Proxy settings for apt in Ubuntu

For proxy settings in Ubuntu
create a new file called "apt.conf"  in the folder "/etc/apt/" and 
add this line to the file 
acquire::http::proxy "http://username:password@proxysereveraddress:portnumber";


ex: http::proxy "http:://mc09mt13:******@10.0.0.21:3128";

thats it now you can install any software using 


apt-get install *****