I have recently installed Ubuntu 14.0.1 version on my machine. I use a proxy server to access internet and for this I have to provide the necessary IP address of the proxy server, port number and my authentication credentials. Here is how my /etc/apt/apt.conf looks likeAcquire::http::proxy http://username:password@192.168.1.107:3128/;Acquire::https::proxy https://username:password@192.168.1.107:3128/;Acquire::ftp::proxy ftp://username:password@192.168.1.107:3128/;Acquire::socks::proxy socks://username:password@192.168.1.107:3128/Here mtan_201412 is username and zq8ap612g5 is the password.After installing the Ubuntu OS, I made the above apt.conf file and then ran the commandsudo apt-get updateI got a similar output asenter code hereIgn http://archive.ubuntu.com trusty-backports/multiverse Translation-en_INIgn http://archive.ubuntu.com trusty-backports/multiverse Translation-enIgn http://archive.ubuntu.com trusty-backports/restricted Translation-en_INIgn http://archive.ubuntu.com trusty-backports/restricted Translation-enIgn http://archive.ubuntu.com trusty-backports/universe Translation-en_INIgn http://archive.ubuntu.com trusty-backports/universe Translation-enErr http://archive.ubuntu.com trusty/universe Sources  407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty/mainSources 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty/restricted Sources 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty/multiverse Sources 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty/main i386 Packages 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty/restricted i386Packages 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty/universe i386 Packages 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty/multiverse i386 Packages 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty-security/universe Sources 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty-security/main Sources 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty-security/restricted Sources 407  Proxy Authentication RequiredErr http://archive.ubuntu.com trusty-security/multiverse SourcesAs is evident, there are some targets that get a hit while for others, The proxy authentication failed message is displayed. Then the above apt.conf file automatically gets changed to Acquire::http::proxy http://192.168.1.107:3128/;Acquire::https::proxy https://192.168.1.107:3128/;Acquire::ftp::proxy ftp://192.168.1.107:3128/;Acquire::socks::proxy socks://192.168.1.107:3128/;This thing happens repeatedly. Its really frustrating to keep on editing the the apt.conf file to include credentials. Why is it happening?Prior to this, I was using the same OS. I used to enter network proxy settings in the System Settings->Network->Network Proxy tab and put the credentials in the apt.conf file and everything (update, upgrade and software install through software-center) used to take place without any problem. Now I am able to upgrade the system usingsudo apt-get upgradeBut I am not able to use Software Updater GUI edition and software center to install any software.Why am I facing this problem now?I am also including the software settings
proxy authentication failed but for selected packages only
apt;authentication;http proxy