13.04 has reached EOL there for the repositories have been removed so there will be no more updates for 13.04 not even security so it is vulnerable to attacks. There is an archive here that you can use to install software but it will be old software outdated and there will be no improvements and no new security update.

Lubuntu is a flavor of Ubuntu based on the Lightweight X11 Desktop Environment (LXDE), as its default GUI. The goal is to provide a very lightweight distribution, with all the advantages of the Ubuntu world (repositories, support, etc.). How to install apt-add-repository on Ubuntu 13.04 – Random Jun 02, 2013 Ubuntu Sources List Generator - Simply Linux Sources List Generator for Ubuntu, Xubuntu, Kubuntu, Edubuntu, Ubuntu Server and other Ubuntu-based distros. It features the official Canonical one repositories as well as other 3rd party repos.

Install Oracle Java (JDK) 6 / 7 / 8 in Ubuntu 13.04

So, if you want to ensure that you have the latest software installed on Ubuntu, you might want give GetDeb and PlayDeb repository a try! Add GetDeb repository on Ubuntu 13.04 Raring Ringtail Adding GetDeb repository is a piece of cake. Please execute the following command: Mate 1.6 Desktop Released, Install it in Ubuntu 13.04/12 Install Mate Desktop 1.6 in Ubuntu 13.04 Raring/Ubuntu 12.10 Quantal/Ubuntu 12.04 Precise/11.10/Linux Mint 14/13/12 The GNOME 2 Fork 'Mate' is a desktop environment. If you wish to use this desktop environment on Ubuntu to replace your current desktop interface.

It seems like you're using Ubuntu 13.04 (Raring Ringtail) and it is no longer supported since Jan 27, 2014. In case you don't want to update yet, you could also replace both archive.ubuntu.com and security.ubuntu.com with old-releases.ubuntu.com in your sources.list file (may be simply use the script I wrote that does the same thing automatically)

Aug 25, 2013 Where can I get the repositories for old Ubuntu versions Where can I get the old repositories for Ubuntu versions? In my case, it's 9.04 Jaunty? I found all the official repositories and their mirrors have been removed. I am wondering where I can get the repository list for this version? How To Add Apt Repository In Ubuntu | Linuxize Aug 26, 2019 Repositories/Ubuntu - Community Help Wiki Sep 06, 2017