Index: head/usr.bin/uname/uname.1
===================================================================
--- head/usr.bin/uname/uname.1
+++ head/usr.bin/uname/uname.1
@@ -28,7 +28,7 @@
 .\"	@(#)uname.1	8.3 (Berkeley) 4/8/94
 .\" $FreeBSD$
 .\"
-.Dd May 31, 2017
+.Dd June 27, 2019
 .Dt UNAME 1
 .Os
 .Sh NAME
@@ -36,7 +36,7 @@
 .Nd display information about the system
 .Sh SYNOPSIS
 .Nm
-.Op Fl aiKmnoprsUv
+.Op Fl abiKmnoprsUv
 .Sh DESCRIPTION
 The
 .Nm
@@ -53,6 +53,8 @@
 and
 .Fl v
 were specified.
+.It Fl b
+Write the kernel's linker-generated build-id to standard output.
 .It Fl i
 Write the kernel ident to standard output.
 .It Fl K
@@ -152,3 +154,7 @@
 .Fl U
 extension flags appeared in
 .Fx 10.0 .
+The
+.Fl b
+extension flag appeared in
+.Fx 13.0 .
Index: head/usr.bin/uname/uname.c
===================================================================
--- head/usr.bin/uname/uname.c
+++ head/usr.bin/uname/uname.c
@@ -67,9 +67,10 @@
 #define	IFLAG	0x40
 #define	UFLAG	0x80
 #define	KFLAG	0x100
+#define	BFLAG	0x200
 
 typedef void (*get_t)(void);
-static get_t get_ident, get_platform, get_hostname, get_arch,
+static get_t get_buildid, get_ident, get_platform, get_hostname, get_arch,
     get_release, get_sysname, get_kernvers, get_uservers, get_version;
 
 static void native_ident(void);
@@ -81,11 +82,13 @@
 static void native_version(void);
 static void native_kernvers(void);
 static void native_uservers(void);
+static void native_buildid(void);
 static void print_uname(u_int);
 static void setup_get(void);
 static void usage(void);
 
-static char *ident, *platform, *hostname, *arch, *release, *sysname, *version, *kernvers, *uservers;
+static char *buildid, *ident, *platform, *hostname, *arch, *release, *sysname,
+    *version, *kernvers, *uservers;
 static int space;
 
 int
@@ -97,11 +100,14 @@
 	setup_get();
 	flags = 0;
 
-	while ((ch = getopt(argc, argv, "aiKmnoprsUv")) != -1)
+	while ((ch = getopt(argc, argv, "abiKmnoprsUv")) != -1)
 		switch(ch) {
 		case 'a':
 			flags |= (MFLAG | NFLAG | RFLAG | SFLAG | VFLAG);
 			break;
+		case 'b':
+			flags |= BFLAG;
+			break;
 		case 'i':
 			flags |= IFLAG;
 			break;
@@ -169,6 +175,7 @@
 	CHECK_ENV("i", ident);
 	CHECK_ENV("K", kernvers);
 	CHECK_ENV("U", uservers);
+	CHECK_ENV("b", buildid);
 }
 
 #define	PRINT_FLAG(flags,flag,var)		\
@@ -194,6 +201,7 @@
 	PRINT_FLAG(flags, IFLAG, ident);
 	PRINT_FLAG(flags, KFLAG, kernvers);
 	PRINT_FLAG(flags, UFLAG, uservers);
+	PRINT_FLAG(flags, BFLAG, buildid);
 	printf("\n");
 }
 
@@ -261,6 +269,9 @@
 NATIVE_SYSCTLNAME_GET(ident, "kern.ident") {
 } NATIVE_SET;
 
+NATIVE_SYSCTLNAME_GET(buildid, "kern.build_id") {
+} NATIVE_SET;
+
 static void
 native_uservers(void)
 {
@@ -282,6 +293,6 @@
 static void
 usage(void)
 {
-	fprintf(stderr, "usage: uname [-aiKmnoprsUv]\n");
+	fprintf(stderr, "usage: uname [-abiKmnoprsUv]\n");
 	exit(1);
 }