How to install software or upgrade softwares in unsupported Ubuntu releases

If you have old computers, then it is good option to install light Linux distribution like Lubuntu or Xubuntu. If you have installed the old Ubuntu version which is  Whenever you try to install softwares, you will get an error "Couldn't find package firefox"

$ sudo apt-get install firefox
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package firefox

This is because repositories for older releases are not supported. The repositories are moved to an archive server. There are repositories available at

To change repositories url in server, run the below command in Terminal.

sudo sed -i -re 's/([a-z]{2}\.)?|' /etc/apt/sources.list

This will change and to in /etc/apt/sources.list file.

then update repositories with command:

sudo apt-get update && sudo apt-get dist-upgrade

Once you have performed the above steps to switch to the old-releases mirrors, update the Update Manager and then do do-release-upgrade:

sudo apt-get update
sudo apt-get install ubuntu-release-upgrader-core
sudo do-release-upgrade

Though it is advised not to use unsupported versions as there is no security updates but you can still use them and enjoy old nostalgic feeling.