dmesg(8) first appeared in 3BSD.

http://minnie.tuhs.org/cgi-bin/utree.pl?file=3BSD/usr/man/man1/dmesg.1m

PR:		212443
Approved by:	bcr (mentor)
Obtained from:	TUHS
MFC after:	4 days
Differential Revision:	https://reviews.freebsd.org/D8105

sbin/dmesg/dmesg.8

@@ -28,7 +28,7 @@
 .\"     @(#)dmesg.8	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd May 9, 2013
+.Dd October 3, 2016
 .Dt DMESG 8
 .Os
 .Sh NAME
@@ -84,4 +84,4 @@ at startup time
 The
 .Nm
 utility appeared in
-.Bx 4.0 .
+.Bx 3 .