Ubuntu – install php 5.3.9 in ubuntu 12.04 via apt-get – what repository should I add

The ubuntu version of php you have installed does not necessarily have the same version number as the upstream bugfix release, even though the ubuntu release have backported the bugfix into its package.

apt-get dist-upgrade should bring you up to date with the latest security patches from the ubuntu repositories. Check out the link below for ubuntu's changelog on bugfixes in this particular package.

http://changelogs.ubuntu.com/changelogs/pool/main/p/php5/php5_5.3.10-1ubuntu3.2/changelog

if you get the reply that some version was not found, it probably wasn't in the repository.

try doing apt-cache search php5 to see what versions are available.

Otherwise, if there is no package available, you could add the http://www.dotdeb.org/ repository by doing this: sudo echo "deb http://php53.dotdeb.org stable all" >> /etc/apt/sources.list. Then another apt-get update and then you should have a php5.3 package available.