yourid@yourid-VirtualBox:~$ dd if=/dev/zero of=disk1.img bs=1024 count=8192

yourid@yourid-VirtualBox:~$ dd if=/dev/zero of=disk2.img bs=1024 count=8192

yourid@yourid-VirtualBox:~$ ls -l *.img

yourid@yourid-VirtualBox:~$ mkfs disk1.img

yourid@yourid-VirtualBox:~$ mkfs -t vfat disk2.img

yourid@yourid-VirtualBox:~$ mkdir /tmp/ext
yourid@yourid-VirtualBox:~$ mkdir /tmp/fat

yourid@yourid-VirtualBox:~$ sudo mount disk1.img /tmp/ext
yourid@yourid-VirtualBox:~$ sudo mount disk2.img /tmp/fat

yourid@yourid-VirtualBox:~$ df

yourid@yourid-VirtualBox:~$ sudo mkdir /tmp/ext/jdb
yourid@yourid-VirtualBox:~$ sudo mkdir /tmp/fat/jdb

yourid@yourid-VirtualBox:~$ ls -l /tmp/ext

yourid@yourid-VirtualBox:~$ ls -lR /tmp/ext

yourid@yourid-VirtualBox:~$ ls -lR /tmp/fat

yourid@yourid-VirtualBox:~$ sudo chown yourid /tmp/ext/jdb

yourid@yourid-VirtualBox:~$ sudo chown yourid /tmp/fat/jdb
chown: changing ownership of '/tmp/fat/jdb': Operation not permitted

yourid@yourid-VirtualBox:~$ sudo umount /tmp/fat
yourid@yourid-VirtualBox:~$ sudo mount -o uid=yourid disk2.img /tmp/fat

yourid@yourid-VirtualBox:~$ ls -lR /tmp/fat
/tmp/fat:
total 4
drwxr-xr-x 2 yourid root 4096 Sep 30 13:11 jdb

/tmp/fat/jdb:
total 0

yourid@yourid-VirtualBox:~$ cp /etc/passwd /etc/group /tmp/ext/jdb/
yourid@yourid-VirtualBox:~$ cp /etc/passwd /etc/group /tmp/fat/jdb/

yourid@yourid-VirtualBox:~$ df

yourid@yourid-VirtualBox:~$ df /tmp/ext /tmp/fat
Filesystem     1K-blocks  Used Available Use% Mounted on
/dev/loop16         7931    50      7472   1% /tmp/ext
/dev/loop17         8164    12      8152   1% /tmp/fat

yourid@yourid-VirtualBox:~$ sudo umount /tmp/ext
yourid@yourid-VirtualBox:~$ sudo umount /tmp/fat

yourid@yourid-VirtualBox:~$ sftp yourid@montreat.cs.unca.edu
sftp> lls
sftp> put disk?.img