On many Unix systems, /etc/mnttab is a file listing all the filesystems that are currently mounted. On older Unixes, it is an actual text file, updated everytime a filesystem is mounted or unmounted. This can cause problems
if multiple filesystems are trying to mount or unmount at the same time, and often results in the file being out of sync with the actual kernel state. To avoid these problems, some newer Unixes, such as Solaris 8, make /etc/mnttab be a special file or filesystem that just shows the
current state of the kernel mount table whenever it is read.