ls /overlay/
etc    upper  work

ls /overlay/upper/
etc   home  lib   root  sbin  usr   www   www1

df -h
Filesystem                Size      Used Available Use% Mounted on
rootfs                    7.2G     51.9M      7.2G   1% /
/dev/root                 2.5M      2.5M         0 100% /rom
tmpfs                    13.9M    608.0K     13.3M   4% /tmp
/dev/sda1                 7.2G     51.9M      7.2G   1% /overlay
overlayfs:/overlay        7.2G     51.9M      7.2G   1% /
tmpfs                   512.0K         0    512.0K   0% /dev
tmpfs                    13.9M    608.0K     13.3M   4% /www1/last.txt

/dev/root on /rom type squashfs (ro,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,noatime)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,noatime)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noatime)
/dev/sda1 on /overlay type ext4 (rw,relatime,data=ordered)
overlayfs:/overlay on / type overlay (rw,noatime,lowerdir=/,upperdir=/overlay/upper,workdir=/overlay/work)
tmpfs on /dev type tmpfs (rw,nosuid,relatime,size=512k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,mode=600)
debugfs on /sys/kernel/debug type debugfs (rw,noatime)
tmpfs on /www1/last.txt type tmpfs (rw,nosuid,nodev,noatime)