The generic file system commands determine the file system type by following this sequence:
From the -F option, if supplied.
By matching a special device with an entry in /etc/vfstab file (if special is supplied). For example, fsck first looks for a match against the fsck device field; if no match is found, it then checks the special device field.
By using the default specified in /etc/default/fs for local file systems and in /etc/dfs/fstypes for remote file systems.