Set or clear the indicated default mount options in the filesys-
tem. Default mount options can be overridden by mount options
specified either in /etc/fstab(5) or on the command line argu-
ments to mount(8). Older kernels may not support this feature;"
There are really three "defaults" of course. The filesystem implementation
level, the filesystem image level, and the /etc/fstab level, in that order.