When mounting VirtualBox folders shared by Windows with mount -t vboxsf <shared folder> <mountpoint> on a Unix machine, the permissions of files and folders are often incorrect. Both files and folders are mounted with umask 000.

As a workaround I mount shared folders with the following options:

mount -t vboxsf -o uid=<username>,gid=<username>,fmask=122,dmask=022 <shared folder> <mountpoint>

The options enforce ownership and umasks for files and folders. This means that both ownership and permissions from the original file system are overridden. This could be not what you actually intend, especially when mounting Unix file systems. However, for Windows file systems I consider it a useful workaround because ownership and permissions become more useful for daily work.

The command translates to the following entry in /etc/fstab:

<shared folder> <mountpoint> vboxsf uid=<username>,gid=<username>,fmask=122,dmask=022 0 0