finally i get a working config:
:UBUNTU
See [url]http://manpages.ubuntu.com/manpages/precise/man7/casper.7.html[/url] for casper cmdline details
kernel [url]http://192.168.0.3/fog/iso/ubuntu/casper/vmlinuz[/url]
initrd [url]http://192.168.0.3/fog/iso/ubuntu/casper/initrd.lz[/url]
imgargs vmlinuz root=/dev/nfs boot=casper netboot=nfs nfsroot=192.168.0.3:/var/www/fog/iso/ubuntu/ locale=en_US.UTF-8 keyboard-configuration/layoutcode=no mirror/country=NO
boot || goto failed
goto start
$ cat /etc/exports
/images *(ro,sync,no_wdelay,insecure_locks,no_root_squash,insecure)
/images/dev *(rw,sync,no_wdelay,no_root_squash,insecure)
/var/www/fog/iso/ubuntu/ *(ro,sync,no_wdelay,insecure_locks,no_root_squash,insecure)
administrator@fog:/var/www/fog/iso/ubuntu$ ls -la
totale 32
dr-xr-xr-x 5 root root 4096 dic 5 12:48 .
drwxr-xr-x 3 root root 4096 dic 5 12:47 …
dr-xr-xr-x 3 root root 4096 dic 9 08:37 casper
dr-xr-xr-x 2 root root 4096 ago 9 22:19 .disk
dr-xr-xr-x 2 root root 4096 ago 9 22:19 isolinux
-r-xr-xr-x 1 root root 8351 ago 9 22:20 SHA256SUMS
administrator@fog:/var/www/fog/iso/ubuntu$