Index: head/bin/dd/args.c
===================================================================
--- head/bin/dd/args.c
+++ head/bin/dd/args.c
@@ -41,7 +41,7 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
-#include <sys/types.h>
+#include <sys/param.h>
 
 #include <ctype.h>
 #include <err.h>
@@ -57,6 +57,7 @@
 
 static int	c_arg(const void *, const void *);
 static int	c_conv(const void *, const void *);
+static int	c_oflag(const void *, const void *);
 static void	f_bs(char *);
 static void	f_cbs(char *);
 static void	f_conv(char *);
@@ -67,6 +68,7 @@
 static void	f_if(char *);
 static void	f_obs(char *);
 static void	f_of(char *);
+static void	f_oflag(char *);
 static void	f_seek(char *);
 static void	f_skip(char *);
 static void	f_speed(char *);
@@ -90,6 +92,7 @@
 	{ "iseek",	f_skip,		C_SKIP,	 C_SKIP },
 	{ "obs",	f_obs,		C_OBS,	 C_BS|C_OBS },
 	{ "of",		f_of,		C_OF,	 C_OF },
+	{ "oflag",	f_oflag,	0,	 0 },
 	{ "oseek",	f_seek,		C_SEEK,	 C_SEEK },
 	{ "seek",	f_seek,		C_SEEK,	 C_SEEK },
 	{ "skip",	f_skip,		C_SKIP,	 C_SKIP },
@@ -348,8 +351,8 @@
 
 	while (arg != NULL) {
 		tmp.name = strsep(&arg, ",");
-		cp = bsearch(&tmp, clist, sizeof(clist) / sizeof(struct conv),
-		    sizeof(struct conv), c_conv);
+		cp = bsearch(&tmp, clist, nitems(clist), sizeof(struct conv),
+		    c_conv);
 		if (cp == NULL)
 			errx(1, "unknown conversion %s", tmp.name);
 		if (ddflags & cp->noset)
@@ -366,6 +369,37 @@
 
 	return (strcmp(((const struct conv *)a)->name,
 	    ((const struct conv *)b)->name));
+}
+
+static const struct oflag {
+	const char *name;
+	uint64_t set;
+} olist[] = {
+	{ "fsync",	C_OFSYNC },
+	{ "sync",	C_OFSYNC },
+};
+
+static void
+f_oflag(char *arg)
+{
+	struct oflag *op, tmp;
+
+	while (arg != NULL) {
+		tmp.name = strsep(&arg, ",");
+		op = bsearch(&tmp, olist, nitems(olist), sizeof(struct oflag),
+		    c_oflag);
+		if (op == NULL)
+			errx(1, "unknown open flag %s", tmp.name);
+		ddflags |= op->set;
+	}
+}
+
+static int
+c_oflag(const void *a, const void *b)
+{
+
+	return (strcmp(((const struct oflag *)a)->name,
+	    ((const struct oflag *)b)->name));
 }
 
 static intmax_t
Index: head/bin/dd/dd.h
===================================================================
--- head/bin/dd/dd.h
+++ head/bin/dd/dd.h
@@ -103,6 +103,7 @@
 #define	C_PROGRESS	0x0000000040000000ULL
 #define	C_FSYNC		0x0000000080000000ULL
 #define	C_FDATASYNC	0x0000000100000000ULL
+#define	C_OFSYNC	0x0000000200000000ULL
 
 #define	C_PARITY	(C_PAREVEN | C_PARODD | C_PARNONE | C_PARSET)
 
Index: head/bin/dd/dd.1
===================================================================
--- head/bin/dd/dd.1
+++ head/bin/dd/dd.1
@@ -123,6 +123,19 @@
 .Cm oseek
 operand),
 the output file is truncated at that point.
+.It Cm oflag Ns = Ns Ar value Ns Op , Ns Ar value ...
+Where
+.Cm value
+is one of the symbols from the following list.
+.Bl -tag -width "fsync"
+.It Cm fsync
+Set the O_FSYNC flag on the output file to make writes synchronous.
+.It Cm sync
+Set the O_SYNC flag on the output file to make writes synchronous.
+This is synonymous with the
+.Cm fsync
+value.
+.El
 .It Cm oseek Ns = Ns Ar n
 Seek on the output file
 .Ar n
Index: head/bin/dd/dd.c
===================================================================
--- head/bin/dd/dd.c
+++ head/bin/dd/dd.c
@@ -143,6 +143,7 @@
 setup(void)
 {
 	u_int cnt;
+	int oflags;
 	cap_rights_t rights;
 	unsigned long cmds[] = { FIODTYPE, MTIOCTOP };
 
@@ -171,17 +172,28 @@
 		/* No way to check for read access here. */
 		out.fd = STDOUT_FILENO;
 		out.name = "stdout";
+		if (ddflags & C_OFSYNC) {
+			oflags = fcntl(out.fd, F_GETFL);
+			if (oflags == -1)
+				err(1, "unable to get fd flags for stdout");
+			oflags |= O_FSYNC;
+			if (fcntl(out.fd, F_SETFL, oflags) == -1)
+				err(1, "unable to set fd flags for stdout");
+		}
 	} else {
-#define	OFLAGS \
-    (O_CREAT | (ddflags & (C_SEEK | C_NOTRUNC) ? 0 : O_TRUNC))
-		out.fd = open(out.name, O_RDWR | OFLAGS, DEFFILEMODE);
+		oflags = O_CREAT;
+		if (!(ddflags & (C_SEEK | C_NOTRUNC)))
+			oflags |= O_TRUNC;
+		if (ddflags & C_OFSYNC)
+			oflags |= O_FSYNC;
+		out.fd = open(out.name, O_RDWR | oflags, DEFFILEMODE);
 		/*
 		 * May not have read access, so try again with write only.
 		 * Without read we may have a problem if output also does
 		 * not support seeks.
 		 */
 		if (out.fd == -1) {
-			out.fd = open(out.name, O_WRONLY | OFLAGS, DEFFILEMODE);
+			out.fd = open(out.name, O_WRONLY | oflags, DEFFILEMODE);
 			out.flags |= NOREAD;
 			cap_rights_clear(&rights, CAP_READ);
 		}