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I'm trying to set up a Raspberry Pi to run BitTorrent Sync to back up my files to an external hard drive, but I'm running into some frustrating issues.

First, I need to set up the USB hard drive to auto-mount on boot, because the power frequently goes out where I live. So, I added a line to /etc/fstab

/dev/sda1   /media/josiah    vfat    defaults   0   0

I rebooted, and it mounted the drive, but then btsync couldn't write to it. So, I did a little reading and found that you have to specify the user option, so I tried this;

/dev/sda1   /media/josiah    vfat    defaults,user   0   0

That didn't seem to work either, so I tried specifying all of the defaults manually

/dev/sda1   /media/josiah    vfat    rw,auto,user,async,suid,dev,exec    0   0

I thought it was working, but then btsync started complaining again that it couldn't write to the drive, and when I tried to unmount it as a normal user it said that only a super user can unmount the drive.

That's confusing to me, since I thought that's what the user option was for. What am I missing, or doing wrong?

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up vote 14 down vote accepted

You can do a chmod after you mounted the partition, but that wouldn't be persistent accross reboots.

You should try this fstab line:

/dev/sda1   /media/josiah    vfat    user,umask=0000   0   0

Or this mount options:

mount -t vfat -ouser,umask=0000 /dev/sda1 /media/josiah

That will make the mounted partition world readable and writable.

If you need a less permissive setup, you should create a new group and mount as follows:

mount -t vfat -ouser,gid=1010,umask=0007 /dev/sda1 /media/josiah

It assumes your new group's gid is 1010. All users that need access to the mountpoint will need to be added to the new group.

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That fstab line worked. Thank you! – Josiah Sprague Jul 10 '13 at 4:28

Edit the permissions for the mount directory.

In your case, chmod 777 /media/josiah ought to do the trick quite nicely.

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Which line should I be using in /etc/fstab to auto mount the drive? – Josiah Sprague Jul 10 '13 at 3:55
Also, that command still isn't allowing me to write to the drive. – Josiah Sprague Jul 10 '13 at 3:58
have you tried mounting the directory manually and attempted a basic copy/write with a standard user? – Scandalist Jul 10 '13 at 4:02
Manually works fine. I'm trying to get it to work automatically on boot. – Josiah Sprague Jul 10 '13 at 4:04
Okay, your fstab looks fine, (Looking at your last example) are you sure the external drive is formatted vfat? – Scandalist Jul 10 '13 at 4:07

The "user" option just let the user mount the device, it has no relation to access rights for the file.

As in gnp answer, see "uid"/"gid" and "umask" option.

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