Debian, rightfully so, retired the lenny distribution some time ago. Unfortunately, every now and then there might be a system sitting out there that still has it running. For security reasons it is very important that you upgrade your system to a newer distribution, sometimes it's necessary to install a package or two in order to help facilitate that goal.
If you find yourself in such an unfortunate problem, you may need the follow two pieces of information.
You definitely need to update your /etc/apt/sources.list to reflect lenny's move to archive status.
- Use your text editor (vi, vim, pico, nano, etc) to open the /etc/apt/sources.list file.
- Comment out (or delete) your existing repository entries by placing a hash (#) in front of the lines.
- Now paste the entry below into the file and save it.
deb http://archive.debian.org/debian/ lenny contrib main non-free
Now, this might work for you without other efforts but there's also a good chance that lenny may try to use IPv6 name resolution which may fail. In the event that this failure happens, the easiest method I've found to resolve (without a reboot) is to "ping" archive.debian.org and copy the IP address that is returned into your /etc/hosts file.
This will, in a manner of speaking, hard-link your archive.debian.org connection to that IP, however, it will get you access to the repository by bypassing the IPv6 problems.
Now you should be able to perform an apt-get update and retrieve packages as needed until you can upgrade.