我运行Ubuntu12.04。/ubuntu/dists/precise/main/source/Sources 404 Not Found
W: Failed to fetch http://ftp.availo.se/ubuntuftp.availo.se/ubuntu/dists/precise-backports/main/binary
of the distribution.
deb http://ubuntu.mirrors.ovh.net/ftp.ubuntu.com/ubuntu/ trusty main restricteddeb-src http://ubuntu.mirrors.ovh.net/ftp.ubuntu.com/ubuntu/ trusty main restr
://ftp.iinet.net.au/pub/ubuntu/dists/raring-backports/restricted/binary-amd64/Packages: 404 Not FoundW: Failed to fetch http://ftp.iinet.net.au/pub/ubuntu/dists/raring-backports/unive