Fix fetching updates:
When you get “Unable to fetch some archives, maybe run apt-get update or try with –fix-missing?” error do this:
cd /etc/apt
mv sources.list sources.list.old
lsb_release -a
sudo cat sources.list.old |grep RELEASECODENAME |grep -v "#" |sed 's|us.archive.|old-releases.|g' >> sources.list
(del and retype >> in console if error occures)
https://www.tech-notes.net/issues-wit-apt-ubuntu-12-04/