root@stux ~ # cat /etc/apt/sources.list
## main & restricted repositories
deb http://archive.ubuntu.com/ubuntu/ lucid main restricted
deb-src http://archive.ubuntu.com/ubuntu/ lucid main restricted

deb http://security.ubuntu.com/ubuntu lucid-updates main restricted
deb-src http://security.ubuntu.com/ubuntu lucid-updates main restricted

deb http://security.ubuntu.com/ubuntu lucid-security main restricted
deb-src http://security.ubuntu.com/ubuntu lucid-security main restricted

deb http://archive.canonical.com/ubuntu lucid partner
deb http://archive.canonical.com/ubuntu lucid partner

## universe repositories - uncomment to enable
deb http://archive.ubuntu.com/ubuntu/ lucid universe
deb-src http://archive.ubuntu.com/ubuntu/ lucid universe

deb http://archive.ubuntu.com/ubuntu/ lucid-updates universe
deb-src http://archive.ubuntu.com/ubuntu/ lucid-updates universe

deb http://security.ubuntu.com/ubuntu lucid-security universe
deb-src http://security.ubuntu.com/ubuntu lucid-security universe
root@stux ~ # lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 10.04.4 LTS
Release:	10.04
Codename:	lucid
root@stux ~ # uname -a
Linux stux 4.1.5 #7 SMP Mon Aug 24 13:46:31 EDT 2015 x86_64 GNU/Linux
root@stux ~ # do-release-upgrade
Checking for a new ubuntu release
No new release found
root@stux ~ # do-release-upgrade -d
Checking for a new ubuntu release
No new release found
root@stux ~ #