E: Пакет 'postgresql-9.4' не имеет никакого кандидата установки

$ sudo apt-get install postgresql-9.4
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package postgresql-9.4 is not available, but is referred to by another package.
This mean that the package is missing, has been obsoleted, or is only available from another source

E: Package 'postgresql-9.4' has no installation candidate

Я использую Ubuntu 16.04.

Как я могу зафиксировать это?