Ubuntu – How to set a system wide proxy with a username and password

You can use cntlm to manage ISA proxy settings.

To get around the catch 22 of installing it, without Ubuntu Software Center being able to connect to the internet, open synaptic, choose to install cntlm and go to File->Generate package download script. Open the script in a text editor and download and install the package manually.

There is a very thorough guide to configure cntlm here.

First of all, if you are behind a Web Proxy to go to the Internet, you cannot use ping to test the connection to Internet. This is because ping is not able to use any proxy to do its work, it is using its own protocol : ICMP to send and receive packet. Web proxies works only for the TCP protocol.

So if you are able to open any web site in your web browser, then you can be sure that your connection to Internet is working, no reason to do ping to double-check that.

Now regarding your problem with the package manager, if you go to System Settings -> Network, you can there define a Web Proxy configuration and apply it system-wide. When I do so on my laptop, I'm able to use apt-get without manually configuring Proxy directives into its configuration files. To work, you have to open your terminal after having clicked the Apply system-wide button. (Setting cannot be applied to already running program, only to those starting after you apply the settings).

UPD: More about Proxies and authentication

Another source of problem, as you are in Windows environment, may be the authentication mechanisms used on your web proxy. If this proxy is configured to use NTLM, it is possible that some application cannot authentify to it. In this case, what you can do is to install a local proxy supporting NTLM like cntlm, running it on 127.0.0.1 is enough and pointing it to your real Web Proxy. Then just use this local proxy as default proxy for your Ubuntu system.