This hook is used to mount and unmount FiST generated stackable file systems (http://www.filesystems.org). This hook includes the list sample file systems included with the FiST. To add your own stackable file system to the list of file systems handled by this hook, set the STACKFS environment variable to a space separated list of file system names. If you need extra mount options, set the environment variable STACKOPTS.
You must set LOWERFS to the type of file system you want to mount. If modprobe can not find your stackable module, then you need to set MODDIR to the location of your modules.
The lower level file system is mounted on /n/lower by default. The LOWERROOT environment variable overrides this value.