I am using Linux Mint Cinnamon Uma.

When I put a pen drive in a usb slot, or try to mount it, I get an error message:

"Unable to mount USB Stick

Error mounting dev/sdc1 at media/grumpy/USB Stick: unknow error when mounting dev/sdc1"

It does say "unknow" rather than "unknown".

Other usb drives are working fine.

Earlier today I was copying a large file to the usb drive. The copying seemed to conclude OK. Later on I noticed that the 16GB usb drive was unmounted, even though I had not unmounted it.

1) Is there anything I can try to fix it without reformatting it?

2) What's the easiest GUI way to reformat the drive, probably to NFTS?

3) What can I do to check it, in case the hardware is defective?

Thanks,

Happy Xmas.

Happy Xmas back atcha.

It might be the drive went into read-only mode, which usually signals end of life for the device.

I recommend you try to make a virtual backup of the drive to your computer using dd. Then you can attempt to use fsck to fix, and mount the virtual drive without potentially making the physical drive worse.