I am currently trying to use the SD card of the BBB as external memory. I have found hints and instructions in numerous forums.
With the following approach I have achieved the best results.
The file /etc/fstab
I added the following line.
/dev/mmcblk0p1 /home/debian/BackUp auto auto,rw,async,user,nofail 0 0
I formatted the SD card FAT and created a file uEnv.txt.
I can access the directory and I have read permissions but no write permissions. I then did some more research and read that Linux does not support FAT permissions. I tried several things and logged in as root but I can’t edit the permissions.
So what do I have to do to use an SD card Windows/Linux compatible ?