Updating Ubuntu from inside the corporate network

Question

After connecting my computer to the corporate network I don't have direct Internet access. This is done now through some proxy server. I can connect to the Internet from Firefox by the following way:

Preferences - Advanced - Network - Connection - Settings - Automatic proxy configuration URL: http://some_path/some_file.pac

So, Firefox is OK. But all Install/Update functions don't work. For example, this is Synaptic Package Manager error message:

The repository may no longer be available or could not be contacted because of network problems.
Failed to fetch http://il.archive.ubuntu.com/ubuntu/dists/lucid/Release.gpg  Something wicked happened resolving 'il.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://il.archive.ubuntu.com/ubuntu/dists/lucid/main/i18n/Translation-en_US.bz2  Something wicked happened resolving 'il.archive.ubuntu.com:http' (-5 - No address associated with hostname)
...

It looks like I need to explain to my OS, how to connect to the Internet. How can I do this? Ubuntu version is 10.04.

Edit: After setting Network Proxy, as described in kingmilo's answer, I still have the same problem. For example:

alex@alex-ubuntu:~$ sudo apt-get install execstack
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  linux-headers-2.6.32-21 linux-headers-2.6.32-21-generic
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
  libelfg0
The following NEW packages will be installed:
  execstack libelfg0
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 134kB of archives.
After this operation, 410kB of additional disk space will be used.
Do you want to continue [Y/n]? y
WARNING: The following packages cannot be authenticated!
  libelfg0 execstack
Install these packages without verification [y/N]? y
Err http://il.archive.ubuntu.com/ubuntu/ lucid/main libelfg0 0.8.13-1
  Something wicked happened resolving 'il.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Err http://il.archive.ubuntu.com/ubuntu/ lucid/main execstack 0.0.20090925-1
  Something wicked happened resolving 'il.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://il.archive.ubuntu.com/ubuntu/pool/main/libe/libelf/libelfg0_0.8.13-1_i386.deb  Something wicked happened resolving 'il.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://il.archive.ubuntu.com/ubuntu/pool/main/p/prelink/execstack_0.0.20090925-1_i386.deb  Something wicked happened resolving 'il.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

Edit 2.

nslookup www.google.com
Server:     10.192.188.72
Address:    10.192.188.72#53

** server can't find www.google.com: NXDOMAIN

Answer 1

Go to System Settings | Network | Network Proxy and Apply System-Wide, that will configure Ubuntu to use the corporate proxy for Internet access across all applications.

If you would like to set the proxy explicitly for your console session, ie. the terminal window you are currently using you can use the export command:

export http_proxy="address:port"

Hope this helps.

Answer 2

Put your proxy settings into Synaptic.

Settings -> Preferences -> Network -> Manual proxy configuration.

Enter the .pac in HTTP proxy, and you will probably have to put the right port and authentication details in too.