If upstart (http://en.wikipedia.org/wiki/Upstart)
is the default init (PID 1) save next 

--------------------------------
# ngetty
start on runlevel [2345]
stop on shutdown
respawn
exec /sbin/ngetty 1 2 3 4 5 6
--------------------------------

in /etc/init/ngetty.tmp and then type:
mv /etc/init/ngetty.tmp /etc/init/ngetty.conf

If you have running tty stop them before above "mv" with:
stop tty1
stop tty2
...

See also:
http://upstart.ubuntu.com/getting-started.html

If someone uses ngetty with upstart and has more 
experience let me know.