diff --git a/lib/libc/gen/err.c b/lib/libc/gen/err.c
index 24ea242560b8..cdce20af5a91 100644
--- a/lib/libc/gen/err.c
+++ b/lib/libc/gen/err.c
@@ -1,196 +1,223 @@
 /*-
  * SPDX-License-Identifier: BSD-3-Clause
  *
  * Copyright (c) 1993
  *	The Regents of the University of California.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  * 3. Neither the name of the University nor the names of its contributors
  *    may be used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #include "namespace.h"
+#include <sys/exterrvar.h>
 #include <err.h>
 #include <errno.h>
+#include <exterr.h>
 #include <stdarg.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include "un-namespace.h"
 
 #include "libc_private.h"
 
 static FILE *err_file; /* file to use for error output */
 static void (*err_exit)(int);
 
+static void verrci(bool doexterr, int eval, int code, const char *fmt,
+    va_list ap) __printf0like(4, 0) __dead2;
+static void vwarnci(bool doexterr, int code, const char *fmt, va_list ap)
+    __printf0like(3, 0);
+
 /*
  * This is declared to take a `void *' so that the caller is not required
  * to include <stdio.h> first.  However, it is really a `FILE *', and the
  * manual page documents it as such.
  */
 void
 err_set_file(void *fp)
 {
 	if (fp)
 		err_file = fp;
 	else
 		err_file = stderr;
 }
 
 void
 err_set_exit(void (*ef)(int))
 {
 	err_exit = ef;
 }
 
 __weak_reference(_err, err);
 
 void
 _err(int eval, const char *fmt, ...)
 {
 	va_list ap;
 	va_start(ap, fmt);
-	verrc(eval, errno, fmt, ap);
+	verrci(true, eval, errno, fmt, ap);
 	va_end(ap);
 }
 
 void
 verr(int eval, const char *fmt, va_list ap)
 {
-	verrc(eval, errno, fmt, ap);
+	verrci(true, eval, errno, fmt, ap);
 }
 
 void
 errc(int eval, int code, const char *fmt, ...)
 {
 	va_list ap;
 	va_start(ap, fmt);
-	verrc(eval, code, fmt, ap);
+	verrci(false, eval, code, fmt, ap);
 	va_end(ap);
 }
 
 void
 verrc(int eval, int code, const char *fmt, va_list ap)
 {
+	verrci(false, eval, code, fmt, ap);
+}
+
+static void
+vexterr(bool doexterr, int code, const char *fmt, va_list ap)
+{
+	char exterr[UEXTERROR_MAXLEN];	/* libc knows the buffer size */
+	int extstatus;
+
+	if (doexterr)
+		extstatus = uexterr_gettext(exterr, sizeof(exterr));
 	if (err_file == NULL)
 		err_set_file(NULL);
 	fprintf(err_file, "%s: ", _getprogname());
 	if (fmt != NULL) {
 		vfprintf(err_file, fmt, ap);
 		fprintf(err_file, ": ");
 	}
-	fprintf(err_file, "%s\n", strerror(code));
+	fprintf(err_file, "%s", strerror(code));
+	if (doexterr && extstatus == 0)
+		fprintf(err_file, " (extended error %s)", exterr);
+	fprintf(err_file, "\n");
+}
+
+static void
+verrci(bool doexterr, int eval, int code, const char *fmt, va_list ap)
+{
+	vexterr(doexterr, code, fmt, ap);
 	if (err_exit)
 		err_exit(eval);
 	exit(eval);
 }
 
 void
 errx(int eval, const char *fmt, ...)
 {
 	va_list ap;
 	va_start(ap, fmt);
 	verrx(eval, fmt, ap);
 	va_end(ap);
 }
 
 void
 verrx(int eval, const char *fmt, va_list ap)
 {
 	if (err_file == NULL)
 		err_set_file(NULL);
 	fprintf(err_file, "%s: ", _getprogname());
 	if (fmt != NULL)
 		vfprintf(err_file, fmt, ap);
 	fprintf(err_file, "\n");
 	if (err_exit)
 		err_exit(eval);
 	exit(eval);
 }
 
 __weak_reference(_warn, warn);
 
 void
 _warn(const char *fmt, ...)
 {
 	va_list ap;
 	va_start(ap, fmt);
 	vwarnc(errno, fmt, ap);
 	va_end(ap);
 }
 
 void
 vwarn(const char *fmt, va_list ap)
 {
 	vwarnc(errno, fmt, ap);
 }
 
 void
 warnc(int code, const char *fmt, ...)
 {
 	va_list ap;
 	va_start(ap, fmt);
 	vwarnc(code, fmt, ap);
 	va_end(ap);
 }
 
 void
 vwarnc(int code, const char *fmt, va_list ap)
+{
+	vwarnci(false, code, fmt, ap);
+}
+
+static void
+vwarnci(bool doexterr, int code, const char *fmt, va_list ap)
 {
 	int saved_errno;
 
 	saved_errno = errno;
-	if (err_file == NULL)
-		err_set_file(NULL);
-	fprintf(err_file, "%s: ", _getprogname());
-	if (fmt != NULL) {
-		vfprintf(err_file, fmt, ap);
-		fprintf(err_file, ": ");
-	}
-	fprintf(err_file, "%s\n", strerror(code));
+	vexterr(doexterr, code, fmt, ap);
 	errno = saved_errno;
 }
 
 void
 warnx(const char *fmt, ...)
 {
 	va_list ap;
 	va_start(ap, fmt);
 	vwarnx(fmt, ap);
 	va_end(ap);
 }
 
 void
 vwarnx(const char *fmt, va_list ap)
 {
 	int saved_errno;
 
 	saved_errno = errno;
 	if (err_file == NULL)
 		err_set_file(NULL);
 	fprintf(err_file, "%s: ", _getprogname());
 	if (fmt != NULL)
 		vfprintf(err_file, fmt, ap);
 	fprintf(err_file, "\n");
 	errno = saved_errno;
 }