How do I install/enable the uuid-ossp extension on Postgres 9.3? I’m using Postgres 9.3 on Ubuntu Linux 14.04.  How do I install/enable the uuid-ossp extension?  I first verified the contrib package was installed …

root@prodbox:/home/rails/myproject# apt-get install postgresql-contrib
Reading package lists... Done
Building dependency tree       
Reading state information... Done
postgresql-contrib is already the newest version.


and then I logged in and tried to create the extension …

root@prodbox:/home/rails/myproject# su - postgres
postgres@prodbox:~$ psql
psql (9.6.0, server 9.3.11)
Type "help" for help.

postgres=# CREATE EXTENSION "uuid-ossp";
ERROR:  could not open extension control file "/usr/share/postgresql/9.3/extension/uuid-ossp.control": No such file or directory


I’m all out of ideas.  What am I missing?
You seem to have two versions (9.6 and 9.3) installed (because the psql version is 9.6).  Because the postgresql-contrib package automatically defaults to the currently supported PostgreSQL database contrib package (as noted if you do apt-cache show postgresql-contrib), you'll have to install the contrib package for 9.3:

apt-get install postgresql-contrib-9.3