I was trying to perform upgrade from Debian 6 to 7.11 (wheezy). I've changed sources.list to:
deb http://ftp.debian.org/debian/ wheezy main contrib non-free
deb-src http://ftp.debian.org/debian/ wheezy main
deb http://security.debian.org/ wheezy/updates main contrib non-free
deb-src http://security.debian.org/ wheezy/updates main
deb http://ftp.debian.org/debian/ wheezy-updates main contrib non-free
deb-src http://ftp.debian.org/debian/ wheezy-updates main
deb http://ftp.debian.org/debian/ wheezy-backports main contrib non-free
And started by apt-get update, then apt-get upgrade and finally apt-get dist-upgrade
After all these steps I've got in file /etc/debian_version value 7.11 but I can't do nothing using apt because of following error:
root@server:~# apt-get dist-upgrade
apt-get: /usr/local/lib/libstdc++.so.6: version `GLIBCXX_3.4.15' not found (required by apt-get)
apt-get: /usr/local/lib/libstdc++.so.6: version `GLIBCXX_3.4.15' not found (required by /usr/lib/x86_64-linux-gnu/libapt-pkg.so.4.12)
root@server:~# apt-get update
apt-get: /usr/local/lib/libstdc++.so.6: version `GLIBCXX_3.4.15' not found (required by apt-get)
apt-get: /usr/local/lib/libstdc++.so.6: version `GLIBCXX_3.4.15' not found (required by /usr/lib/x86_64-linux-gnu/libapt-pkg.so.4.12)