admin@cs7003:~$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 14.04.1 LTS
Release:	14.04
Codename:	trusty

admin@cs7003:~$ sudo apt-get install postgresql-9.1
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package postgresql-9.1 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'postgresql-9.1' has no installation candidate