I installed dovecot 2.0.13 with postfix in ubuntu server 11.10 , after installation I can send e-mail with the mail command and dovecot works when I test it with telnet

I then installed roundcube on it , and the installation passed all tests.

I want to authorize dovecot with system users through pam so I wrote in my dovecot.conf :

passwd pam {

 args = *

}

and in pam.d/dovecot I wrote :

auth    required        pam_unix.so nullok
account required        pam_unix.so

then when I reload dovecot and try to login it still fails.

So how can I solve this ?