Setting proxy for Software center and Synaptic package manger (Xubuntu)

The proxy for APT can be set in Xubuntu by following these steps:

• Open a Terminal
• Open the file /etc/apt/apt.conf in an editor by entering the command:
  $ sudo leafpad /etc/apt/apt.conf &
  Note: The file may not exist initially.
• Include the following lines in the file:
  
  Acquire::http::proxy "http://<proxy>:<port>/";
  Acquire::ftp::proxy "ftp://<proxy>:<port>/";
  Acquire::https::proxy "https://<proxy>:<port>/";
  
  Eg: Acquire::http::proxy "http://192.10.12.13:8080/";
• Save the file
• Reboot/ restart

Note:

• If you need authentication include "<username>:<password>@" before the proxyserver name.
  Eg: Acquire::http::proxy "http://<username>:<password>@<proxy>:<port>/";
  Acquire::http::proxy "name:password@http://192.10.12.13:8080/";
• The proxy for Synaptic package manager can also be set from its menu. 
• Leafpad is a text editor. You can use any text editor instead of it.
• Do not forget the ';' at the end of each line. 
• The '&' at the end of the command opens the file as a new process. If it is omitted the Terminal window will be locked until the file is closed.