better words for -b, wiyh help from jmc@

1 files changed, 12 insertions, 3 deletions

diff --git a/sbin/fsck_ffs/fsck_ffs.8 b/sbin/fsck_ffs/fsck_ffs.8
index 28d8287e028..8a05f95a4f7 100644
--- a/sbin/fsck_ffs/fsck_ffs.8
+++ b/sbin/fsck_ffs/fsck_ffs.8
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: fsck_ffs.8,v 1.25 2015/10/14 14:33:45 deraadt Exp $
+.\"	$OpenBSD: fsck_ffs.8,v 1.26 2016/09/01 13:48:15 otto Exp $
 .\"	$NetBSD: fsck_ffs.8,v 1.12 1996/09/23 16:18:34 christos Exp $
 .\"
 .\" Copyright (c) 1980, 1989, 1991, 1993
@@ -30,7 +30,7 @@
 .\"
 .\"	@(#)fsck.8	8.3 (Berkeley) 11/29/94
 .\"
-.Dd $Mdocdate: October 14 2015 $
+.Dd $Mdocdate: September 1 2016 $
 .Dt FSCK_FFS 8
 .Os
 .Sh NAME
@@ -140,7 +140,16 @@ Use the
 .Ar block#
 specified as
 the super block for the file system.
-Block 32 is usually an alternate super block.
+If the primary superblock is corrupted
+.Nm
+tries to find a valid alternate superblock based on the
+information in the disklabel.
+If that fails, a number printed by
+.Nm newfs
+(using
+.Fl N
+combined with the original flags used to create the filesystem)
+can be used as a value to this argument.
 .It Fl c Ar level
 Convert the file system to the specified
 .Ar level .