First of all,
Open the network settings and set the your system wide network proxy. Network -> Network proxy -> Configure -> Apply system wide.
~ Denotes Home Folder
export http_proxy=http://USERNAME:PASSWORD@SERVER:PORT/
export https_proxy=https://USERNAME:PASSWORD@SERVER:PORT/
Acquire::http::Proxy "http://USERNAME:PASSWORD@SERVER:PORT";
Acquire::https::Proxy "https://USERNAME:PASSWORD@SERVER:PORT";
export http_proxy=http://USERNAME:PASSWORD@SERVER:PORT/
export https_proxy=https://USERNAME:PASSWORD@SERVER:PORT/
export http_proxy="http://USERNAME:PASSWORD@SERVER:PORT/"
export https_proxy="https://USERNAME:PASSWORD@SERVER:PORT/"
Example especially for NIT Silchar LAN User's, thanks to CCC :D
SERVER: 172.16.30.20 PORT: 8080
export http_proxy=http://172.16.30.20:8080/
export https_proxy=https://172.16.30.20:8080/
Acquire::http::Proxy "http://172.16.30.20:8080";
Acquire::https::Proxy "https://172.16.30.20:8080";
export http_proxy=http://172.16.30.20:8080/
export https_proxy=https://172.16.30.20:8080/
export http_proxy="http://172.16.30.20:8080/"
export https_proxy="https://172.16.30.20:8080/"
sudo dpkg -i DEB_PACKAGE sudo apt-get install -f tar -zxvf file.tar.gz
gedit ~/.bashrc
JAVA_HOME=/opt/jdk-9.0.1/bin export JAVA_HOME PATH=$PATH:$JAVA_HOME export PATH
$ lsb_release -a
$ sudo apt install update-manager-core $ sudo do-release-upgrade