diff --git a/umount.c b/umount.c
index 23b9ff7..b205812 100644
--- a/umount.c
+++ b/umount.c
@@ -1,23 +1,30 @@
 /* See LICENSE file for copyright and license details. */
-#include <sys/mount.h>
+#include <mntent.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <sys/mount.h>
 #include "util.h"
 
 static void
 usage(void)
 {
-	eprintf("usage: %s [-lfn] target\n", argv0);
+	eprintf("usage: %s [-alfn] target\n", argv0);
 }
 
 int
 main(int argc, char *argv[])
 {
 	int i;
+	int aflag = 0;
 	int flags = 0;
 	int ret = EXIT_SUCCESS;
+	FILE *fp;
+	struct mntent *me;
 
 	ARGBEGIN {
+	case 'a':
+		aflag = 1;
+		break;
 	case 'f':
 		flags |= MNT_FORCE;
 		break;
@@ -30,9 +37,23 @@ main(int argc, char *argv[])
 		usage();
 	} ARGEND;
 
-	if (argc < 1)
+	if (argc < 1 && aflag == 0)
 		usage();
 
+	if (aflag == 1) {
+		fp = setmntent("/etc/fstab", "r");
+		if (!fp)
+			eprintf("setmntent %s:", "/etc/fstab");
+		while ((me = getmntent(fp))) {
+			if (umount2(me->mnt_dir, flags) < 0) {
+				perror("umount2:");
+				ret = EXIT_FAILURE;
+			}
+		}
+		endmntent(fp);
+		return ret;
+	}
+
 	for (i = 0; i < argc; i++) {
 		if (umount2(argv[i], flags) < 0)
 			perror("umount2:");