filesystem mount problem

Hi:

FreeBSD FreeBSD_13 13.0-CURRENT FreeBSD 13.0-CURRENT #102 r350187: Sat Jul 
20 19:04:30 EDT 2019 
root_at_FreeBSD_13:/usr/obj/usr/src/amd64.amd64/sys/MYKERNEL  amd64 1300036

I would appreciate some help with the following problem.

/etc/fstab:
# Device	Mountpoint	FStype	Options	Dump	Pass#
/dev/ada0p2	none		swap	sw	0	0
/dev/ada0p3	/		ufs	rw	1	1
linprocfs   /compat/linux/proc	linprocfs	rw	0	0
tmpfs    /compat/linux/dev/shm	tmpfs	rw,mode=1777	0	0


# df -h
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ada0p3    428G    245G    149G    62%    /
devfs          1.0K    1.0K      0B   100%    /dev
linprocfs      4.0K    4.0K      0B   100%    /compat/linux/proc
tmpfs           47G    4.0K     47G     0%    /compat/linux/dev/shm
tmpfs           20M    604K     19M     3%    /tmp

I don't understand why the /tmp is being mounted.  It is causing problems 
because when I try to run portupgrade it fails for lack of space.  If I 
forcibly unmount it everything breaks.

# umount -v /tmp
umount: unmount of /tmp failed: Device busy
[root_at_FreeBSD_13 ~]# umount -vf /tmp
tmpfs: unmount from /tmp
[root_at_FreeBSD_13 ~]# df -h
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ada0p3    428G    245G    149G    62%    /
devfs          1.0K    1.0K      0B   100%    /dev
linprocfs      4.0K    4.0K      0B   100%    /compat/linux/proc
tmpfs           47G    4.0K     47G     0%    /compat/linux/dev/shm
[root_at_FreeBSD_13 ~]# vinagre
Unable to init server: Could not connect to 127.0.0.1: Connection refused

(vinagre:27111): Gtk-WARNING **: 15:04:21.599: cannot open display: :0

Any help would be appreciated, thanks in advance.