apt-get update fails to fetch files,"Temporary failure resolving …" error

overview

There are two parts to your question:

• fixing temporary resolve messages
• fixing the package management issues

Temporary resolve

It is likely that this issue is either:

• temporary due to your Internet Service Provider not correctly forwarding internet naming (DNS) to either its or external DNS servers, or
• due to a change in your network has similarly blocked this naming - for example, new router/modem, reconfiguring a switch with a new configuration.

Lets look at the possible DNS resolving issues.

First, temporarily add a known DNS server to your system.

echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf > /dev/null

Then run sudo apt-get update.

If this fixes your temporary resolving messages then either wait for 24 hours to see if your ISP fixes the issue for you (or just contact your ISP) - or you can permanently add a DNS server to your system:

echo "nameserver 8.8.8.8" | sudo tee /etc/resolvconf/resolv.conf.d/base > /dev/null

8.8.8.8 is Google's own DNS server.

source

Another example DNS server you could use is OpenDNS - for example:

echo "nameserver 208.67.222.222" | sudo tee /etc/resolvconf/resolv.conf.d/base > /dev/null

package-management issues

In addition to the temporary resolve issues - you have a few package management issues that need to be corrected - I'm assuming you have tried recently to upgrade from one Ubuntu version to the next recommended version - in your case from Natty (11.04) to Oneiric (11.10)

Open a terminal and type

sudo nano /etc/apt/sources.list

Look for lines that have your a different distribution name in the list than you were expecting - in your case - you have upgraded to oneiric but you have another release name natty

For example, look for lines that look like deb http:/archive.canonical.com/ natty backports

Add a # to the beginning of the line to comment it out - for example

#deb http:/archive.canonical.com/ natty backports

Save and re-run:

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

You should not have any more release naming errors.

 At the time of writing this, possible common release names include lucid, maverick, natty,oneiric, precise and quantal

http://askubuntu.com/questions/91543/apt-get-update-fails-to-fetch-files-temporary-failure-resolving-error