In previous Solaris releases, /etc/mnttab was a text-based file that stored information about mounted file systems. The downside of being a file was that it could get out of sync with the actual state of mounted file systems.
Now the /etc/mnttab file is a MNTFS file system that provides read-only information directly from the kernel about mounted file systems for the local system.
Note the following mnttab behavior changes:
Programs or scripts attempting to write to /etc/mnttab will fail.
The mount -m option for faking mnttab entries no longer works.
No administration is required for the /etc/mnttab mount table.
See mnttab(4) for more information.