BBB SD-Card external storage, format, Permission denied

Embedded Linux Discussions
1

Hello,
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.

mmcdev=1
bootpart=1:2
mmcroot=/dev/mmcblk1p2 ro
optargs=quiet

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 with read and write permission?

Thanks in advance

2

Sorry, that is an untrue statement… FAT file systems do not understand permissions.

While that is how you setup the media in fstab, let’s see how it was actually mounted, please run:

mount | grep mmc

Regards,

3

Hello Robert,
Thank you for your quick reply.

debian@beaglebone:~$ mount |grep mmc
/dev/mmcblk1p1 on / type ext4 (rw,noatime,errors=remount-ro,data=ordered)
/dev/mmcblk0p1 on /home/debian/BackUp type vfat (rw,nosuid,nodev,noexec,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro,user)
4

in fstab tie this mount point to a user…

debian@BeagleBone:~$ mount | grep sda
/dev/sda1 on /home/debian/BackUp type vfat (rw,nosuid,nodev,noexec,relatime,uid=1000,gid=1000,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro,user)
debian@BeagleBone:~$ cd BackUp/
debian@BeagleBone:~/BackUp$ touch test.txt
debian@BeagleBone:~/BackUp$ mkdir folder
debian@BeagleBone:~/BackUp$ touch folder/test.txt
debian@BeagleBone:~/BackUp$ tree
.
├── folder
│   └── test.txt
└── test.txt

1 directory, 2 files
debian@BeagleBone:~/BackUp$ rm folder/test.txt 
debian@BeagleBone:~/BackUp$ tree
.
├── folder
└── test.txt

1 directory, 1 file

fstab:

debian@BeagleBone:~/BackUp$ cat /etc/fstab | grep sda
/dev/sda1 /home/debian/BackUp auto auto,rw,async,user,nofail,uid=1000,gid=1000 0 0

for example i used uid=1000 and gid=1000, so make sure that matches what your application’s user and group runs as…

Regards,

5

Thank you very much Robert,
this works for me.
/dev/mmcblk0p1 /home/debian/BackUp auto auto,rw,async,user,nofail,uid=debian,gid=debian 0 0

best regards