Index: usr.sbin/bsdinstall/bsdinstall
===================================================================
--- usr.sbin/bsdinstall/bsdinstall
+++ usr.sbin/bsdinstall/bsdinstall
@@ -40,13 +40,15 @@
 
 ############################################################ GLOBALS
 
-: ${BSDINSTALL_TMPETC="/tmp/bsdinstall_etc"}; export BSDINSTALL_TMPETC
-: ${BSDINSTALL_TMPBOOT="/tmp/bsdinstall_boot"}; export BSDINSTALL_TMPBOOT
+: ${TMPDIR:="/tmp"}; export TMPDIR
+
+: ${BSDINSTALL_TMPETC="${TMPDIR}/bsdinstall_etc"}; export BSDINSTALL_TMPETC
+: ${BSDINSTALL_TMPBOOT="${TMPDIR}/bsdinstall_boot"}; export BSDINSTALL_TMPBOOT
 : ${PATH_FSTAB="$BSDINSTALL_TMPETC/fstab"}; export PATH_FSTAB
 : ${BSDINSTALL_DISTDIR="/usr/freebsd-dist"}; export BSDINSTALL_DISTDIR
 : ${BSDINSTALL_CHROOT="/mnt"}; export BSDINSTALL_CHROOT
 
-export debugFile="${debugFile-${BSDINSTALL_LOG-/tmp/bsdinstall_log}}"
+export debugFile="${debugFile-${BSDINSTALL_LOG-${TMPDIR}/bsdinstall_log}}"
 
 ############################################################ MAIN
 
Index: usr.sbin/bsdinstall/bsdinstall.8
===================================================================
--- usr.sbin/bsdinstall/bsdinstall.8
+++ usr.sbin/bsdinstall/bsdinstall.8
@@ -259,6 +259,10 @@
 Others are set by various interactive user prompts, and can be usefully
 overridden when making scripted or customized installers.
 .Bl -tag -width ".Ev BSDINSTALL_DISTSITE"
+.It Ev TMPDIR
+The directory to use for temporary files.
+Default:
+.Dq Pa /tmp
 .It Ev DISTRIBUTIONS
 The set of distributions to install, e.g., "base.txz kernel.txz ports.txz".
 Default: unset
@@ -291,7 +295,7 @@
 .It Ev BSDINSTALL_LOG
 Path to a log file for the installation.
 Default:
-.Dq Pa /tmp/bsdinstall_log
+.Dq Pa $TMPDIR/bsdinstall_log
 .It Ev BSDINSTALL_TMPETC
 Directory where files destined for the new system's
 .Pa /etc
@@ -300,7 +304,7 @@
 target is executed.
 If this directory does not already exist, it will be created.
 Default:
-.Dq Pa /tmp/bsdinstall_etc
+.Dq Pa $TMPDIR/bsdinstall_etc
 .It Ev BSDINSTALL_TMPBOOT
 Directory where files destined for the new system's
 .Pa /boot
@@ -309,7 +313,7 @@
 target is executed.
 If this directory does not already exist, it will be created.
 Default:
-.Dq Pa /tmp/bsdinstall_boot
+.Dq Pa $TMPDIR/bsdinstall_boot
 .It Ev ZFSBOOT_POOL_NAME
 Name for the pool containing the base system.
 Default:
Index: usr.sbin/bsdinstall/partedit/gpart_ops.c
===================================================================
--- usr.sbin/bsdinstall/partedit/gpart_ops.c
+++ usr.sbin/bsdinstall/partedit/gpart_ops.c
@@ -711,10 +711,11 @@
 	if (strcmp(type, bootpart_type(scheme, &default_bootmount)) == 0) {
 		if (default_bootmount == NULL) {
 
-			int fd = open("/tmp/bsdinstall-esps", O_CREAT | O_WRONLY | O_APPEND,
-						  0600);
+			int fd = openat(tmpdfd, "bsdinstall-esps",
+			    O_CREAT | O_WRONLY | O_APPEND, 0600);
 			if (fd > 0) {
 				write(fd, md->name, strlen(md->name));
+				write(fd, "\n", 1);
 				close(fd);
 			}
 
Index: usr.sbin/bsdinstall/partedit/partedit.h
===================================================================
--- usr.sbin/bsdinstall/partedit/partedit.h
+++ usr.sbin/bsdinstall/partedit/partedit.h
@@ -39,6 +39,8 @@
 struct gmesh;
 struct ggeom;
 
+extern int tmpdfd;
+
 TAILQ_HEAD(pmetadata_head, partition_metadata);
 extern struct pmetadata_head part_metadata;
 
Index: usr.sbin/bsdinstall/partedit/partedit.c
===================================================================
--- usr.sbin/bsdinstall/partedit/partedit.c
+++ usr.sbin/bsdinstall/partedit/partedit.c
@@ -32,17 +32,20 @@
 
 #include <dialog.h>
 #include <dlg_keys.h>
+#include <err.h>
 #include <errno.h>
 #include <fstab.h>
 #include <inttypes.h>
 #include <libgeom.h>
 #include <libutil.h>
 #include <stdlib.h>
+#include <sysexits.h>
 
 #include "diskeditor.h"
 #include "partedit.h"
 
 struct pmetadata_head part_metadata;
+int tmpdfd;
 static int sade_mode = 0;
 
 static int apply_changes(struct gmesh *mesh);
@@ -66,6 +69,8 @@
 
 	end_dialog();
 
+	close(tmpdfd);
+
 	exit(1);
 }
 
@@ -73,7 +78,7 @@
 main(int argc, const char **argv)
 {
 	struct partition_metadata *md;
-	const char *progname, *prompt;
+	const char *progname, *prompt, *tmpdir;
 	struct partedit_item *items = NULL;
 	struct gmesh mesh;
 	int i, op, nitems, nscroll;
@@ -85,8 +90,17 @@
 
 	TAILQ_INIT(&part_metadata);
 
+	tmpdir = getenv("TMPDIR");
+	if (tmpdir == NULL)
+		tmpdir = "/tmp";
+	tmpdfd = open(tmpdir, O_RDWR | O_DIRECTORY);
+	if (tmpdfd < 0)
+		err(EX_OSERR, "%s", tmpdir);
+
 	init_fstab_metadata();
 
+	unlinkat(tmpdfd, "bsdinstall-esps", 0);
+
 	init_dialog(stdin, stdout);
 	if (!sade_mode)
 		dialog_vars.backtitle = __DECONST(char *, "FreeBSD Installer");
@@ -221,6 +235,8 @@
 	free(items);
 	end_dialog();
 
+	close(tmpdfd);
+
 	return (error);
 }
 
Index: usr.sbin/bsdinstall/scripts/bootconfig
===================================================================
--- usr.sbin/bsdinstall/scripts/bootconfig
+++ usr.sbin/bsdinstall/scripts/bootconfig
@@ -30,6 +30,8 @@
 BSDCFG_SHARE="/usr/share/bsdconfig"
 . $BSDCFG_SHARE/common.subr || exit 1
 
+: ${TMPDIR:="/tmp"}
+
 die() {
 	echo $*
 	exit 1
@@ -50,8 +52,8 @@
 fi
 
 if [ "$(uname -m)" = "arm64" ] || [ "$X86_BOOTMETHOD" = "UEFI" ]; then
-	UFSBOOT_ESPS=$(cat /tmp/bsdinstall-esps 2>/dev/null)
-	ZFSBOOT_DISKS=$(cat /tmp/bsdinstall-zfsboot 2>/dev/null)
+	UFSBOOT_ESPS=$(cat $TMPDIR/bsdinstall-esps 2>/dev/null)
+	ZFSBOOT_DISKS=$(cat $TMPDIR/bsdinstall-zfsboot 2>/dev/null)
 	num_esps=0
 
 	if [ -n "$ZFSBOOT_DISKS" ]; then
@@ -99,7 +101,7 @@
 					continue
 				fi
 
-				mntpt=$(mktemp -d /tmp/stand-test.XXXXXX)
+				mntpt=$(mktemp -d $TMPDIR/stand-test.XXXXXX)
 				if [ -e "/dev/${geom}p${index}" ]; then
 					dev=${geom}p${index}
 				elif [ -e "/dev/${geom}s${index}" ]; then
@@ -129,7 +131,7 @@
 			die "Failed to format ESP $esp as FAT32"
 		fi
 
-		mntpt=$(mktemp -d /tmp/stand-test.XXXXXX)
+		mntpt=$(mktemp -d $TMPDIR/stand-test.XXXXXX)
 		f_dprintf "Mounting ESP /dev/${esp}"
 		mount -t msdosfs "/dev/${esp}" "${mntpt}"
 		if [ $? -ne 0 ]; then
Index: usr.sbin/bsdinstall/scripts/mount
===================================================================
--- usr.sbin/bsdinstall/scripts/mount
+++ usr.sbin/bsdinstall/scripts/mount
@@ -26,7 +26,7 @@
 #
 # $FreeBSD$
 
-TMP_FSTAB=/tmp/bsdinstall-tmp-fstab
+TMP_FSTAB=${TMPDIR:-"/tmp"}/bsdinstall-tmp-fstab
 
 cat $PATH_FSTAB | awk -v BSDINSTALL_CHROOT=$BSDINSTALL_CHROOT '{
 	if ($2 ~ "^/.*") {
Index: usr.sbin/bsdinstall/scripts/script
===================================================================
--- usr.sbin/bsdinstall/scripts/script
+++ usr.sbin/bsdinstall/scripts/script
@@ -49,6 +49,8 @@
 
 ############################################################ GLOBALS
 
+: ${TMPDIR:="/tmp"}
+
 #
 # Strings that should be moved to an i18n file and loaded with f_include_lang()
 #
@@ -88,9 +90,9 @@
 rm -rf $BSDINSTALL_TMPETC
 mkdir $BSDINSTALL_TMPETC
 
-split -a 2 -p '^#!.*' "$SCRIPT" /tmp/bsdinstall-installscript-
+split -a 2 -p '^#!.*' "$SCRIPT" $TMPDIR/bsdinstall-installscript-
 
-. /tmp/bsdinstall-installscript-aa
+. $TMPDIR/bsdinstall-installscript-aa
 : ${DISTRIBUTIONS="kernel.txz base.txz"}; export DISTRIBUTIONS
 export BSDINSTALL_DISTDIR
 
@@ -135,8 +137,8 @@
 fi
 
 # Run post-install script
-if [ -f /tmp/bsdinstall-installscript-ab ]; then
-	cp /tmp/bsdinstall-installscript-ab $BSDINSTALL_CHROOT/tmp/installscript
+if [ -f $TMPDIR/bsdinstall-installscript-ab ]; then
+	cp $TMPDIR/bsdinstall-installscript-ab $BSDINSTALL_CHROOT/tmp/installscript
 	chmod a+x $BSDINSTALL_CHROOT/tmp/installscript
 	mount -t devfs devfs "$BSDINSTALL_CHROOT/dev"
 	chroot $BSDINSTALL_CHROOT /tmp/installscript $@ 2>&1
Index: usr.sbin/bsdinstall/scripts/umount
===================================================================
--- usr.sbin/bsdinstall/scripts/umount
+++ usr.sbin/bsdinstall/scripts/umount
@@ -26,7 +26,7 @@
 #
 # $FreeBSD$
 
-TMP_FSTAB=/tmp/bsdinstall-tmp-fstab
+TMP_FSTAB=${TMPDIR:-"/tmp"}/bsdinstall-tmp-fstab
 
 cat $PATH_FSTAB | awk -v BSDINSTALL_CHROOT=$BSDINSTALL_CHROOT '{
 	if ($2 ~ "^/.*") {
Index: usr.sbin/bsdinstall/scripts/zfsboot
===================================================================
--- usr.sbin/bsdinstall/scripts/zfsboot
+++ usr.sbin/bsdinstall/scripts/zfsboot
@@ -1171,7 +1171,7 @@
 			f_dprintf "$funcname: For encrypted root disk..."
 
 		# Create parent directory for boot pool
-		f_eval_catch -d $funcname umount "$UMOUNT" /mnt
+		f_eval_catch -d $funcname umount "$UMOUNT" "$BSDINSTALL_CHROOT"
 		f_eval_catch $funcname mount "$MOUNT_TYPE" tmpfs none \
 		             $BSDINSTALL_CHROOT || return $FAILURE
 
@@ -1273,7 +1273,8 @@
 		# Clean up
 		f_eval_catch $funcname zfs "$ZFS_UNMOUNT" "$bootpool_name" ||
 			return $FAILURE
-		f_eval_catch -d $funcname umount "$UMOUNT" /mnt # tmpfs
+		# tmpfs
+		f_eval_catch -d $funcname umount "$UMOUNT" "$BSDINSTALL_CHROOT"
 	fi
 
 	#
@@ -1657,7 +1658,7 @@
 		                "$vdev_type" $ZFSBOOT_DISKS || continue
 
 		# To be reused by bootconfig
-		echo "$ZFSBOOT_DISKS" > /tmp/bsdinstall-zfsboot
+		echo "$ZFSBOOT_DISKS" > ${TMPDIR:-"/tmp"}/bsdinstall-zfsboot
 
 		break # to success
 		;;