hi friends,
few days back i installed ubuntu 12.10 on my machine and then i found that i was not able to update my operating system nor was i able to download any package from the software center.
Basically, i use a proxy settings to get connected to the internet. In my previous version, i used to update /etc/apt/apt.conf file with proxy credentials to get the system updated or to download any repository.
But in this version, i cannot see /etc/apt/apt.conf file where i can fill in the proxy credential details.
in the /etc/apt/apt.conf file i used to enter the following data that allowed me to update, upgrade
Acquire::http:

roxy "http://mtan_201412:xxxx@192.168.1.103:3128/";
Acquire::https:

roxy "https://mtan_201412:xxxxxx@192.168.1.103:3128/";
Acquire::ftp:

roxy "ftp://mtan_201412:xxxxx@192.168.1.103:3128/";
Acquire::socks:

roxy "socks://mtan_201412:xxxxxxx@192.168.1.103:3128/"
where mtan201412 used to be my username to access internet through proxy and 192.168.1.103 used to be address of the proxy server i was using and xxx used to be the password for logging
what am i supposed to do next in order to update or upgrade my system?