Run “sudo apt-get update” through Proxy In Ubuntu 14.04

                                       In some releases sudo is configured in such a way that all environment variables all cleared when running the command. To keep the value for your http_proxy and fix this, you need to edit /etc/sudoers,

Defaults env_keep = "http_proxy https_proxy ftp_proxy DISPLAY XAUTHORITY"

Note :- For modifying the /etc/sudoers, we need to set writable permission.but sometime after setting the Permission and Updating Proxy values (As mentioned above), it will shows some error like

Solve “sudo: /etc/sudoers.d is world writable”

                                      pkexec will use a different method of using root permissions, bypassing the issue.And the chmod will fix the permissions.

pkexec chmod 0440 /etc/sudoers