And make sure the datadir and wallet dir and all the files have 0777 (full user-group-other) permissions.
This is bad advice: it's good practice to give files as few permissions as necessary. Giving all users on a multi user system full access to your wallet is a terrible idea. Also, non-executable files shouldn't have an executable flag.1. Most people do not share their devices, in fact we have gravitated towards a situation where people use multiple devices.
2. Device mountpoints are notoriously bad at dealing with file permissions, particularly with older versions of user/HAL that would just mount everything as root.
3. If your Unix system gets hit with an application exploit, then it already obtained user access by virtue of the running program being owned by your user account (I will not deal with setUID madness here, but nobody should be using that horrible design anyway), and do not need the group and other bits; they might as well read your SSH keys.
The executable flag, that was a mistake. In that case they can be set to 0644.
