-will not request new statistics from the filesystems,
-but will respond with the possibly stale statistics
-that were previously obtained.
+will not request new statistics from the filesystems, but will respond
+with the possibly stale statistics that were previously obtained.
+.It Fl t
+Only print out statistics for filesystems of the specified types.
+More than one type may be specified in a comma separated list.
+The list of filesystem types can be prefixed with
+.Dq no
+to specify the filesystem types for which action should
+.Em not
+be taken.
+For example, the
+.Nm df
+command:
+.Bd -literal -offset indent
+df -t nonfs,mfs
+.Ed
+.Pp
+lists all filesystems except those of type
+.Tn NFS
+and
+.Tn MFS .
+The
+.Xr sysctl 8
+command can be used to find out the types of filesystems
+that are available on the system:
+.Bd -literal -offset indent
+sysctl vfs
+.Ed
+.El
+.Sh ENVIRONMENTAL VARIABLES
+.Bl -tag -width BLOCKSIZE
+.It Ev BLOCKSIZE
+If the environmental variable
+.Ev BLOCKSIZE
+is set, the block counts will be displayed in units of that size block.
+.El