Error when creating unaccent extension on PostgreSQL
You need to install the package postgresql-contrib-9.1 in your system first. (Adapt to your version number! Here is the currently available list of packages.) That's the case under Debian, Ubuntu & friends anyway. Using a system user with the necessary privileges:
apt-get install postgresql-contrib-9.1If your currently logged in user does not have the necessary privileges (but sudo rights):
sudo apt-get install postgresql-contrib-9.1Quoting the PostgreSQL Apt Repository:
If the version included in your version of Debian is not the one you want, you can use the PostgreSQL Apt Repository.
There are basic install instructions on the Postgres website for each available OS.
For accent-insensitive indices using unaccent consider this related question:
On CentOS:
sudo yum install postgres*contrib