How to update Debian 6 Squeeze

After a Debian version has reached EOL (end of life), its repositories go to the Debian archive. Therefore we can use this archive to get packags for our distribution. The syntax for our /etc/apt/sources.list is as follows:

deb http://archive.debian.org/debian/ <version> main non-free contrib
deb-src http://archive.debian.org/debian/ <version> main non-free contrib

deb http://archive.debian.org/debian-security/ <version>/updates main non-free contrib
deb-src http://archive.debian.org/debian-security/ <version>/updates main non-free contrib

So for Debian Etch, you’d comment out all other repositories in /etc/apt/sources.list and add the following lines:

vi /etc/apt/sources.list

deb http://archive.debian.org/debian/ etch main non-free contrib
deb-src http://archive.debian.org/debian/ etch main non-free contrib

deb http://archive.debian.org/debian-security/ etch/updates main non-free contrib
deb-src http://archive.debian.org/debian-security/ etch/updates main non-free contrib

Run

apt-get update

afterwards to update the packages database.

If you get an error like

W: There is no public key available for the following key IDs: 9AA38DCD55BE302B
W: GPG error: http://archive.debian.org etch/updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9AA38DCD55BE302B
W: You may want to run apt-get update to correct these problems

just install the debian-archive-keyring package…

apt-get install debian-archive-keyring

… and run

apt-get update

again.