overlayfs mount error - Linux

On ubuntu 12.04

$ sudo mount -t overlayfs overlayfs -o \
rw,lowerdir=/home/user/moz,uppderdir=/aufsmp/mozilla /home/user/.mozilla

mount: wrong fs type, bad option, bad superblock on overlayfs,
missing codepage or helper program, or other error
(for several filesystems (e.g. nfs, cifs) you might
need a /sbin/mount.<type> helper program)
In some cases useful info is found in syslog - try
dmesg | tail or so

我想不出來有哪裡錯了...

btw,原本aufs用的好好的，可是support droped...
不太懂為什麼aufs進不了mainline kernel

iBus選字：按<Down>時，有選字（按數字的時候字會變），但看不到選字視窗

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