Ubuntu (family) OS proxy setting

System Wide:

Step 1:

    Open "/etc/environment" file in edit mode
    or
    Run the following command in terminal
    sudo gedit /etc/environment

Step 2:

    Add the following lines in that file and then Save & Close

        http_proxy="http://username:password@proxyserver:port/"
        https_proxy="http://username:password@proxyserver:port/"
        ftp_proxy="http://username:password@proxyserver:port/"
        all_proxy="http://username:password@proxyserver:port/"

    If proxy server does not require any username and password, then the format will be:
        http_proxy="http://proxyserver:port/"
        https_proxy="http://proxyserver:port/"
        ftp_proxy="http://proxyserver:port/"
       all_proxy="http://proxyserver:port/"

User Specific:

Step 1:

    Open "~/.profile" file in edit mode
    or
    Run the following command in terminal
    gedit ~/.profile

Step 2:

    Add the following lines in that file and then Save & Close

        export http_proxy="http://username:password@proxyserver:port/"
        export https_proxy="http://username:password@proxyserver:port/"
        export ftp_proxy="http://username:password@proxyserver:port/"
        export all_proxy="http://username:password@proxyserver:port/"

    If proxy server does not require any username and password, then the format will be:
        export http_proxy="http://proxyserver:port/"
        export https_proxy="http://proxyserver:port/"
        export ftp_proxy="http://proxyserver:port/"
        export all_proxy="http://proxyserver:port/"