry like "/dev/sdx" and "/etc/sdx1" meanwhile the laptop has an entry "/dev/mmcblk0" and "/dev/mmcblk0p1".

"sudo dmesg" on the laptop also is saying:

Does this indicate, that the Acer laptop hasn't been built for some reason to write on an SD card?

Take a look at the permissions on the device names where the cards are mounted. See if you have write permissions on these devices. Open a terminal and type in these commands:


ls -l /dev/sdx

ls -l /dev/mmcblk0

ls -l /dev/mmcblk0p1

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Steve Stites

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They are all the same:

On the PC side, all the sd? devices have the same permissions, too. If I go as root to the appropriate /media/... directory and try to create a file there, e.g., "dmesg > d.txt", then I also get an error message that it is a read-only file system.

As with Windows happens the same, i.e. you cannot write onto or format the SD card, I got the impression that it might be a restriction built into the device. Maybe it is actually only a "card reader". A reader that cannot write ...

It is quite possible that it is just a reader.

I have two adapters, one is a USB reader & the other is a read/write adapter.
(The first one I bought, I thought would write too, but it doesn't.)

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