Apt-get connects to Web

How?

Apt.conf?

In every use of apt-get, the system is automatically used agent, so the installation software is not successful, in addition to my Ubuntu, outside the network can be on, with Firefox can be online.

Well, you probably have a proxy set up in the config file, like a 8000-port proxy, sudo gedit/etc/apt/apt.conf, which shows:
Acquire::http::p Roxy "Http://127.0.0.1:8000/";
Acquire::ftp::p Roxy "Ftp://127.0.0.1:8000/";
Acquire::https::p Roxy "Https://127.0.0.1:8000/";
Remove it.
How do you want to use the proxy temporarily with: sudo apt-get-o acquire::http::p roxy= "http://127.0.0.1:8000/" update
Note: It is not possible to set up an agent in this way by setting the HTTP_PROXY environment variable directly in export, which cannot be used after ubuntu10.04.

Thank you very much, but you said two ways, I have tried: already emptied/etc/apt/apt.conf, or useless; the/etc/apt/apt.conf file deleted also useless, do not know what is going on ~ ~

Are you sure that your apt-get is the result of the use of a proxy that causes the download to fail, not other reasons? Apt-get is based on the configuration file Settings agent, you have deleted, then the agent also canceled, I think there are other reasons.

Apt-get connects to Web