Fstab vs mtab
The mtab (contraction of mounted file systems table) file is a system information file, commonly found on Unix-like systems. This file lists all currently mounted filesystems along with their initialization options. mtab has a lot in common with fstab, the main distinction being that the latter lists all available filesystems whereas the former lists only currently mounted ones. Therefore mtab is usually in a format similar to that of fstab. Most of the time it is possible to directly use lines from mtab in fstab
Mtab, http://en.wikipedia.org/w/index.php?title=Mtab&oldid=469883015 (last visited Dec. 7, 2012).